Overview
Most of New Zealand's spleenwort Asplenium ferns are closely related and belong to the "Austral" group, which is common in Australasia.
Many of these Austral species hybridise, making their identification sometimes difficult. Although the hybrids are sterile, they look intermediate between their parents and blur their distinctiveness.
About half of the Austral species in New Zealand have double the number of chromosomes, known as polyploidy. Polyploidy often involves hybridisation. For example, Asplenium gracillimum is a polyploid derived from hybridisation between A. bulbiferum and A. hookerianum.
The four species in New Zealand that are not part of the Austral group are Asplenium flabellifolium, A. pauperequitum, A. polyodon, and A. trichomanes.
For more information, see the following references:
Perrie LR, Brownsey PJ (2005) Insights into the Biogeography and Polyploid Evolution of New Zealand Asplenium from Chloroplast DNA Sequence Data. American Fern Journal 95: 1-21.
Shepherd LD, Holland BR, Perrie LR (2008) Conflict amongst chloroplast DNA sequences obscures the phylogeny of a group of Asplenium ferns. Molecular Phylogenetics and Evolution 48: 176-187.
Shepherd LD, Perrie LR, Brownsey PJ (2008) Low-copy nuclear DNA sequences reveal a predominance of allopolyploids in a New Zealand Asplenium fern complex. Molecular Phylogenetics and Evolution 49: 240-248.