A taxonomic re-evaluation of Pittosporum roimata Gemmill & S.N. Carter (Pittosporaceae, Apiales)

Abstract

Pittosporum roimata Gemmill & S.N. Carter (Pittosporaceae, Apiales) was established in 2018 as an endemic species confined to the Poor Knights Islands group, off the eastern coastline of Northland Aotearoa / New Zealand. The new species was distinguished from P. cornifolium A. Cunn. on the basis of vegetative characters (leaf length, width, petiole length), floral characters (pedicel length, flower colour), and numbers of fruit per stem. The new species was also reported as differing from P. cornifolium by a single substitution within the nrITS cistron, with that data obtained from a paper that did not provide a phylogenetic interpretation of this result, nor specify whether the cultivated plants used were derived from seed obtained from multiple individuals or from cutting grown plants from a limited wild-sourced selection. In this paper the same morphological characters used to separate P. roimata are examined using a much wider sampling of P. cornifolium, and the specimens available for P. roimata. There are very slight differences in leaf width and length, petiole length, and pedicel length in Poor Knights Islands P. roimata specimens seen also in some collections from other northern Aotearoa / New Zealand offshore islands and some mainland stations. Flower colour is not a useful character as this is variable in P. roimata and P. cornifolium, as it is also in many other Aotearoa / New Zealand Pittosporum. On the basis of our morphological assessment we conclude that to maintain the segregation of P. roimata from P. cornifolium at the species rank is impractical, as there is a grading of characters between both species. As plants corresponding to P. roimata occur throughout the range of P. cornifolium, already a variable species, we suggest that, in line with other treatments of Aotearoa / New Zealand Pittosporum, it is better to reduce P. roimata into synonymy of P. cornifolium.