The genus Trichomanes L. (sensu lato) is predominantly distributed in the tropics and sub-tropics, with rare and scattered occurrences in northern temperate regions. A single species, T. speciosum Willd., is native to Europe and has been considered one of the continent’s most threatened pteridophytes. This Macaronesian-European endemic is allied to, and the ecological equivalent of, the North American T. boschianum Stürm. The sporophyte generation of T. speciosum occurs as scattered individuals at widely disjunct sites along the western seaboard of Europe, extending as far north as Scotland and only achieving local abundance on the Atlantic Islands (Madeira and the Azores). In Macaronesia the species reproductive behaviour can be considered “normal”, whereas further north, where cooler, and east, where drier, reproductive success progressively declines and sporophyte mortality increases. Over much of the British Isles and continental Europe only the gametophyte generation survives. Are these widely disjunct populations Tertiary, or earlier, relicts, or post-glacial colonists, and if the latter from which refugial areas had they colonised? We have investigated genetic diversity (allozymes and DNA) throughout the species range to address these questions and to determine what proportion of the diversity is held in the respective generations and whether variation private to the independent gametophytes should be considered “lost” because of their “asexual” nature. Gametophyte populations of this species can be considered as a comparatively invulnerable repository of variation, akin to a vast “seed-bank”, which retains the potential to reproduce sexually given a changed climatic regime. The parallels and contrasts with the situation in North America are considered.

Key words: allozymes, colonisation patterns, independent gametophyte, phylogeography, Trichomanes