Species Delimitation in Sciadocladus (Pterobryellaceae, Bryophyta)

Sciadocladus is a distinctive genus of large dendroid mosses restricted to New Zealand, New Caledonia and the Solomon Islands. Of the two extant species, S. kerrii is endemic to New Zealand, while S. menziesii is found in New Zealand, New Caledonia and the Solomon Islands. Populations of S. menziesii from New Caledonia and the Solomons have been recognised as subspecies splendidum, distinct from the New Zealand populations. Given the geographical isolation of the two subspecies of S. menziesii, we hypothesised that the endemic S. kerrii could have arisen in situ in New Zealand through speciation from S. menziesii subsp. menziesii. This would make these two taxa more closely related to each other than S. menziesii subsp. menziesii is to S. menziesii subsp. splendidum, challenging the species concept of S. menziesii. We tested this hypothesis by conducting a phylogenetic analysis of molecular data from multiple exemplars of Sciadocladus, including material from both New Zealand and New Caledonia. The results show all specimens of S. menziesii strongly supported as monophyletic, sister to a clade comprising S. kerrii specimens, thus rejecting the hypothesis and corroborating the established taxonomy. Implications for interpretation of the phylogeographic history of the genus are discussed.