Aspleniumhybrids in the New Zealand flora

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Abstract
Nineteen different inter-specific or inter-subspecific Asplenium hybrids occurring naturally in the New Zealand flora are described and illustrated. All produce shrivelled and aborted spores and are therefore thought to be largely sterile. Other hybrid combinations almost certainly occur, especially between different cytotypes of polymorphic species aggregates, but they require cytological detection and cannot be recognised by their morphological characteristics alone. The capacity for hybridisation varies considerably from species to species; some such as A. flaccidum, A. bulbiferum, and A. terrestre hybridise quite frequently, but others such as A. polyodon and A. trichomanes are not known to form hybrids in New Zealand. Possible reasons for this are discussed. Considerable taxonomic complexity results from the remarkable cross-compatibility of New Zealand Asplenium species, but introgressive hybridisation is thought to be of only minor importance due to the sterility of the inter-specific hybrids. The evolutionary importance of this finding is discussed in relation to the development of the New Zealand Asplenium flora. Cytological evidence from the hybrid A. flaccidum subsp. flaccidum × terrestre subsp. maritimum suggests that A. terrestre may be an autopolyploid derivative of A. flaccidum. A possible auto- or allopolyploid origin for all the other higher polyploid species is outlined as a basis for future cytogenetic investigation of the genus.