Abstract
Twenty-nine populations of three closely related taxa, Asplenium lepidum, A. haussknecktii and A. samarkandense, have been raised together in cultivation. There is considerable inter-population variation, and the ranges of variation of the three species overlap. Cytogenetic investigation of artificial hybrids has shown that the three taxa are all allotetraploid and that they share the same diploid parents, A. aegaeum and A. ruta-muraria subsp. dolomiticum. Analysis of F1 and F2 hybrids between different populations indicates high inter-fertility. The aggregate is re-defined as a single polymorphic species (A. lepidum) consisting of two subspecies (subsp. lepidum and subsp. haussknechtii) distinguished primarily by gland and sporangial characters. A. samarkandense is reduced to a variety of subsp. haussknechtii. It is suggested that the two subspecies have had separate geographical origins from different morphological variants of the same diploid parents, but the polymorphic nature of the aggregate is principally due to divergent evolution in small populations isolated on limestone mountains in southern Europe and western Asia.
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