A cladistic analysis of Boronia Sm. and Boronella baill. (Rutaceae)

Abstract

Boronia and Boronella form a monophyletic group within the tribe Boronieae of the Rutaceae. A cladogram for this group, constructed using 32 morphological characters, is presented. According to this hypothesis, Boronella is a monophyletic subgroup within Boronia, rendering the latter genus paraphyletic, and therefore we recommend that Boronella be included within Boronia. Two competing hypotheses of cytoevolution in Boronia are evaluated by superimposing them onto the cladogram. Smith-White's model requires fewer postulated polyploid and aneuploid changes in numbers of chromosome than James' model and is therefore preferred. The sister group of the New Caledonian species (Boronella plus Boronia koniambiensis) is restricted to disjunct south-eastem and south-westem areas in Australia. Under a vicariance model of historical biogeography this indicates that New Caledonia separated from Australia before the east-west separation within Australia. Wilson has provided the most satisfactory infrageneric classification for Boronia when compared with the cladogram.