Global review of recent taxonomic research into Isoetes (Isoetaceae), with implications for biogeography and conservation

With the advent of cytological analysis, Scanning Electron Microscopy, the recognition of sterile hybrids, improved access to wild populations and increasingly comprehensive molecular investigations, there has been a revolution in Isoetes taxonomy in recent times. The last 40 years have seen an almost 100% increase in the diversity documented during the previous two centuries. Four geographic areas account for over 90% of this diversity: northern-central South America, eastern North America, western Eurasia (including the northern Mediterranean) and South to Tropical Africa. There is a significant global conservation concern for Isoetes, with many taxa being rare (known from one to a handful of populations) and some known only from herbarium specimens. The taxa of the extraordinary rock-outcrop pools and the ephemeral wetlands found in disjunct areas around the world appear to be particularly vulnerable to habitat destruction. We expect 100 or more new taxa to be described in coming years. Such taxonomic productivity will require more systematic cytological and molecular investigations to be undertaken. It also requires the assembly of a larger global inventory of high-quality voucher specimens to provide the material for such investigations.