Nematolepis, Turcz.

Duretto, Marco F., Heslewood, Margaret M. & Bayly, Michael J., 2023, Generic and infrageneric limits of Phebalium and its allies (Rutaceae: Zanthoxyloideae), Australian Systematic Botany 36 (2), pp. 107-142 : 134

Nematolepis

Nematolepis is monophyletic with robust support (Clade 8: 1.00 PP, 100% JK; Fig. 1 , 2 , S 1 , S 2 ; see also Mole et al. 2004; all seven species and both subspecies of N. squamea (Labill.) Paul G.Wilson sampled). The genus is most closely related to the Chorilaena + Rhadinothamns clade (= Chorilaena sens . lat.; see above). In all analyses, south-eastern Australian species formed a robust clade (Clade 8 E: 1.00 PP, 100% JK) sister to the sole south-western Australian species, N. phebalioides . Nematolepis phebalioides differs from all other species in having pendent flowers with a tubular fused corolla that is red with green or yellow tips (see discussion on Pollination below). The other species have cymose non-pendent inflorescences and flowers with spreading, unfused, white or yellow petals. The south-eastern clade is strongly supported and both clades can be defined on morphological characters, and so they warrant taxonomic recognition.

Wilson (1970) considered that Phebalium (which at the time of his publication included the south-eastern Australian species of Nematolepis ) was diverse morphologically and its sections appeared to be more closely related to other genera than they were to each other. He retained Phebalium in the broad sense because he considered that there was gradation between the taxa. Wilson (1970) did note that P. section Eriostemoides , which included all south-eastern Australia species now placed in Nematolepis , shared with N. phebalioides the following characters: two subfloral bracteoles, free and imbricate sepals, glabrous petals, and slightly retuse anthers and seed characteristics. Wilson (1998 b) later transferred the species of P. section Eriostemoides to Nematolepis , although he did not make a combination for the section under that genus. The type species of P. section Eriostemoides is N. squamea and, so, a name is available for the south-eastern clade. The rank of section for the two clades is appropriate and a new combination in Nematolepis for P. section Eriostemoides is made below (see Taxonomy). There is weak or no support for relationships within the south-eastern clade. The only species in the genus with multiple accessions, namely N. squamea , was polyphyletic, as were both of its subspecies. Further work is required to determine species limits and relationships of the species in this section.

An apparent absence of speciation in the western lineage, which is monotypic and sister to the eastern clade, is not due to a younger age and there is no evidence that this lineage resulted from a later dispersal. With Rutaceae being poorly represented in the fossil record, we cannot speculate about the possible role that extinction of species might have had on such depauperate lineages. Instead, this pattern could reflect factors such as the greater prevalence of bird pollination ( Keighery 1980; Phillips et al. 2010) and a simpler landscape topography maintaining genetic connectivity over broader areas in the west ( Phillips et al. 2010).

Figures

Fig. 1. Simplified version of the Bayesian 50% majority-rule consensus tree of combined molecular data, with thick lines showing supported clades (≥0.95 PP). Genera have been collapsed on the basis of sampling density, to provide a snapshot of the overall relationships.

Fig. 2. (Caption on next page)