Tmesipteris horomaka, a new octoploid species from Banks Peninsula

Tmesipteris horomaka sp. nov. is a rare octoploid, endemic to Banks Peninsula, New Zealand. It is morphologically intermediate between the tetraploids Tmesipteris elongata and Tmesipteris tannensis, and is possibly their allopolyploid derivative. DNA sequences from the trnL-trnF locus of the uniparentally inherited chloroplast support T. elongata as a progenitor, but direct evidence for T. tannensis is lacking. Tmesipteris horomaka differs from T. elongata in having predominantly emarginate to truncate leaf apices, and from T. tannensis in having synangia that are more rounded in shape, lacking or with only slight points that are directed laterally, rather than being clearly biconic with the points directed upwards away from the subtending leaf. Tmesipteris horomaka generally has bigger spores than both T. elongata and T. tannensis. We suggest that T. horomaka be treated in the Threat Classification System as Nationally Critical DP, OL, this being based on the small number of tree fern hosts on which it is currently known to grow.