Eriogonum spergulinum, the Spurry Buckwheat

Wandering around sandy highlands of the southwest United States, you may encounter a sparse, wiry weed growing between five and forty centimetres in height. This is the spurry buckwheat Eriogonum spergulinum.

Spurry buckwheat Eriogonum spergulinum, copyright Dcrjsr.

Members of the buckwheat family Polygonaceae are found worldwide but tend to be easily overlooked as low, scrubby weeds. In North America, one of the most diverse genera is Eriogonum, known from about 250 species though many are difficult to readily distinguish (Hickman 1993). Eriogonum spergulinum is one of the more recognisable species in the genus. As mentioned above, it grows in sandy soils, particularly those dominated by worn-down granite, and is found at altitudes between 1200 and 3500 metres. It is an annual herb with basal leaves of a linear shape, less than two millimetres wide but up to thirty millimetres long. The greater part of the plant's height is made up by the slender, cyme-like inflorescence bearing unribbed, four-toothed involucres on slender stalks. The flowers are up to three millimetres in diameter with a white perianth marked by darker stripes. Overall, E. spergulinum in flower resembles a drifting cloud of small white stars.

Close-up on Eriogonum spergulinum flowers, copyright Tom Hilton.

Three varieties of Eriogonum spergulinum have been recognised though they are not always distinct and tend to intergrade with each other. In most parts of the species' range, plants belong to the variety E. spergulinum var. reddingianum. This variety is characterised by erect inflorescences with glandular axes and flowers about two millimetres in diameter. The other two varieties are both restricted to the Sierra Nevada mountains of California. Eriogonum spergulinum var spergulinum resembles var. reddingianum but produces larger flowers, about three millimetres in diameter. Eriogonum spergulinum var. pratense is more distinctive. Inflorescences are prostrate to ascending, only about two to five millimetres in height, and lack glands on the axes. Flowers are only 1.5 millimetres across. Pratense is also a higher-altitude variety, found at heights above 2500 metres. The Sierra Nevada varieties are both uncommon; if any variety is likely to be found, it is the widespread reddingianum.

REFERENCE

Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

Succulent Orchids

With over 1200 known species found in Asia and Australasia, Dendrobium is one of the largest currently recognised genera of orchids. As with other examples of such 'super-genera', the question of how to best handle such a monster has been fiercely debated. In 2003, Australian botanist M. Clements proposed dividing Dendrobium between numerous segregate genera, noting (among other reasons) that the genus as previously recognised was not monophyletic. However, Clements' system does not seem to have garnered widespread usage with other orchid systematists preferring to retain a broad concept of Dendrobium (excluding some of the more egregious outliers) that largely corresponds with its established usage (e.g. Schuiteman 2011). Nevertheless, many of the subdivisions promoted by Clements remain recognised as well delimited groups. One such cluster is the assemblage of species recognised as Dendrobium section Aporum.

Growth habit of Dendrobium sect. Aporum, copyright Tony Rodd.

Species of section Aporum are epiphytes found in lowland forests of south-east Asia, extending eastwards to New Guinea and the Solomon Islands. Members of this section have thin stems that are erect at first but tend to become pendulous as they lengthen. Leaves are fleshy and equitant: that is, they are folded longitudinally with what would otherwise be the two sides of the dorsal surface fused, except at the base where they overlap with opposing leaves. The stem may be more or less completely concealed by the leaf bases. Tips of the leaves end in a point. Flowers are borne singly or in clusters, arising laterally on the stem between leaf nodes or at the tip of the stem alongside a terminal scale. The flowers may be subtended by persistent chaffy bracts. They are generally small and fleshy and tend to be short-lived, wilting after just a few days.

Flowers of Dendrobium anceps, copyright Aqiao HQ.

The functional significance of the Aporum section's distinctive leaves remains uncertain. As noted by Carlsward et al. (1997), the fleshy leaves might be taken as an adaptation to water retention. However, though access to water is a consistent concern for epiphytes, the humid rainforests in which Aporum species are found hardly seem the driest of places. Conversely, the effective even distribution of stomata on both sides of leaf resulting from their equitant condition may make it easier for excess water to be released from the plant.

Dendrobium distichum, photographed by Ronny Boos.

Orchids in general are, of course, most often considered by people as ornamental plants. My impression is that the various Aporum species tend not to be among the most widely grown of species though their unusual growth habit might attract interest. This may be due to them not being the easiest of orchids to maintain; they appear to require high humidity and warm temperatures to thrive with a cooler, drier period in the non-growing season. Among the more popular species are Dendrobium anceps and D. keithii, both of which produce small greenish flowers. Those of D. anceps have been described as having a distinct "apple pie" fragrance. Of course, if you happen to be wandering through the jungles of south-east Asia, you might well discover these plants growing of their own accord.

REFERENCES

Carlsward, B. S., W. L. Stern, W. S. Judd & T. W. Lucansky. 1997. Comparative leaf anatomy and systematics in Dendrobium, sections Aporum and Rhizobium (Orchidaceae). International Journal of Plant Sciences 158 (3): 332–342.

Clements, M. A. 2003. Molecular phylogenetic systematics in the Dendrobiinae (Orchidaceae), with emphasis on Dendrobium section Pedilonum. Telopea 10 (1): 247–298.

Schuiteman, A. 2011. Dendrobium (Orchidaceae): to split or not to split? Gardens' Bulletin Singapore 63 (1–2): 245–257.

Leandra

I'm sure I've noted before that there are a number of plant families that form significant components of the world's flora but tend to glide under the radar of popular representation owing to their largely tropical distributions. One of the prime examples is the Melastomataceae, an assemblage of over 5000 known species that represents one of the ten largest recognised plant families. Melastomes often stand out from other tropical plants by their distinctive leaves, which are opposite with acrodromous venation (several strong longitudinal veins arch outwards from the base to converge near the tip) and flowers that often bear large, colourful anthers (New York Botanical Garden). They are most diverse in the Neotropics with one of the significant genera found in this region being Leandra.

Leandra subseriata, copyright James Gaither.

As currently recognised, Leandra includes over two hundred species with the highest diversity centred in southeastern Brazil. Leandra forms part of the tribe Miconieae, distinguished by flowers with more or less inferior ovaries and fleshy berry fruits. Genera within the Miconieae have historically been difficult to define; as early as 1891, the Belgian botanist Alfred Cogniaux declared that they were essentially arbitrary. Leandra was supposed to be defined by its acute petals and terminal inflorescences but it has not always been clear whether a given species can be said to possess these features or not. It should therefore come as no surprise that the genus Leandra proved to be polyphyletic with the advent of molecular analysis (Martin et al. 2008). Nevertheless, a large clade centered on southern Brazil has continued to be referred to as Leandra sensu stricto.

There appear to be few if any direct observations of pollination in Leandra but flower morphology and comparison with related genera suggests that they are buzz-pollinated with pollinators taking pollen as a reward (Reginato & Michelangeli 2016b; buzz-pollination referring to pollination by bees where the bee's buzzing induces the flower to release pollen). Apomixis, with seeds being produced directly from ovule tissue without pollination, is not uncommon and may even be the majority condition (Reginato & Michelangeli 2016a). Seeds are dispersed by birds feeding on the berries. Many Leandra species appear very localised in distribution and they are particularly diverse in a number of high altitude areas. Species vary in their preferred habitat from disturbed to undisturbed; those species found in undisturbed locations are rare components of the understory, but those found in disturbed habitats may be among the most abundant shrubs in the area.

REFERENCES

Martin, C. V., D. P. Little, R. Goldenberg & F. A. Michelangeli. 2008. A phylogenetic evaluation of Leandra (Miconieae, Melastomataceae): a polyphyletic genus where the seeds tell the story, not the petals. Cladistics 24: 315–327.

Reginato, M., & F. A. Michelangeli. 2016. Diversity and constraints in the floral morphological evolution of Leandra s.str. (Melastomataceae). Annals of Botany 118: 445–458.

Reginato, M., & F. A. Michelangeli. 2016. Untangling the phylogeny of Leandra s.str. (Melastomataceae, Miconieae). Molecular Phylogenetics and Evolution 96: 17–32.

Lilies of Blood

The flora of southern Africa is renowned for being remarkably diverse and, in many cases, remarkably eye-catching. The region is home to more than its fair share of ornamental plants, many of which have become popular garden subjects. Among the remarkable members of the southern African flora are the blood lilies of the genus Haemanthus.

Haemanthus coccineus, copyright Peter Coxhead.

Haemanthus is a genus of 22 known species found in the very southern part of the continent, in the countries of South Africa and Namibia (species from further north that have historically been included in Haemanthus are now treated as a separate genus Scadoxus). It is a member of the belladonna family Amaryllidaceae and, like many other members of that family, grows as a herb from a fleshy bulb that is partially or entirely concealed underground. The plant above ground may be annual or persistent, depending on species. Each individual Haemanthus plant produces very few leaves at a time: two is the most common number (Van Jaarsveld 2020). The leaves are more or less fleshy, often hairy, and may be directed upwards or spread outwards.

In those species that shed their leaves, flower stalks are produced before the next season's leaves appear, in a similar matter to the related naked ladies Amaryllis belladonna. Flowers are produced in dense umbels, subtended by bracts that are often brightly coloured, so at a glance the inflorescence of some species might be taken for a single large flower up to ten centimetres in diameter. Depending on the species, the supporting stalk may vary from over a foot in height to only a few centimetres. The first species to be described bear flowers of a bright red colour, explaining both the genus and vernacular names, but flowers may also be pale pink or white. Species that lack the red colour may be referred to as 'paintbrush lilies' rather than 'blood lilies'. Fruits are soft fleshy berries.

Haemanthus albiflos, copyright Krzysztof Ziarnek, Kenraiz.

Phylogenetic analyses of the genus have identified two major clades, a mostly eastern clade found in regions with summer rainfall and a mostly western clade associated with winter rainfall. A notable outlier is the eastern summer-rainfall species H. montanus which is the sister taxon to the winter rainfall clade. Members of the summer-rainfall clade have white or pale pink flowers; members of the winter-rainfall clade have pale pink to dark red flowers. Members of both clades have been grown as pot plants for their unusual appearance though the scent of the flowers is not regarded as pleasant. Perhaps the most widely grown species is H. albiflos, a species native to both the western and eastern parts of South Africa that bears flowers in umbels up to seven centimetres wide. This species is evergreen, carrying its leaves year-round.

REFERENCE

Van Jaarsveld, E. 2020. Haemanthus. In: Eggli, U., & R. Nyffeler (eds) Illustrated Handbook of Succulent Plants: Monocotyledons 2^nd ed. pp. 441–443. Springer.

The Cordia Clade

The tropics are home to a wide diversity of plant species, many of them belonging to groups less familiar in cooler regions of the world. Prominent among these are members of the family Cordiaceae, a group of about 350 known species of mostly trees and shrubs. The Cordiaceae (alternatively treated as the subfamily Cordioideae of the family Boraginaceae) are a well distinguished clade both molecularly and morphologically. Most members of the clade have flowers with the stigma divided between four lobes, fruits with an undivided endocarp, and plicate cotyledons (Miller & Gottschling 2007).

Beach cordia Cordia subcordata, copyright Tauʻolunga.

Historically, most members of the clade have been assigned to a single genus, Cordia. This arrangement was revised by Miller & Gottschling (2007) who recognised the separate genus Varronia for about 100 species of multi-stemmed shrubs native to the New World. The remaining 250 or so species, most of them single-trunked trees, remained in the pantropical Cordia. The two genera also generally differ in their leaves (most Varronia have leaves with serrate margins whereas Cordia have entire margins) and inflorescences (most Cordia have broad cymose inflorescences whereas Varronia have smaller, more compact inflorescences). Few species of Cordiaceae are not assigned to either Cordia or Varronia. Three previously recognised small genera, Auxemma, Patagonula and Saccellium, are now synonymised with Cordia. The small African genus Hoplestigma and the prostrate annual herb Coldenia procumbens are placed in Cordiaceae primarily on the basis of molecular data (Miller & Gottschling 2007; Weigend et al. 2014).

Black sage Varronia curassavica, copyright Mauricio Mercadante.

A number of Cordia species are grown for their wood, with South American species providing timbers known as bocote, freijo (C. alliodora), and ziricote (C. dodecandra). These are only moderately strong woods but strikingly patterned and are more often used for aesthetic rather than structural purposes (such as cabinet veneers and musical instruments). Cordia alliodora has become an invasive in regions where it has been planted outside its native range such as Africa and Vanuatu. Various species are also grown for their edible fruits, such as the Assyrian plum C. myxa and the fragrant manjack C. dichotoma. These fruits are decidedly gooey when ripe and are often given names reflecting this fact such as glue berries, clammy cherries or, here in Australia, snotty gobbles (though this name is more widely used for fruits of the unrelated genus Persoonia). Pulp from unripe fruits of C. myxa can supposedly also be used as a type of glue. Your office reports may not be informative but they will at least be tasty!

REFERENCES

Miller, J. S., & M. Gottschling. 2007. Generic classification in the Cordiaceae (Boraginales): resurrection of the genus Varronia P. Br. Taxon 56 (1): 163–169.

Weigend, M., F. Luebert, M. Gottschling, T. L. P. Couvreur, H. H. Hilger & J. S. Miller. 2014. From capsules to nutlets—phylogenetic relationships in the Boraginales. Cladistics 30: 508–518.

Woolly Orchids

The orchids of the Orchidaceae are widely recognised as one of the most diverse families of plants in the modern world, both in number of species and morphologically. They are readily distinguished from other flowering plants by a unique combination of features including the fusion of the male and female organs of the flower into a central column. Rather than being released as individual grains, pollen is aggregated into compact masses called pollinia that are attached to pollinators as whole units. Most orchid species also have the lower of the flower's three petals enlarged and differentiated into a distinctive lip that may present a bewildering array of shapes and colours. Because of their striking and colourful appearance, many orchids have long attracted attention from humans and many are popular ornamentals. But there are also some major groups of orchids that have been more neglected and one such group is members of the subtribe Eriinae.

Dendrolirium tomentosum, copyright Orchi.

The Eriinae comprise about a thousand known species of orchid found mostly in the tropics of Asia and the west Pacific, with a handful of species described from Africa. Most are epiphytes and lithophytes (growing on rocks); a smaller number are terrestrial. Because the flowers of eriines tend to be fairly small and simple, they have attracted less notice than other members of the family, but in some parts of their range they are among the most abundant epiphytic orchids (Ng et al. 2018). Within the Orchidaceae, eriines are a subgroup of the subfamily Epidendroideae, characterised by compact, laterally compressed pollinia, and the tribe Podochileae, with duplicate leaves, a short and massive column, and often spherical silica cells in the stems (Szlachetko 1995). The features distinguishing Eriinae from other subtribes of Podochileae are more vague and there are reasons to believe the Eriinae ultimately represent the paraphyletic residue of the tribe once the more specialised subgroups are removed (Ng et al. 2018). One recent classification of the orchids recommended abandoning subtribes within the Podochileae altogether (Chase et al. 2015). Nevertheless, features characteristic of most eriines include a terminal or upper lateral inflorescence, eight pollinia per flower, and sticky caudicles on the pollinia composed of apical pollen grains. The lip is commonly divided into three lobes. Another common feature of the group (and the inspiration for the name of the type genus Eria, meaning 'woolly') is a covering of hairs on the flower and sometimes the inflorescence. In one genus, Trichotosia, the leaves are also hairy.

Ascidieria grandis, copyright Dick Culbert.

Historically, the majority of eriines have been included in a broad genus Eria. However, as with the subtribe as a whole, recent studies have indicated that this sense of Eria is not monophyletic and hence its species should probably be divided between several genera. Ng et al. (2018) recognised 21 genera among the eriines. The African species, previously placed in their own genus Stolzia, were united with the closely related Asian genus Porpax.

The pollination biology of eriines is, for the most part, not well known. Some have speculated that they were pollinated by beetles; one website I found showed pollinia attached to a gnat. The two species of the genus Callostylis have flowers whose appearance suggests pollination by pseudocopulation (tricking male insects into attempting to mate with them by mimicking females) but such flowers are unique within the Podochileae (Ng et al. 2018). At least some eriines have flowers producing 'pseudopollen' from broken-off hairs (Pansarin & Maciel 2017). This pseudopollen is collected and eaten by pollinators. Thus, though the most common means of attracting pollinators among orchids is via deception, at least some eriines are willing to pay their way in life.

REFERENCES

Ng, Y. P., A. Schuiteman, H. A. Pedersen, G. Petersen, S. Watthana, O. Seberg, A. M. Pridgeon, P. J. Cribb & M. W. Chase. 2018. Phylogenetics and systematics of Eria and related genera (Orchidaceae: Podochileae). Botanical Journal of the Linnean Society 186: 179–201.

Pansarin, E. R., & A. A. Maciel. 2017. Evolution of pollination systems involving edible trichomes in orchids. AoB Plants 9: plx033.

Szlachetko, D. L. 1995. Systema Orchidalium. Fragmenta Floristica et Geobotanica Supplementum 3: 1–152.

Tears of a Baby

For many people, the most familiar members of the plant family Urticaceae are the stinging nettles. However, the nettles make up only one part of this cosmopolitan family and there are many representatives that do not sting. One such plant is Soleirolia soleirolii, commonly referred to by the vernacular name of baby's tears.

Baby's tears Soleirolia soleirolii growing around dwarf horsetail Equisetum scirpoides, copyright Carnat Joel.

The only species of its genus, Soleirolia soleirolii is a small creeping herb with more or less succulent stems and subcircular leaves half a centimetre or less in diameter (Harden 1990). It grows in damp habitats and may even grow submerged in water. Baby's tears form a dense flat mat with stems rooted at the nodes. The tiny white flowers reach only a millimetre in size. Wikipedia lists a number of vernacular names for this plants, such as baby's tears, angel's tears, Corsican creeper, or mind-your-own-business (I have no idea what this last name refers to).

In its native range, Soleirolia soleirolii is mostly restricted to islands of the western Mediterranean, including Corsica, Sardinia and Majorca, with a localised mainland population near Rome in Italy (Schüßler et al. 2019). A population was also recently discovered near the coast of Algeria (Hamel & Boulemtafes 2017). On the basis of molecular phylogenetic dating, Schüßler et al. (2019) suggested that its current range may be relictual, having gone extinct over most of mainland Europe as the climate changed. However, as those who glanced at the references for this post may have already guessed, Soleirolia has now become established in many parts of the world outside its native range. It has often been grown as a ground cover or houseplant. If it finds itself somewhere it likes, it may become invasive; though easily uprooted, its proclivity for vegetative reproduction means that it can easily return if not thoroughly cleared. And so we have a paradox, where what is regarded as a valuable relict in one location may be considered a vexatious weed in another.

REFERENCES

Hamel, T., & A. Boulemtafes. 2017. Découverte d'une endémique tyrrhénienne Soleirolia soleirolii (Urticaceae) en Algérie (Afrique du Nord). Flora Mediterranea 27: 185–193.

Harden, G. J. (ed.) 1990. Flora of New South Wales vol. 1. New South Wales University Press.

Schüßler, C., C. Bräuchler, J. A. Reyes-Betancort, M. A. Koch & M. Thiv. 2019. Island biogeography of the Macaronesian Gesnouinia and Mediterranean Soleirolia (Parietarieae, Urticaceae) with implications for the evolution of insular woodiness. Taxon 68 (3): 537–556.

The New Centaury

In an earlier post, I described the South American flowering herbs known as the Coutoubeinae. In this post, I'm going to take a step back and look at a clade of which the coutoubeines form a part, the Chironieae.

Seaside centaury Centaurium littorale, copyright Anne Burgess.

The Chironieae are one of the major tribes of the flowering plant family Gentianaceae, including about 160 known species. Representatives are found in most parts of the world, though as part of the native flora in Australasia they do not extend past the north of Australia (some exotic species have been introduced further south). The Chironieae seem to primarily be supported as a clade on the basis of molecular data (Struwe et al. 2002). All members are herbs, from annuals to short-lived perennials. Most have an erect growing habit; members of the Caribbean genus Bisgoeppertia are annual climbers and some species of the Mexican genus Geniostemon are creeping perennials. There may or may not be a basal rosette of leaves, and a number of genera have winged stems. Flowers are solitary or borne in cymose or racemose inflorescences. These flowers are most commonly salver-shaped (that is, shaped like a flat dish) or tubular, and usually have four or five petals (some species may have up to twelve). The calyx is usually comprised of fused sepals and is unwinged and tubular. The fruit is usually a septicidal capsule (splitting along the septa between carpels), more rarely a berry.

Yellow centaury Cicendia filiformis, copyright Hajotthu.

Members of the Chironieae are divided between three subtribes that are mostly distinct both morphologically and biogeographically. As described in the previous post, the Neotropical Coutoubeinae are characterised by releasing their pollen in tetrads whereas the other subtribes shed individual pollen grains. The Canscorinae are mostly found in the Old World tropics and have white or cream-coloured flowers (less commonly yellow, pink or purple) with the calyx tube longer than the calyx lobes. The Chironiinae mostly includes found in northern temperate regions, as well as the southern African genera Chironia and probably the South American Zygostigma. Their flowers come in a range of colours—pink, yellow, purple or blue, but less commonly white or cream-coloured—and may have calyx lobes longer than the tube. Many chironiine flowers also have anthers that become spirally twisted after releasing pollen whereas those of Canscorinae are always straight. Molecular data usually support the monophyly of the three subtribes and the majority view seems to be that the temperate Chironiinae represent the sister group of a tropical clade of Canscorinae and Coutoubeinae.

Cultivated Eustoma, copyright Rameshng.

Perhaps the best known members of the Chironieae are the centauries of the genus Centaurium. Historically, about fifty species across the Holarctic have been included in this genus. However, phylogenetic studies have demonstrated that this broad sense of the genus is polyphyletic and thus it has been cut down to a group of about twenty species found in Europe and western Asia. The name 'centaury' refers to the use of common centaury Centaurium erythraea as a medicinal herb, after the legendary centaur healer Chiron. Other Old World species are now placed in the genus Schenkia whereas North American species form the genera Gyrandra and Zeltnera. The yellow centauries of Cicendia are small, filiform annuals native to Europe and the Americas that have been introduced to Australia. The rose gentians Sabatia of North America bear pinkish-purple flowers, often in lax cymes. There are also the prairie gentians of the genus Eustoma. Native to southern North America, these plants bear large, showy flowers that have become popular in cultivation. Commercially, they are labelled as lisianthus. This is not to confused with Lisianthius, a distinct genus of Gentianaceae, or Lisyanthus, a name that has been used in the past for members of yet another gentianaceous genus. Both of these belong to completely different tribes in the family, and may be subjects for another day.

REFERENCE

Struwe, L., J. W. Kadereit, J. Klackenberg, S. Nilsson, M. Thiv, K. B. von Hagen & V. A. Albert. 2002. Systematics, character evolution, and biogeography of Gentianaceae, including a new tribal and subtribal classification. In: Struwe, L., & V. A. Albert (eds) Gentianaceae: Systematics and Natural History pp. 21–309. Cambridge University Press: Cambridge.

The Spread of Carrots

Carrots are one of the staple vegetables in this part of the world as well as in a great many others. Indeed, Wikipedia informs us that about forty million tonnes of carrots and turnips were produced worldwide in 2018, and I would have to think that carrots accounted for the greater part of that number. Wild carrots are also a widespread weed that can commonly be seen growing in disturbed, open habitats such as roadside verges. This post is about the group of plants that carrots typify, the subtribe Daucinae.

Wild carrot Daucus carota in flower, copyright Cwmhiraeth.

Daucinae is a subgroup of the plant family Apiaceae, historically known as the Umbelliferae. The latter name refers to the characteristic production of flowers in dense, flat-topped inflorescences known as umbels. Anyone who is familiar with the appearance of carrot flower-heads is familiar with the form of an umbel; the wild form of carrot is often known as "Queen Anne's lace" in reference to said appearance. The fruit of Apiaceae species is a schizocarp, a dry fruit that splits at maturity into segments (called mericarps), each containing a single seed, that are dispersed independently. In Daucinae and related group of umbellifers, the mericarps carry longitudinal ribs, both primary ribs containing a vascular bundle and secondary ribs without. The secondary ribs of Daucinae are often modified to form broad wings or curved spines that function in the mericarp's dispersal.

Broad-leafed sermountain Laserpitium latifolium seedheads, showing wings, copyright Krzysztof Ziarnek, Kenraiz.

Historically, these differences in mericarp morphology have been used to assign the species bearing them to different tribes. However, more recent phylogenetic analyses have indicated that changes between wings and spines have occurred on multiple occasions due to changes in mode of dispersal (Wojewódzka et al. 2019). Mericarps bearing wings are generally anemochorous (dispersed by wind) whereas those bearing spines are epizoochorous (carried by animals, such as stuck to a mammal's fur). The distinction is not 100% immutable: winged seeds may sometimes get caught in fur, spined seeds may be carried slightly further by wind than smooth ones. Phylogenies indicate that anemochory was the ancestral condition for Daucinae, retained in genera such as Laserpitium and Thapsia. Epizoochorous species do not form a single clade within the Daucinae (indeed, the genus Daucus includes both anemochorous and epizoochorous species) but it is unclear to what degree epizoochory arose on multiple occasions versus reversions to anemochory from epizoochorous ancestors. Two species of Daucinae, Daucus dellacellae from the Cyrenaica region of northern Africa and Cryptotaenia elegans from the Canary Islands, have neither spines nor wings on their mericarps which are therefore dispersed by gravity alone. In the case of C. elegans, at least, it has been suggested that it evolved from epizoochorous ancestors that lost the spines because of the absence of suitable dispersing animals on the islands (Banasiak et al. 2016).

Though the carrot Daucus carota is perhaps the most widely grown daucine umbellifer, it is not the only economically significant member of the group. Cumin Cuminum cyminum, whose seeds are widely used as a spice, is either a daucine or a close relative of daucines (Banasiak et al. 2016). Cuminum does differ from other daucine genera in that its mericarps lack appendages on the secondary keels, however. Gladich Laser trilobum is a perennial found growing in Europe and western Asia whose seeds are used as a condiment. Certain species of the deadly carrot genus Thapsia have a history of medicinal usage though, as their vernacular name suggests, their use does require caution. One species, T. garganica, is among the suggested candidates for the identity of the mysterious silphium of the Romans (used, among other things, as an abortifacient) though perhaps not the most likely contender. That, perhaps, is a story for another time.

REFERENCES

Banasiak, Ł., A. Wojewódzka, J. Baczyński, J.-P. Reduron, M. Piwczyński, R. Kurzyna-Młynik, R. Gutaker, A. Czarnocka-Ciecura, S. Kosmala-Grzechnik & K. Spalik. 2016. Phylogeny of Apiaceae subtribe Daucinae and the taxonomic delineation of its genera. Taxon 65 (3): 563–585.

Wojewódzka, A., J. Baczyński, Ł. Banasiak, S. R. Downie, A. Czarnocka-Ciecura, M. Gierek, K. Frankiewicz & K. Spalik. 2019. Evolutionary shifts in fruit dispersal syndromes in Apiaceae tribe Scandiceae. Plant Systematics and Evolution 305: 401–414.

Five-fingers and Lancewoods

Longtime readers of this blog will know that my knowledge of plants has always been fairly rudimentary. As a young'un, I only ever learnt to distinguish some of the more common and visible varieties. As a student, I did take a few botany classes, but only really enough to learn that plant biology is complicated and terrifying. Since then, I've continued in much the same vein. But for today's post, I'm looking at something I do recall being aware of in my youth: the lancewoods and five-fingers of the genus Pseudopanax.

Horticultural variant of coastal five-finger Pseudopanax lessonii, copyright Leonora Enking.

Pseudopanax is a genus of a dozen species of small tree (mostly growing about five to seven metres in height) found only in New Zealand (Perrie & Shepherd 2009). Various species have also been assigned to the genus from locations around the Pacific (China, Tasmania, New Caledonia and Chile) but recent studies have lead to their exclusion. A handful of New Zealand species previously included in Pseudopanax have also been separated as the genus Raukaua (Mitchell et al. 1997). The historical taxonomy of the group is confusing, with species being variously attributed to genera Panax, Nothopanax, Neopanax and Polyscias. Things seem to have settled down a bit in recent years but there is still the possibility we may one day see Neopanax rise again (Perrie & Shepherd 2009).

Chatham Islands lancewood Pseudopanax chathamicus, copyright Krzysztof Ziarnek, Kenraiz.

Pseudopanax belongs to the family Araliaceae, a group that is primarily composed of tropical and subtropical shrubs and trees. Araliaceae are commonly referred to as "the ivy family", after one of their best-known members, the common ivy Hedera helix, but, as is not uncommon when a tropical family gets named after one of their European outliers, ivy is pretty weird by Araliaceae standards. Pseudopanax species are perhaps a bit more typical. They have large leaves, often more or less toothed or lobed along the margins. In a number of species, the leaves are palmately divided into three or five separate leaflets, hence the aforementioned vernacular name of 'five-finger'. In one group of species, the lancewoods, the lateral leaflets have been lost and the now undivided leaf is more or less long and narrow. Hybrids between five-fingers and lancewoods may have multiple leaflets like a five-finger but the leaflets shaped like those of a lancewood; New Zealand botanist Leon Perrie has written a post about hybridisation in this genus that you can read here. The trees are usually dioecious (male and female flowers are borne on separate trees) and the individually small flowers are borne aggregated in compound umbels. Fruits are fleshy berries.

Collection of lancewoods P. crassifolius showing the variation in leaf form, copyright Petra Gloyn. Two individuals on the left are young tress with hanging leaves; to the right is a more mature individual with spreading leaves.

Within Pseudopanax, the lancewoods are particularly renowned for their exhibition of heteroblasty, a phenomenon where the appearance of the leaves changes significantly as the tree matures. Juvenile leaves of the common lancewood P. crassifolius and toothed lancewood P. ferox are remarkably long, slender, strongly toothed along the margin, stiff and leathery, and hang downwards around the young tree like a skirt. As the tree approaches its mature height, it starts producing shorter, softer, less serrate leaves that are held in a more or less horizontal position.

Changes in growth habit with maturity seem to be surprisingly common among New Zealand plants and there has been a lot of discussion about why this might be. One suggestion that has certainly received a lot of public attention is that it is a relic of browsing by the large herbivorous birds such as moa that dominated the New Zealand environment prior to human settlement. Juvenile plants developed a habit that was energetically expensive but discouraged browsing by birds; as they grew high enough to escape the reach of such browsers, they changed to a less demanding form. I personally tend to be skeptical of these kinds of claims of historical baggage, not least because the extinction of one-half of the equation makes them very hard to test in any way, but I will admit that this case does perhaps have a bit more credibility than, for instance, claims elsewhere of giant fruits being dependent on long-extinct megafauna. Alternatively, it has been suggested that changes in growth habit may be related to climatic conditions; the juvenile leaves of P. crassifolius dissipate heat more effectively than those of mature trees (Gould 1993). Heteroblasty is less pronounced in the montane lancewood P. linearis of the South Island and almost absent in the Chatham Islands lancewood P. chathamicus, an insular derivative of P. crassifolius. Were these species insulated from the selective pressures affecting the other two? It should also be pointed out that the two proposals mentioned here are not mutually exclusive; the consideration of one as a factor does not automatically rule out the other.

REFERENCES

Gould, K. S. 1993. Leaf heteroblasty in Pseudopanax crassifolius: functional significance of leaf morphology and anatomy. Annals of Botany 71: 61–70.

Mitchell, A. D., D. G. Frodin & M. J. Heads. 1997. Reinstatement of Raukaua, a genus of the Araliaceae centred in New Zealand. New Zealand Journal of Botany 35 (3): 309–315.

Perrie, L. R., & L. D. Shepherd. 2009. Reconstructing the species phylogeny of Pseudopanax (Araliaceae), a genus of hybridising trees. Molecular Phylogenetics and Evolution 52: 774–783.

Australasian Mistletoes

Australia is home to a fair diversity of parasitic mistletoes, nearly ninety species in all. In a previous post, I described one of our most remarkable species, the terrestrial Nuytsia floribunda. But, of course, the remaining species occupy the more typical aerial mistletoe habitat, growing directly attached to the branches and trunk of their host. And within Australia, the most diverse mistletoe genus is Amyema.

Amyema pendula growing on Acacia, copyright Groogle.

Species of Amyema are found in southeast Asia, Australia, and islands of the Pacific as far east as Samoa. A revision of the genus by Barlow (1992) recognised 92 species with the greatest diversity in the Philippines, Australia and New Guinea. They are found in a range of habitats, from wet rainforests to arid woodlands. Some species (particularly in arid habitats) grow from a single central haustorium (the structure by which a parasitic plant attaches to and draws nutrients from its host); others (particularly rainforest species) produce numerous haustoria from runners stretching along the outside of the host. Most rainforest species tend to have low host specificity but those growin in arid habitats may be more likely to restrict themselves to a small number of host species. Those species which restrict themselves to a single host may have leaves closely resembling that host, making them difficult to spot within the host canopy.

Amyema species are mostly characterised by their flowers which are typical borne in triads with the triads often then being clustered in loose umbels. In some species, the triads are reduced to pairs or single flowers. The flowers themselves are bird-pollinated and have four to six long petals that are generally separated right to the base, at most forming only a very short tube at the base of the flower. The flowers are hermaphroditic though a study of some Australian species by Bernhardt et al. (1980) found a tendency for anthers to mature before the stigma, presumably to prevent self-pollination.

Flowers of Amyema miquelii, copyright Kevin Thiele.

Not surprisingly, attention on mistletoes in Australia has commonly been focused on their effect on host trees. Mistletoe infestations may be heavy and have commonly been blamed for tree mortalities. However, one might legitimately question whether mistletoes themselves cause fatalities: does mistletoe infestation cause a host tree to become unhealthy, or are unhealthy trees more vulnerable to infestation by mistletoes? A study by Reid et al. (1992) on Amyema preissii infesting Acacia victoriae found that, though there was a relationship between mistletoe volume and host mortality, they were unable to demonstrate that mistletoe removal improved host survival. Conversely, such a positive effect was found by Reid et al. (1994) for removal of Amyema miquelii growing on two Eucalyptus species (the methods of this latter study also include the great line, "the highest mistletoes had to be shot down with a .22 rifle"). However, the authors remained conservative when it came to advocating mistletoe removal. Not only do a number of native birds and other animals depend on mistletoes for food and nesting sites, mistletoe removal can be an expensive process and may not itself be devoid of adverse effects on the host tree. Where rates of infestation are not extreme, it may still be better to just live and let live.

REFERENCES

Barlow, B. A. 1992. Conspectus of the genus Amyema Tieghem (Loranthaceae). Blumea 36: 293–381.

Bernhardt, P., R. B. Knox & D. M. Calder. 1980. Floral biology and self-incompatibility in some Australian mistletoes of the genus Amyema (Loranthaceae). Australian Journal of Botany 28: 437–451.

Reid, N., D. M. Stafford Smith & W. N. Venables. 1992. Effect of mistletoes (Amyema preissii) on host (Acacia victoriae) survival. Australian Journal of Ecology 17: 219–222.

Reid, N., Z. Yan & J. Fittler. 1994. Impact of mistletoes (Amyema miquelii) on host (Eucalyptus blakelyi and Eucalyptus melliodora) survival and growth in temperate Australia. Forest Ecology and Management 70: 55–65.

White by Evening in the American Southwest

Though various species of it may be found around the world, the evening primrose family Onagraceae reaches its highest diversity in the south-west of North America. For this post, I'm looking at a genus endemic to this region, Eremothera.

Eremothera boothii, copyright Kerry Woods.

Eremothera is one of several genera of evening primroses newly recognised by Wagner et al. (2007). The species included in this genus had previously been included in the broader genera Oenothera or Camissonia, but these genera were progressively broken down owing to polyphyly and poor definitions. Eremothera species are annual herbs with more or less erect stems. Leaves are arranged on the stem alternately; those near the base are carried on a long petiole of up to six centimetres. The genus is distinguished from its close relatives by having mostly white flowers that open in the evening (in rare cases they my be pink or red, fading as they age). Pollination is by moths when the flowers first open, with small bees visiting the flowers the following morning. The fruit is a long capsule that arises directly from the main stem without a subtending stalk.

Eremothera refracta with flowers and green fruits, copyright Stan Shebs.

Seven species of Eremothera were recognised by Wagner et al. (2007). Eremothera nevadensis is a specialist of clay soil that occupies a relatively small range in Nevada, around Reno. Eremothera refracta is a widespread species in the south-west United States with fruit that are of an even diameter along their length (Hickman 1993). Eremothera chamaenerioides is a self-pollinating derivative of E. refracta with smaller flowers in which the stigma is surrounded and overtopped by the anthers. Eremothera boothii and E. minor (both also widespread) have fruits that are wider at the base than at the tip. In E. minor the inflorescence is held erect; in E. boothii the flowers nod. Two localised species, E. gouldii and E. pygmaea, are self-pollinating derivatives of E. boothii. Eremothera minor is also self-pollinating, and may in some cases even be cleistogamous with pollen being transferred to the stigma without the flower even opening.

REFERENCES

Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

Wagner, W. L., P. C. Hoch & P. H. Raven. 2007. Revised classification of the Onagraceae. Systematic Botany Monographs 83: 1–240.

A Slipper of the Lip

The world of flowering plants includes many unusual and eye-catching examples but even among all this variety the orchids often stand out. Their remarkable array of colours and forms have long fascinated people around the world. One of the more distinctive of orchid subgroups is the Cypripedioideae, commonly known as the slipper orchids.

Pink slipper orchids Cypripedium acaule, copyright Sasata.

Slipper orchids get their name from their most easily recognisable feature, a flower with a deeply saccate labellum or lip (the lower of the three petals) that is supposed to resemble a slipper (an analogy presumably settled on because the alternative of 'scrotum orchid' doesn't have the same ring to it). Like many other orchids, slipper orchids attract pollinators through deception rather than offering a genuine reward. Pollinators are enticed into entering the lip through its large central opening but find themselves unable to exit the same way (presumably because of the way that the rim of the opening curls inwards). Instead, they are forced to make their exit through one of two smaller openings at the base of the lip where it joins the flower's central column. As the pollinator exits this way, it must crawl past the stigma and stamens, removing any pollen it might already be carrying and depositing a new load.

Dwarf slipper orchid Cypripedium fargesii, copyright Steve Garvie.

The exact manner in which the pollinator is lured in varies by species and target (Pemberton 2013). Many produce odours that mimic legitimate nectar-producing flowers or potential food sources such as carrion. A group of species in the genus Cypripedium that are pollinated by bumble bees have low-growing flowers with a purple lip whose main opening appears black. They therefore resemble the opening of a mouse-hole of the type bumble bees use as nest sites. The North American Cypripedium fasciculatum produces a mushroom-like smell that attracts diapriid wasps that parasitise fungus gnats. Some species of the genus Paphiopedilum have light-coloured spots or warts on the flower that are mistaken for a colony of fat, healthy aphids by egg-laying hover flies seeking a food source for their larvae. Perhaps one of the oddest known set-ups is found in the species Cypripedium fargesii whose hover fly pollinator normally feeds on fungal spores. The orchid lures the fly in with patches of hairs on its leave that resemble a fungal infection. A few slipper orchid species are known to be habitually self-pollinating without the intervention of a pollinator; one such species, the South American Phragmipedium lindenii, has lost the slipper-shaped labellum and instead has a lip resembling the other petals.

Selenipedium dodsonii, a species only described as recently as 2015, copyright Andreas Kay.

Slipper orchids have been recognised as a distinct group from other orchids since at least 1840. A number of features isolate them from other orchids, such as their possession of two functional stamens (most other orchids have flowers with only a single stamen). More recent phylogenetic studies have corroborated their position as one of the earliest-diverging orchid lineages. Over 170 species of slipper orchid are currently known, divided by most authors between five genera; most of these genera have widely separated geographic ranges. The genera Selenipedium and Cypripedium have plicate leaves (that is, leaves that are folded within the bud several times longitudinally, in the manner of a fan) that are widely spaced along a well-developed stem, and a prominent rhizome (Rosso 1966). Selenipedium is a small genus found in northern South America that may reach heights of five metres. It differs from the more diverse Cypripedium in having trilocular ovaries and a commonly branching stem; Cypripedium, with over fifty species found across the Holarctic region, has unilocular ovaries and never branches. Cypripedium is the most widely distributed of the slipper orchid genera; the North American C. passerinum may even be found growing in tundra.

Paphiopedilum Leeanum, a cultivated hybrid originally developed in Britain in the 1880s, copyright David Eickhoff.

Phylogenetic analysis of the slipper orchids places Selenipedium as the sister group of the other genera with Cypripedium the next to diverge (Cox et al. 1997). The remaining three genera likely form a single clade united by the possession of a condensed rhizome and conduplicate leaves (folded once in the bud along the midline) arranged in a basal rosette. Paphiopedilum is the most speciose genus of slipper orchids with over ninety species found in India and southeastern Asia; it is also the genus most commonly found in cultivation. Phragmipedium includes over 25 species found in Central and South America; one of these, the Peruvian P. kovachii, has the largest known flowers of any slipper orchid, reaching twelve centimetres in diameter. The third genus Mexipedium, includes a single species M. xerophyticum found in Oaxaca state in Mexico. The three conduplicate-leaved genera are less distinct than the other two genera (one notable distinction is that Phragmipedium has trilocular ovaries whereas those of Paphiopedilum and Mexipedium are unilocular) and it has been suggested that they should be merged into a single genus. Nevertheless, not only are they all geographically distinct, they are supported as monophyletic by molecular analysis (Cox et al. 1997).

Phragmipedium caudatum, copyright Eric Hunt.

Their dramatic appearance has made slipper orchids highly prized in cultivation or by flower collectors. Unfortunately, many species have been subject to over-collection as a result. Many of the temperate Cypripedium species now require intensive conservation management, and populations of some Paphiopedilum species have been driven close to extinction. Once again, it would be a tragedy if such a fascinating group of plants was to vanish from the world.

REFERENCES

Cox, A. V., A. M. Pridgeon, V. A. Albert & M. W. Chase. 1997. Phylogenetics of the slipper orchids (Cypripedioideae, Orchidaceae): nuclear rDNA ITS sequences. Plant Systematics and Evolution 208: 197–223.

Pemberton, R. W. 2013. Pollination of slipper orchids (Cypripedioideae): a review. Lankesteriana 13 (1–2): 65–73.

Rosso, S. W. 1966. The vegetative anatomy of the Cypripedioideae (Orchidaceae). Journal of the Linnean Society, Botany 59: 309–341.

The Most Australian of Plants

Imagine yourself standing in a remote corner of northern Australia. Before you stretches an expanse of rolling hills, extending as far as the eye can see. The hills are covered with a carpet of green. You step forward, eager to explore these open fields. But as you approach them, everything changes. What appeared to be a uniform carpet is actually dense tussocks, each separated by an underlay of bare gravel. And instead of soft, yielding blades, the tussocks offer you nothing but resin and hate. Welcome to spinifex country.

Grassland dominated by Triodia pungens (bright green) and T. basedowii (grey-green), copyright Hesperian.

The spinifexes of the genus Triodia are a uniquely Australian group of plants. Some North American grasses have been assigned to this genus in the past but have since been moved elsewhere. There is also a widespread genus of coastal grasses that formally goes by the name of Spinifex but that is something different again. In many parts of arid Australia (and arid Australia equals most of Australia), spinifexes are the dominant form of plant life. As noted above, they grow in tight tussocks that may reach remarkable sizes and densities: clumps of the largest species may reach 2.5 metres in height and six metres in diameter (Lazarides 1997). Not uncommonly, these largest patches will be ring-shaped due to the centre dying off while growth continues around the edges. The leaf blades are long, needle-shaped, woody and rigid. Speaking from experience, the sharp tips of these blades will break off all too easily, embedding themselves in the flesh of any passers by. And some idea of their rigidity will also be conveyed by the fact that, in the growth season, it was not uncommon to discover macabre shish kebabs made from jumping grasshoppers that had had the misfortune to land on the end of one.

Mature stand of Triodia irritans, showing the tendency of hummocks to grow into circles as the centre dies off. Copyright ANBG photo M. Fagg.

Nearly 70 species are currently recognised within the genus, often differing in their preferred microhabitat. One of the most common species, Triodia basedowii, extends its range across almost the entirety of the continent between 18 and 30 degrees South and west of the Great Dividing Range. This species has a preference for sandplains and dunefields. Other species are far more localised. Barrett & Barrett (2011) described two new species found in association with sandstone cliff faces in the Ragged Range in Western Australia. Triodia barbata was found only in a thin band along the top of the cliff faces and may have had a population of only about 300 individuals. The more abundant (but still not widespread) T. cremnophila was found only on the vertical faces of the cliffs themselves. However, it must be noted that large gaps may exist in our knowledge of the ranges of Triodia species because of the remoteness and difficulty of getting to many of the regions in which they are found (seriously, if you've never been to central Australia yourself, it is difficult to appreciate just how much Absolutely Nothing there is there). Triodia mollis is known from two widely separated regions in northern Western Australia and Queensland with no confirmed records as yet from the entire expanse of the Northern Territory in between.

Preferred habitat of Triodia cremnophila, from Barrett & Barrett (2011). Yes, it only grows on the cliff face. Yes, someone presumably went down the cliff face to get specimens.

Being as woody and harsh as it is, it should come as no surprise that relatively few animals are capable of eating spinifex. Many Australian termites, such as the endemic genus Drepanotermes, are spinifex specialists; workers of Drepanotermes may be seen leaving their nest at night to collect pieces of spinifex blades and carry them back. Pastoralists may refer to 'hard' and 'soft' spinifex varieties but the difference is one of degree only; even the 'soft' spinifexes (usually the resin-producing species) are pretty damn hard by the standards of any other grass. Livestock are sometimes grazed on spinifex when bettter options are unavailable, in which case patches of spinifex may be burnt off to encourage the production of younger, more palatable growth (spinifex burns exceedingly well but also grows back readily from the remnant rootstock). The resin from spinifex also has a history of being used by indigenous Australians as an adhesive when making tools. For the most part, though, the main value of spinifex remains in its role as the dominant vegetation and habitat for the areas where it is found.

REFERENCES

Barrett, R. L., & M. D. Barrett. 2011. Two new species of Triodia (Poaceae: Triodieae) from the Kimberley region of Western Australia. Telopea 13 (1–2): 57–67.

Lazarides, M. 1997. A revision of Triodia including Plectrachne (Poaceae, Eragrostideae, Triodiinae). Australian Systematic Botany 10: 381–489.

Canterbury Bells

Bellflowers or harebells are one of the classic plants associated with the English country garden. For today's post, I'll be covering the family of plants that bellflowers belong to.

Fairy's thimble Campanula cochleariifolia, copyright Jerzy Opioła.

The Campanulaceae are a family of over 2300 plant species found almost worldwide (Crowl et al. 2016). The family is, however, divided between five subfamilies that some authors would treat as separate families, in which case 'Campanulaceae' would be restricted to the 600 or so species of the subfamily Campanuloideae. It is this subfamily that includes the bellflowers. The vernacular name, of course, refers to the shape of the flowers produced by these plants, as indeed does the botanical name: Campanula translates as 'little bell'. These flowers are radiately symmetrical with all petals more or less the same size and shape and evenly arranged in a circle. Other subfamilies of the Campanulaceae in the broad sense, the largest of which is the lobelias of the Lobelioideae, produce more bilaterally symmetrical flowers with petals differing in size and/or with some petals closer together than others. Fruits are most commonly a capsule, with the seeds dispersed by wind, but some lobelioids produce fleshy fruits that attract birds. The lobelioids are most diverse in the southern continents, and it is thought that this may have been the original home of the family as a whole when it arose sometime close to the end of the Cretaceous, possibly in Africa. At some time in the early Cenozoic, however, the campanuloids arrived in and underwent a significant radiation in the Palaearctic. This dispersal may be related to the different flower morphology of the campanuloids, as they adapted from the bird, bat and butterfly pollinators of the tropics to the bee and fly pollinators of more temperate habitats.

Glandular threadplant Nemacladus glanduliferus var. orientalis, copyright Stan Shebs.

The genetics of Campanulaceae, specifically of their chloroplasts, should also not go unnoticed. The structure of the chloroplast genome in plants is usually very stable, with few changes in gene arrangement and order. However, at various points in the history of Campunulaceae, large chunks of foreign DNA have been inserted in the original plastid chromosome, with a number of these insertions also associated with inversions in the direction of adjoining sections of the original genes (Knox 2014). This kind of insertion is unique among flowering plants: changes in the gene content of plastids more usually involve genes being transferred out of the plastid. The source of this extra DNA is uncertain: it may have come from the plant's own nucleus, or it may have come from an as-yet-unknown endosymbiont. Also unknown is the functional significance of these rearrangements, if any. Some insertions have clearly resulted in pseudogenes, with their sequences rapidly breaking down through subsequent genetic drift. But others have preserved the structure of functional genes, suggesting continued selection for their retention.

Cyanea duvalliorum, an arborescent Hawaiian lobeliad, copyright Forest & Kim Starr.

The majority of Campanulaceae are small perennial herbs. Two genera of distinctive enough to be assigned to their own subfamilies include annual herbs: the threadplants Nemacladus of southwestern North America, and the little-known Chilean Atacama desert endemic Cyphocarpus. Some members of the Lobelioideae are woody subshrubs, and at some point one of these woody lobelioids managed to make its way to the Hawaiian archipelago where it gave rise to one of the world's most remarkable insular radiations, and the single largest such radiation in plants. Over 120 species of lobeliads are known from the Hawaiian islands, varying from single-stemmed succulents to straggling vines to trees over 18 metres in height. There are inhabitants of lowland forests, of upland bogs, and of rocky cliffs. There are species producing fruit as dry capsules; others produce fleshy berries. So varied are the Hawaiian lobeliads that previous authors have inferred their origin from multiple seperate colonisations, but a study by Givnish et al. (2009) supported a single origin from a single colonist arriving about thirteen million years ago. This would have been before any of the current major Hawaiian islands existed (the oldest, Kaua'i, is a little less than five million years old); the implication is that the ancestor of the Hawaiian lobeliad arrived on a pre-existing island, perhaps corresponding to the modern Gardner Pinnacles or French Frigate Shoals. As the lobeliads diversified, they continued to disperse onto new islands as they arrived, while their original homeland eroded away.

Sadly, a depressing percentage of the species forming this incredible radiation are now threatened with extinction, the victims of pressures such as loss of habitat, the decline of their pollinators and dispersers, or grazing by introduced mammals. The cliff-dwelling pua 'ala Brighamia rockii of Moloka'i is now restricted to five locations with an estimated total wild population of less than 200 individuals. A related species on Kaua'i, the olulu Brighamia insignis, may be extinct in the wild, having last been recorded in the form of a single individual in 2014 (it still survives in cultivation). As we earlier saw with the Hawaiian honeycreepers, there is barely a single section of the Hawaiian biota not marked by tragedy.

REFERENCES

Crowl, A. A., N. W. Miles, C. J. Visger, K. Hansen, T. Ayers, R. Haberle & N. Cellinese. 2016. A global perspective on Campanulaceae: biogeographic, genomic, and floral evolution. American Journal of Botany 103 (2): 233–245.

Givnish, T. J., K. C. Millam, A. R. Mast, T. B. Paterson, T. J. Theim, A. L. Hipp, J. M. Henss, J. F. Smith, K. R. Wood & K. J. Sytsma. 2009. Origin, adaptive radiation and diversification of the Hawaiian lobeliads (Asterales: Campanulaceae). Proceedings of the Royal Society of London Series B—Biological Sciences 276: 407–416.

Knox, E. B. 2014. The dynamic history of plastid genomes in the Campanulaceae sensu lato is unique among angiosperms. Proceedings of the National Academy of Sciences of the USA 111 (30): 11097–11102.

Oily and Salty Trees

The Annonaceae is another one of those plant families like Acanthaceae that, despite containing a high diversity of speceis, tend to be overlooked because that diversity is mostly tropical. A number of species in the type genus Annona produce commercially significant fruits: custard apples, cherimoyas, soursops and the like. However, these are just a few of the 2400+ species of trees and lianes assigned to this family.

Ylang-ylang flowers Cananga odorata, from here.

Taxonomically, the Annonaceae is well established as distinct, readily recognised by a number of distinctive features. Among these is a characteristic 'cobweb' appearance to the wood structure when seen in cross-section, resulting from prominent rays of xylem connected by narrow cross-bands of parenchyma (Chatrou et al. 2012). Relationships within the family have been much harder to work out, not becoming well established until the advent of the molecular era. Recently, Chatrou et al. (2012) have recognised four subfamilies within the Annonaceae. The majority of species are placed in the subfamilies Annonoideae and Malmeoideae (which together form a clade), but a handful of species are placed in two basal subfamilies: one for the single genus Anaxagorea, and the Ambavioideae. Anaxagorea and the ambavioids differ from the annonoid-malmeoid clade in the structure of their seeds. Seeds of Annonaceae have what is called ruminate endosperm: that is, the surface of the endosperm is not smooth, but divided by wrinkles and grooves (the term 'ruminate' literally means 'chewed'). In Annonoideae and Malmeoideae, the ruminations of the endosperm are shaped like spines or lamellae. In Anaxagorea and the Ambavioideae, the ruminations are irregular in appearance. Molecular analyses place Anaxagorea as the sister taxon to all other Annonaceae.

View into the canopy of a salt-and-oil tree Cleistopholis patens, copyright Marco Schmidt.>

The Ambavioideae, despite not being very diverse, are widespread, with species found in the tropics of Africa, Asia and the Americas. Perhaps the best known ambavioid is the ylang-ylang tree Cananga odorata, native to south-east Asia, whose flowers are used as a source of perfume. Other south-east Asian ambavioids belong to the genera Cyathocalyx, Drepananthus and Mezzettia. The type genus, Ambavia, is native to Madagascar; other ambavioids in the genera Meiocarpidium, Cleistopholis and Lettowianthus are found in continental Africa. Finally, a single genus Tetrameranthus is found in South America. Most species of ambavioid are not systematically economically exploited but a number are locally used as sources of wood. The wood is light and not suitable for structural uses, but can be shaped and finished for utensils and other small items. The West African species Cleistopholis patens, whose Ghanaian name has been translated as 'salt and oil tree' (in reference to the taste of the bark when chewed), provides a fibrous bark that is readily stripped from the tree and is used for such purposes as matting and carrying straps (see here).

REFERENCES

Chatrou, L W., M. D. Pirie, R. H. J. Erkens, T. L. P. Couvreur, K. M. Neubig, J. R. Abbott, J. B. Mols, J. W. Maas, R. M. K. Saunders & M. W. Chase. 2012. A new subfamilial and tribal classification of the pantropical flowering plant family Annonaceae informed by molecular phylogenetics. Botanical Journal of the Linnean Society 169: 5–40.