Evidence is provided for the first demonstrated example of allopolyploidy in the New Zealand fern flora. Cytological, morphological, and molecular (AFLP-DNA fingerprinting) analyses indicate that the fern previously known as Polystichum richardii constitutes an allopolyploid complex, in which four separate evolutionary lineages are present. These are here recognised as three taxonomic species, with one of these encompassing two subspecies. The two allooctoploid lineages are accommodated under the reinstated name P. neozelandicum, each as a separate subspecies: P. neozelandicum subsp. neozelandicum and the new combination P. neozelandicum subsp. zerophyllum. The new combination P. wawranum is made for one of the tetraploid lineages, while the name P. oculatum is reinstated for the other. Polystichum richardii is a later synonym of P. neozelandicum, and hence is not a legitimate name for any of the taxa recognised here.
Aim and location New Zealand began to separate from Gondwana c. 85 Ma, and has been isolated from the nearest large landmass, Australia, by some 2000 km of the Tasman Sea since c. 60 Ma. Given New Zealand's long geographical isolation, there has been considerable interest in explaining the origins of its different biotic elements. Here we investigate the biogeography of the fern genus Polystichum from temperate Australasia. Six species are found in New Zealand, four in Australia, and two on Lord Howe Island.
Methods The evolutionary relationships between the twelve Polystichum species found in temperate Australasia were inferred from phylogenetic analyses of two molecular data sets: DNA sequence from the chloroplast rps4–trnS spacer locus; and AFLP DNA‐fingerprinting. The timing of the separation between Australian and New Zealand Polystichum was estimated by using the fossil record to temporally calibrate the rbcL sequence differentiation between representative species from these regions.
Results Species of Polystichum from New Zealand appear to comprise a monophyletic group. This suggests that Polystichum crossed the Tasman only once. Temporal calibration of the rbcL sequence differentiation between Australian and New Zealand Polystichum indicates that a vicariant explanation for their separation can be rejected in favour of trans‐oceanic dispersal.
Main conclusions The extant diversity within New Zealand Polystichum appears to have been derived from a single, trans‐oceanic dispersal event (within the last c. 20 Myr), followed by a relatively extensive in situ ecological radiation.
Two polymorphic members of the Adiantum hispidulum Swartz complex, A. hispidulum sensu stricto and A. pubescens Schkuhr, have been critically studied on a morphological basis, utilising frond and hair forms, pinnule shape and size, soral features, number of sporangia per sorus, sporangial size, annulus position and number of indurated cells, spore shape and size, rhizome and stipe paleae. Separation of the two taxa is traditionally based on frond form (A. hispidulum being described as pinnate and A. pubescens as pedate), and indumentum characteristics (A. hispiqulum having medium to short stiff hairs, A. pubescens having long lax hairs). This study shows that only those characters associated with the pinnule hairs can be used to consistently separate the two taxa (A. hispidulum has short (63-815 /lm), stiff, often pigmented hairs with enlarged basal cells, while A. pubescens has long (251-1003 /lm), soft, pale hairs with narrow basal cells). However, even these characters showed a high degree of variability. Adiantum pubescens is given varietal status as A. hispidulum var pubescens.
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