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.