The origin, status and distribution of Asplenium presolanense spec. nov. (Aspleniaceae, Pteridophyta)

The origin, status and distribution of the allotetraploid Asplenium presola nense have been investigated. This taxon was described as a calcicole subsp ecies of A.. adulterinum, discriminated as much by its ecology as its morph ology. Asplenium adulterinum s. str. is a small allotetraploid rock fern wi th a scattered, but widespread, distribution in Europe growing nearly exclu sively on serpentine and other ultrabasic rocks. Asplenium presolanense was reported from three sites, one population of c. 30 plants on limestone at Presolana in the Bergamo Alps, Italy, one population of five plants on mica schist in Val di Gag (Poschiavo, Switzerland, some 35 km north) and several populations on limestone on Vancouver Island, Canada. Our evidence from mo rphological comparison, allozyme electrophoresis and length polymorphism in a non-coding spacer on the chloroplast DNA suggests that these three popul ations of putative A. presolanense represent two different taxa. The plants from Switzerland and Canada are shown to be A. adulterinum s. str., the al lotetraploid derived from diploid A. viride and diploid A. trichomanes subs p. trichomanes. The taxon from Presolana is considered to merit specific st atus as A. presolanense as it is of distinct origin. Calcifuge A. trichoman es subsp. trichomanes is not involved but, instead, the calcicole diploid A . trichomanes subsp. inexpectans is postulated to be the other parental tax on. Genetic evidence suggests that A. presolanense is an apoendemic taxon.