Leionema, (F.Muell.) Paul G.Wilson

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 : 133-134

Leionema

Leionema is monophyletic with robust support (Clade 10: 1.00 PP, 100% JK; Fig. 1 , 2 , S 1 , S 2 ; 27 of 28 species and all 8 subspecies represented). The only species not represented in this study is L. elatius (F.Muell.) Paul G.Wilson (NE NSW) . That species was recently revised by Telford and Bruhl (2020), who determined that the two subspecies previously recognised (see Wilson 1998 b, 2013 a) each warrant specific rank and that the typical form is a narrow endemic, in contrast to how it had been treated previously. Most material previously assigned to L. elatius subsp. elatius is now included in the more widespread L. beckleri (F.Muell.) I.Telford & J.J.Bruhl. Wilson (1970 , 1998 b) noted that the relationship of Leionema to other genera in tribe Boronieae is not clear; however he did indicate that it has no close affinity to Phebalium sens. strict., Rhadinothamnus or Nematolepis , a statement supported by this study. Leionema , like Diplolaena , Correa and Myrtopsis , is indisputably part of the Eriostemon Group but has no clearly identifiable close relatives.

Relationships within Leionema have some strong to robust support in all analyses. Leionema ellipticum (NE Qld) is sister to a robust clade (1.00 PP, 100% JK) containing the remaining species, confirming the results of Mole et al. (2004). Within this later clade, L. nudum ( New Zealand) is sister to strongly supported clade (1.00 PP, 99% JK) containing all remaining taxa ( SE Aust., including Tas.). Within the south-eastern Australian clade, there are a number of species groups. These include the following: (1) a South Australian clade (1.00 PP, 100% JK) containing all three species found in that state, namely, L. equestre (D.A.Cooke) Paul G.Wilson , L. hillebrandii (J.H.Willis) Paul G.Wilson and L. microphyllum (F.Muell.) Paul G.Wilson (also in W Vic.); (2) a Tasmanian clade (1.00 PP, 87% JK) containing both Tasmanian endemic species L. montanum (Hook.) Paul G.Wilson and L. oldfieldii (F.Muell.) Paul G.Wilson , a relationship noted by Wilson (1970), which was not retrieved in the nuclear analyses; (3) a clade containing L. ceratogynum N.G.Walsh , L. diosmeum (A.Juss.) Paul G.Wilson , L. lachnaeoides (A.Cunn.) Paul G.Wilson , L. phylicifolium (F.Muell.) Paul G.Wilson , and L. coxii (F.Muell.) Paul G.Wilson (1.00 PP, 82% JK; L. coxii is not part of this clade in the nuclear analyses); and (4) all four subspecies of L. bilobum (Lindl.) Paul G.Wilson (3 Vic., 1 Tas.) (1.00 PP, 100% JK). The remaining species group with these clades and other species with mixed support. Most species of Leionema were monophyletic where multiply sampled, although there is some paraphyly, which indicates that further investigation is needed of the circumscription of L. lamprophyllum (F.Muell.) Paul G.Wilson and the relationships of its subspecies with both L. beckleri and L. praetermissum P.R.Alvarez & Duretto.

Leionema ellipticum was first collected in 1991 from a mountain top in the Humid Wet Tropics of north-eastern Queensland, an area rich in endemics and taxa with significant phylogenetic isolation and varied geographic connectivity. Wilson (1998 b), when describing L. ellipticum , noted that it differed from all other species in the genus by having minutely apiculate anthers that are bluntly mucronulate (v. retuse) and a grooved disc or gynophore divided into 10 parts (v. entire), and suggested that it may not be correctly placed in the genus and may warrant a genus of its own. Mole et al. (2004) considered that L. ellipticum could be placed in either a monotypic genus or a new section of Leionema . Wilson (1998 b) and Mole et al. (2004) are correct; the isolated position of L. ellipticum is confirmed and so warrants taxonomic recognition, either as a monotypic genus or a monotypic infrageneric taxon within Leionema . Morphologically the species is similar to the remainder of the genus and this relationship is supported by the predominance of the coumarin osthol in both L. ellipticum and many other species of Leionema ( Halstead et al. 2005) . To reflect the phylogenetic signal, a new monotypic section is formally described here to accommodate the species (see Taxonomy below).

Wilson (1970) indicated that although Leionema nudum ( New Zealand) showed no close affinity to other species in Leionema (E Aust.) , it clearly belonged in the genus. No obvious morphological apomorphies can be discerned for the remaining species in the south-eastern Australian clade to distinguish them from L. nudum . Within the south-eastern Australian clade, there are some species groups (see above) but most of the other species do not fall into groups, and the groups themselves are not always easy to define morphologically. In NSW, there are several species that have pendent flowers ( L. carruthersii (F.Muell.) Paul G.Wilson , L. ralstonii (F.Muell.) Paul G.Wilson , L. sympetalum (Paul G.Wilson) Paul G.Wilson , L. viridiflorum (Paul G.Wilson) Paul G.Wilson ), a character shared with some species in other genera (e.g. Correa and Diplolaena ), but only L. ralstonii and L. viridiflorum group together (see also discussion below under Pollination). No formal taxonomic groups will be recognised within the typical section of Leionema .

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)