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.