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Botany Photo of the Day
In science, beauty. In beauty, science. Daily.

Oct 18, 2014: Fothergilla major

Before starting today's entry, a note to local readers -- there are still many apple varieties available for the second day of the Apple Festival tomorrow, including one of my favourites, the Salish apple.

Thank you again to Martin Deasy for guest-writing and photographing a series on the Hamamelidaceae. Martin, who trained at the Royal Botanic Gardens, Kew in its Kew Diploma in Horticulture program, concludes the series with this entry.

The bottlebrush-like inflorescences of Fothergilla major--unlike anything else in the Hamamelidaceae--are just one more example of the family's remarkable diversity of floral morphology. As with Parrotiopsis, what look like flowers are in fact pseudanthia--compound inflorescences that "mimic" individual flowers. What appear to be petals are in fact clavate (club-like) stamens with inflated filaments, up to 32 in each flower; numerous reduced flowers are packed together on a rachis to form a single inflorescence.

An upland species native to the highlands of the southeast U.S.A. (the Appalachians of North Carolina and Tennessee), Fothergilla major occurs at altitudes of up to 1000m, particularly on dry ridges. It grows into a small deciduous tree, to ca. 5m, often suckering from underground stems to form dense thickets. The relatively late (for the family) anthesis in late April-May likely represents an adaptation to the harsher climate at altitude (the other Fothergilla species--the less hardy Fothergilla gardenii--is restricted to the coastal plain of the south-eastern U.S., and flowers in mid-April).

Absence of petals is an inherited trait (symplesiomorphy) of tribe Fothergilleae, whose members exhibit a progression from insect- to wind-pollination. The two insect-pollinated taxa, Fothergilla and Parrotiopsis, are also both the most basal; the more derived taxa (respectively Parrotia, Sycopsis, Distylium and Distyliopsis) have adopted wind as the principal means of pollination.

The comparison of Fothergilla and Parrotiopsis is revealing: the two genera are extremely closely related; yet each has recruited a different organ as attractant, lending their inflorescences radically different appearances. Nevertheless, the infructescences are very similar--indeed fruit morphology is astonishingly highly conserved across the entire Hamamelidoideae, a subject for a future post.

Oct 17, 2014: Malus 'Belle de Boskoop'

Malus 'Belle de Boskoop'

It's that time of year again--UBC Botanical Garden is hosting its annual Apple Festival this weekend. Like most previous years on BPotD, we're highlighting one of the 70+ apple cultivars available for sale (more for tasting and viewing). This year's image is similar, but different, to the one that Taisha did last year of Malus 'Okana'. Other previous entries: 'Rubinette', 'Creston', SPA493 (now known under the trade name Salish, one of my favourites), 'Cox's Orange Pippin', 'Golden Russet', 'Melrose', 'Elstar', and 'Jonagold'.

'Belle de Boskoop' has been in cultivation for over 150 years, originating as a chance seedling in or near the horticulturally-famous Boskoop, a town in The Netherlands. I don't have any personal experience with this cultivar, other than tasting it today. I would like to say it is "out of this world" given the concept behind today's image, but though I liked the acidity of the apple, the texture was a bit soft for me. From what sources suggest online, the edibility improves over time--time which one has, as it keeps for up to 6 months, with the flavour improving as it ages. My understanding from speaking with some of the Friends of the Garden is that it is also a very popular seller to people who grew up in northern Europe (in fact, one Danish commenter on another site mentions, "This is not considered an eating apple, but THE cooking apple for much of northern continental europe." Read a review, plus this comment and many others here: 'Belle de Boskoop' on Adam's Apples). To read more thoughts, also check out this 'Belle de Boskoop' review on The Fruit Gardener weblog (and additional comments).

There perhaps might be some questions about how today's photograph was done. The photo was taken from inside my office, using external flash units for much of the lighting. The flash looks overdone for my taste, but dialing the flash down or adjusting the position of the flash units in order to create shadows on the surface of the apples resulted in the rain-droplet "stars" on the window pane being diminished, so choices were made. I would have preferred to have also gotten the shadow across the body of the apple effect that Taisha succeeded with in the 'Okana' photograph, but I think I would had to have made an exposure for that and an exposure for the background, then blended the two images together. As it is, the image-editing program was used to remove the narrow supports below the apples (which I also taped to the glass to stay in place).

Oct 16, 2014: Sinowilsonia henryi

Sinowilsonia henryi

Martin Deasy's series on the Hamamelidaceae continues today with its fourth entry. The fifth, and final entry, will appear on Saturday. Martin writes:

The monotypic genus Sinowilsonia is named for the prolific English plant hunter E. H. "Chinese" Wilson, immortalizing both his surname and his nickname (the prefix "sino-" means "pertaining to China"). The species was first collected for Western science from the wild in 1889 by the remarkable Irish plantsman Augustine Henry, and bears his name. The original herbarium voucher specimen he sent to Kew can be viewed digitally (or see Wilson's 1907 collection of the same species).

Sinowilsonia henryi is a medium-sized tree native to the mixed forests of central China. Its unisexual inflorescences--effectively a type of catkin--are numerous and highly distinctive. Both male and female catkins are ca. 5cm long at pollination, but the rachis of the female inflorescence elongates markedly after fertilization, attaining a final length of 20cm or more.

The photograph shows a fertilized female inflorescence in the process of elongating. Each flower bears twin pinkish-green styles and 5 greenish sepals on a swelling pistil. Sporadic rusty-brown stellate trichomes (a familiar Hamamelidaceae character) are also visible on close inspection. Adjacent are the exhausted male catkins, beginning to dessicate having released their pollen some time earlier.

Sinowilsonia's reduced flowers (lacking petals and either male or female sexual parts) are typical of wind-pollinated taxa, which do not require petals to attract pollinators, but instead need to produce large volumes of pollen to maximize the chances of fertilization.

The characteristic inflorescences of Sinowilsonia (together with those of the other anemophilous Hamamelidaceae genera Sycopsis, Distylium and Parrotia) give some insight into why the Hamamelidaceae were historically closely aligned with other families of wind-pollinated catkin-bearers (the artificial grouping dubbed the Amentiferae). Systems such as that of Engler & Prantl treated them as neighbours to e.g. Fagaceae, Betulaceae, Juglandaceae, Urticaceae and Platanaceae, and despite almost immediate dissent, these relationships proved surprisingly slow to be dismantled.

More sophisticated morphological, and later molecular, taxonomy made clear that the reduced flowers found in wind-pollinated catkins were highly derived--that is, they did not represent a "primitive" ancestral state, and were therefore of little use in drawing conclusions about evolutionary relationships between taxa. Fragments of the Amentiferae are now widely scattered within the Fagales, Rosales and even Proteales. The Hamamelidaceae, meanwhile, are located firmly within order Saxifragales (the apically unfused bicarpellate pistils, and twin styles, are highly diagnostic).

In fact, within the Hamamelidaceae alone, wind pollination has evolved several times, in each case from an ancestral state of insect pollination. Thus most of Hamamelidaceae's anemophilous genera are found within tribe Fothergilleae, whereas Sinowilsonia has evolved separately within tribe Eustigmateae.

Oct 15, 2014: Hamamelis virginiana

Hamamelis virginiana

Today, we have the third in the series on Hamamelidaceae guest-written and photographed by Martin Deasy. Martin writes:

The sight of Hamamelis virginiana with its tangle of bare twigs covered in yellow blossom is one of the most striking sights of the late autumn and early winter. Widely distributed in the deciduous forests of eastern North America, it forms a small, spreading tree with small branches. It is well known as the source of the witch hazel extract widely used as an astringent, obtained from a decoction of the stems.

Assigned its own tribe (Hamamelideae) within subfamily Hamamelidoideae, the genus Hamamelis is characterized by strictly 4-merous, hermaphrodite flowers, with long, ribbon-like petals that are circinate (rolled like a fire-hose) in bud. A whorl of 4 staminodes secrete a nectar reward for pollinators. The anthers have only one sporangium per theca, and each theca opens outwards by a single valve, rather as if the anther were releasing its pollen through a pair of car doors.

Unlike other Hamamelis species, which flower from late winter into early spring, Hamamelis virginiana flowers in the autumn, from October until Christmas (in the northern hemisphere), and is pollinated by insects (mainly small flies). Following pollination, the pollen tube penetrates downwards towards the base of the carpel, at which stage it ceases development and overwinters before growth is recommenced--and the ovule fertilized--in late spring. There is thus a delay between pollination and fertilization of up to 7 months.

A possible explanation for Hamamelis virginiana's eccentric phenology (flowering period) has been suggested by observations from the Ozark mountains, where the species overlaps in range with the later flowering Hamamelis vernalis. In unusual years in which both taxa flowered simultaneously, it was observed that, given the choice, insect pollinators strongly favoured Hamamelis vernalis. This raises the possibility that the displacement of its flowering period into the late autumn might represent an adaptive strategy allowing Hamamelis virginiana to avoid having to compete for pollinators with its more appealing relation. Even then, relying on insect pollinators during the coldest parts of the year proves very inefficient , one study finding the rate of fruit set to be less than 1% (ref: Anderson and Hill 2002).

The issue of the numerous disjunct distributions characteristic of the Hamamelidaceae has already been partly treated in yesterday's post on Trichocladus crinitus. Hamamelis offers another particularly good example. Of the five Hamamelis species, three are from eastern North America, while two are east Asian--the classic "Tertiary Relict" disjunct distribution that has fascinated and teased botanists since it was first noticed in the 18th century. As the climate cooled in the Oligocene (ca. 35mya-23mya), the high-latitude Tertiary flora seems gradually to have been forced southwards, ultimately into its present-day refuges of either eastern Asia or southeastern North America.

The original geographical area occupied by the northern Tertiary flora included territory now submerged beneath the Pacific, Atlantic and Arctic oceans--the so-called "land bridges" (though they should not be thought of as mere bridges: they constituted fairly permanent land in their own right). Asia and North America have historically been connected by a substantial landmass known as Beringia, and it seems plausible that the extant Hamamelis species may have differentiated from an ancestral population present in or around Beringia. In this context, it is striking that the Japanese hamamelis (Hamamelis japonica, from the islands of southern Japan) is more closely related to the American species than to the Chinese Hamamelis mollis.

Oct 14, 2014: Trichocladus crinitus

A continuation of the series guest-written and photographed by Martin Deasy, who is a British horticulturist based in Oxford, England. Martin writes:

The startlingly furry appearance of Trichocladus crinitus, or black witch-hazel, is caused by the presence of rusty-brown stellate trichomes (or hairs). These are a feature of practically all Hamamelidaceae species, but here are closely packed to form an unusually dense indumentum. The resemblance of the unexpanded opposite (or sub-opposite) leaves to pairs of rabbits' ears only emphasizes the impression of animal fur.

Trichocladus crinitus is endemic to the moist Afromontane forests of South Africa, where it is locally dominant as a constituent of the understory vegetation--the Afrikaans name onderbos translates literally as "undergrowth." The plant forms a large, rather open shrub or small tree up to 3m in height, and its hard, white wood gives it its local Xhosa name iThambo ("bone").

The tiny flowers are packed together in dense spherical heads. The photo shows flowers before and after the anthers have dehisced. The floral features can be easily made out: 5 green sepals with rusty-brown stellate trichomes on the outer (abaxial) surfaces, and 5 pale-pink petals with involute margins and stellate pubescence, again on the abaxial surface. The 5 pale pink stamens, and twin styles (green) can also be seen. The anthers release their pollen in an unusual manner: although the anthers are tetrasporangiate, each theca opens with a single valve.

Trichocladus crinitus is one of five species in a genus distributed from Ethiopia, down through East Africa to the Cape, and offers an interesting case study in biogeography and floristics. Early accounts of Trichocladus (e.g. Hutchinson 1933) noted its longitudinal north-south distribution on the continent, inferring dispersal into Africa southwards from an ancestral range in Eurasia.

However, it was subsequently noticed that Trichocladus's highly unusual mode of anther dehiscence--rare even among the rest of the angiosperms--is shared with a handful of Hamamelidaceae species restricted to Australia, Madagascar and Africa. Dubbed the "Southern Hamamelidaceae" (Endress 1989), the close genetic relationship of this group was subsequently confirmed by molecular studies, and circumscribed as tribe Dicorypheae (Li & Bogle 2001). The five constituent taxa are Noahdendron, Ostrearia, Neostrearia (Australia), Dicoryphe (Madagascar) and Trichocladus (Africa).

The disjunct distribution of the Dicorypheae aroused some interest, since the locations in which they occur map onto the remnants of the supercontinent Gondwanaland, which after an existence of several hundred million years, broke up in stages between 165mya and 50mya. The existence of a disjunct subgroup of closely-related and highly distinctive hamamelid taxa on vestigial Gondwanan landmasses suggested that the Dicorypheae may have originated in Gondwana, the surviving members arriving in their present situations by continental drift (or vicariance, to use the technical term).

The Hamamelidaceae is known to be an ancient clade (the fossil record dates back to at least the late Cretaceous, ca. 85mya), so this posited Gondwanan lineage was quite plausible. However, it would have made the Hamamelidaceae an exceptionally ancient angiosperm lineage, pushing the original diversification of the family well back into the mid-Cretaceous, prior to the disintegration of Eastern Gondwana.

Subsequent work has shown that the apparent Gondwanan distribution is a red herring. Tellingly, the Australian taxa occur in the extreme northeastern corner of the continent closest to Asia, where the relict Gondwanan rainforest was infiltrated by Asian taxa during the Miocene (5.4mya), when the collision of the Australian and Southeast Asian continental plates facilitated significant floristic exchange. Furthermore, molecular evidence has revealed the Dicorypheae to be embedded within a larger clade of overwhelmingly pan-Asian distribution, strongly indicating that the "Southern Hamamelidaceae" differentiated in Asia, arriving at their present positions by a process of dispersal.

Fossil evidence of Hamamelidaceae species from Antarctica--another Gondwanan remnant--might seem to throw a spanner in the works. But reports of fossil Hamamelidaceae pollen at Antarctic sites invariably turn out to refer to Altingiaceae, now split off as a separate family. In fact, the story of Trichocladus's evaporating Gondwanan history recapitulates an increasingly familiar narrative in which molecular dating techniques demonstrate that putative Gondwanan distributions actually result from much later dispersals out of the northern hemisphere (cf. Davis et al. 2002).

The plant shown grew for many years in the remarkable Temperate House at the Royal Botanic Gardens, Kew--the world's largest surviving nineteenth-century glasshouse. The House is currently undergoing a major restoration, and most plants (with the exception of a few large palms) have been moved to temporary quarters for the duration of the five-year renovation project due to be completed in 2018.

Oct 10, 2014: Parrotiopsis jacquemontiana

We start a series today guest-written and photographed by Martin Deasy, who is a British horticulturist based in Oxford, England. Martin trained at the Royal Botanic Gardens, Kew, where he spent three years studying for the Kew Diploma in Horticulture. Martin writes:

This is the first in a 5-part series on the witch hazel family (Hamamelidaceae), focusing mainly on subfamily Hamamelidoideae, the largest and best resolved of Hamamelidaceae's five subfamilies. The classification adopted is that of Li and Bogle (2001).

For a relatively small family (±140 species in 31 genera), the Hamamelidaceae exhibits remarkable diversity in floral structure and pollination syndromes. Most people will be familiar with the characteristic flowers of the common (American) witch hazel, Hamamelis virginiana (Daniel adds: or, similar to it, Hamamelis mollis), with its heads of 4-petalled, strap-like, fly-pollinated flowers. However, other Hamamelidaceae genera have very different blooms. Today's photo shows the pseudanthial inflorescence of Parrotiopsis jacquemontiana, in which the "flower" is in fact a compound floral structure imitating the appearance of an individual flower.

Parrotiopsis belongs to tribe Fothergilleae, which is characterized by the absence of petals. In this striking but rarely cultivated species, what look like "petals" are in fact white bracts inserted on the peduncle below the inflorescence. The central yellow head comprises numerous hermaphrodite flowers, each with ±15 stamens and a bifid style mounted on a tomentose ovary; the tiny sepals are scarcely visible, and petals are absent entirely.

Parrotiopsis jacquemontiana--the only member of the genus--is native to the northwestern Himalaya (India, Pakistan, Afghanistan), and forms a small, compact tree. Its sturdy wood is used to make walking sticks and furniture, while the pliable twigs are used for weaving baskets. The plant shown grows at the Royal Botanic Gardens, Kew (UK), from seed collected in 1983 in the Swat Valley, Pakistan, on a west-facing scree slope at 2700m-2980m.

The floral diversity of the Hamamelidaceae reflects the family's ancient lineage and widespread distribution (the family has been present on every continent except Antarctica, though glaciation wiped it out of Europe). The great age of this group of plants means that closely related genera have persisted in isolation thousands of kilometres--or even continents--apart. Since the evolution of pseudanthia represents a relatively local adaptation to specific pollinators, inflorescence morphology can vary even between closely related genera. Thus although most of tribe Fothergilleae are wind-pollinated (e.g. Parrotia, Sycopsis, Distylium), their close relations Fothergilla and Parrotiopsis are pollinated by insects. The only bird-pollinated hamamelid genus, the distantly related eastern Asian Rhodoleia, likewise has a pseudanthial inflorescence.

Oct 8, 2014: Clivia caulescens and Clivia miniata

Today's entry was written by Tamara, who scribes:

For this BPotD entry, I chose to compare two species of Clivia in order to highlight how one species in a group has evolved to use a different set of pollinators. Thank you to the late James Gaither (aka J.G. in S.F.@Flickr) for his photo of Clivia caulescens taken at the San Francisco Botanical Garden, and to Priscilla Burcher (Priscilla Burcher@Flickr) for her image of Clivia miniata taken at the Walter Sisulu National Botanical Garden in South Africa.

Clivias are endemic to South Africa and Swaziland. These yellow, orange, or red-flowering plants have been popular ornamental species in Western gardens since they were first collected by the British explorers William Burchell and John Bowie in the early 19th century. Clivias have long, dark-green strap-shaped leaves and are adapted to the low-light conditions of the forest floor. They have been extensively bred for ornamental qualities, and even have a global fan base (check out the Global Clivia Enthusiast Forum if you also share this passion). Clivia miniata is the most-cultivated of the genus, commonly called Natal lily or bush lily. It reaches a height of about 45 cm, and in its native habitat grows in well-drained, humus-rich soil of forest floors or, rarely, in the fork of a tree. Clivia caulescens is rarely cultivated. This species has an unusual stem for a Clivia, which reaches to 90cm in height with aerial roots along its length.

Natal lily is the only Clivia that is pollinated by butterflies, while Clivia caulescens, like all other species of Clivia, is pollinated by sunbirds. The botanists Ian Kiepiel and Steven D. Johnson, in the 2013 article Shift from Bird to Butterfly Pollination in Clivia assert that the ancestor of Natal lily was a sunbird-pollinated species like the other members of the genus. In the evolution of Clivia miniata, a transition to butterfly pollination occurred. One of the most pronounced shifts found by Kiepel and Johnson was that the flowers went from the pendulous, tubular flowers exemplified by today's image of Clivia caulescens to the upright, trumpet-shaped flowers of Clivia miniata. This change is best explained by examining the pollinating methods of sunbirds compared to butterflies. Sunbirds desire a perch while consuming their nectar, and the drooping flowers of Clivia caulescens allow these birds to perch on the flower stem and probe upwards for the nectar. Upright flowers, on the other hand, are nearly impossible for these birds to reach when perched on the stem. Rather than a perch, butterflies need a landing pad, which the upward-facing flowers of Clivia miniata provide. Upwards-facing flowers also allow the species to take advantage of butterflies that brush past as they explore and claim territory, collecting pollen on their wings and dispersing it onto the upright stamens. Kiepel and Johnson point out that these flower forms are similar to those found in other genera pollinated by either sunbirds or butterflies, respectively.

Other differences in flower physiology include lower pollen production and greater scent in Natal lily than in other members of the genus; birds require a greater amount of pollen than butterflies do, and rely much less on their sense of smell. The characteristics that did not change when the species shifted its pollination strategy are as interesting as those that did. Flower colour - a vibrant orange-red possessing a high UV reflectance, is the same for the sunbird and butterfly-pollinated clivias. Sunbirds and butterflies both have UV receptors, and are likely to be able to perceive the clivias in a very similar fashion. It is likely that this similarity in visual perception is one of the factors that made the change in pollinators possible. In case you want to know what a Clivia miniata flower looks like to a sunbird or butterfly, see Dr. Klaus Schmitt's image on the Photography of the Invisible World site.

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