Field of Science

Time to update my taxonomy and yours - Clubmosses

This is not a continuation of bryophyte seek; clubmosses are vascular plants. In fact clubmosses are the oldest lineage of vascular land plants, and those that exist today are sadly mere relicts of past diversity. Their taxonomy used to be pretty easy, and you only had to know a handful of genera, but splitters have been at work, whether justified or unjustified, and now the Phactor must learn some new names. Bother. Now Selaginella is not a particular problem, and as the oldest living genus, it’s taxonomy is pretty well behaved, but not so with Lycopodium. Quite a number of its species have been transferred to other genera. First, Lycopodium (top) now consists of those species of clubmoss that have aerial shoots arising from a rhizome, bristly leaves arranged helically along an axis, and sporangia borne apically in distinct strobili, cones. Some 10-15 temperate to Arctic species that lack a rhizome and bear sporangia along the axis subtended by unmodified, or largely so, leaves, and therefore lack terminal strobili, are now in the genus Huperzia (middle - Image credit Dave Webb via the BSA). And then there’s Diphasiastrum (3d image) which by having scale-like, over-lapping leaves along the stems making them look rather flattened. Tropical species of Lycopodium that are largely epiphytic, but lacking a rhizome more or less befitting their growth habit, are now called Phlegmaria (bottom - image credit: Heaton's Ferns). Careful how you say it.

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