Asterolasia, F.Muell.

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 : 130-131

Asterolasia

Of the 19 species and 4 subspecies recognised in Asterolasia , 17 species and 3 subspecies were included in this study. Asterolasia exasperata P.R.Alvarez & Duretto (NSW) and A. sola Duretto & P.R.Alvarez (Qld) , which were recently segregated from A. correifolia (A.Juss.) Benth. (NSW) ( Alvarez and Duretto 2019 a), were not included in the study, and neither was A. asteriscophora subsp. albiflora B.J.Mole (Victoria, Vic.). Asterolasia is monophyletic (Clade 9: Fig. 1 , 2 ) and its species form two robustly supported subclades, namely, one with all five south-western Australian species (Clade 9 W: Fig. 2 ), and the other with all the south-eastern Australian species (Clade 9 E: Fig. 2 ). In the south-eastern Australian clade, A. muricata J.M.Black (SA) is sister to the remaining species, which form a robustly supported group (1.00 PP, 100% JK), and then in a stepwise fashion A. phebalioides F.Muell. (SA, W Vic.) is sister to an unsupported clade (0.82 PP, 82% JK), and then A. trymalioides F.Muell. (alpine areas, SE Aust.) to a robustly supported clade containing species mainly from non-alpine areas in New South Wales ( A. asteriscophora (F.Muell.) Druce is also in eastern Vic.) (1.00 PP, 100% JK), which has little internal support. Morphological evidence indicates that A. exasperata and A. sola are closely related to A. correifolia of this last clade.

Within the south-western Australian clade, there is weak to robust support for the internal structure, with A. drummondii Paul G.Wilson (the most northerly species in this clade) sister to a moderately supported clade (1.00 PP, 82% JK) containing the remainder, and then, going up the tree, A. hyalina (Paul G.Wilson) Wege , A. pallida Benth. , and then A. squamuligera (Hook.) Benth. sister to A. grandiflora (Hook.) Benth. Results are consistent with both propositions put forward by Wege (2017), namely that A. nivea (Paul G.Wilson) Paul G.Wilson is a synonym of A. grandiflora , and that the subspecies of A. pallida , as outlined by Wilson (1998 c, 2013 e), should each be recognised at specific rank. The two samples of A. grandiflora in these analyses represented the forms previously recognised as the two separate species, namely A. grandiflora sens . strict. and A. nivea ; the results using molecular data confirmed that at least they are closely related, with the length of the branches like that seen within other species. Asterolasia pallida , if circumscribed in the broad sense with two subspecies, i.e. including samples identified here as A. hyalina , would be paraphyletic.

The two clades of Asterolasia are each robustly supported and clearly distinct on molecular grounds and are here considered worthy of taxonomic recognition. The type species of Asterolasia is A. trymalioides of the south-eastern Australian clade. Generic and subgeneric synonyms of Asterolasia are Actinostigma Turcz. (type: Actinostigma lanceolatum Turcz. = Asterolasia correifolia ), Pleurandropsis Baill. (type: P. phebalioides (F.Muell.) Baill. = A. phebalioides ), Urocarpus J.Drumm. ex Harv. (type: U. phebalioides J.Drumm. ex Harv. = A. drummondii ), Asterolasia section Urocarpus (Drumm. ex Harv.) Benth. , Asterolasia sect. Pleurandropsis (Baill.) Kuntze , Phebalium a. Correoides Endl. (containing A. correifolia and A. hexapetala (A.Juss.) Druce ), and Phebalium section Correoides (Endl.) Pfeiff. As with Asterolasia , the type species of all these taxa are in the south-eastern Australian clade (see Wilson 1971, 1987, 1998 c, 2013 e) except that for Urocarpus , which is from south-western Australia. The names Asterolasia and Urocarpus were published at nearly the same time and there has been some conflict over which genus has priority (see Wilson 1971, 1980, 1987). Until 1971, Asterolasia was considered to be the earliest published name. When revising the genus, Wilson (1971) considered Urocarpus to have precedence, believing that it had been published several months earlier in 1855 than was Asterolasia . However, he considered that both genera could be segregated on the basis of carpel number, with Urocarpus sens . strict. having two or three carpels and all south-eastern Australian species, except A. muricata (SA) , having five carpels. Wilson (1971) transferred A. muricata and the south-western Australian species that did not already have validly published names in Urocarpus to that genus, leaving the remaining species in Asterolasia and noting that any further nomenclaturial changes must await further taxonomic study. The result was that from 1971, both names were in use. Wilson (1980), when describing U. niveus Paul G.Wilson from south-western Australia, noted that because this species had three or four carpels, there was a gradation of carpel number between Urocarpus and Asterolasia . He concluded the two genera could not be maintained as distinct but did not transfer the south-eastern Australian species of Asterolasia to Urocarpus and so the two generic names remained in use. The issue was later simplified when the publication date for Asterolasia was determined to be in 1854 and not 1855 ( Aston 1984; Wilson 1987), thus giving Asterolasia precedence over Urocarpus . Wilson (1987) recognised a broad concept for Asterolasia to cover both south-western and south-eastern Australian species and ensured that all accepted species had validly published names in Asterolasia .

South-western Australian species have one to four carpels, as opposed to species found in south-eastern Australia, which have five carpels, except A. muricata , which has two carpels and is the sister species to the remainder of the south-eastern clade. The name Asterolasia section Urocarpus is available for the south-western clade. There do not seem to be clear morphological apomorphies for either of these geographic clades, even though there is strong molecular support for them. Removing A. muricata from A. section Asterolasia would resolve some issues but would require creation of a third monotypic section without clear apomorphies, or, if placed in A. section Urocarpus , a paraphyletic section. This is a situation similar to that found in Boronia section Boronia where there were clearly demarcated groups on the basis of molecular data, one in south-eastern Australia and another in south-western Australia, but without identifiable morphological apomorphies ( Duretto et al. 2023).

The south-eastern Australian species of Asterolasia have yellow or white petals, whereas those in the south-west have flowers with white or pink petals, except for A. squamuligera , which has yellow petals. The character used to distinguish Urocarpus from Asterolasia was having one to four carpels as opposed to five. All south-western species have the reduced number of carpels, as does A. muricata from South Australia, which is the sister species of a robust clade containing all other species from south-eastern Australia. The relationship between A. muricata and the remaining south-eastern species is robust and the branch length between it and the other species is not significantly long. Reduction in carpel number is unusual in Australasian Rutaceae (see also discussion under Phebalium and Microcybe ). It could be inferred from the results presented here that a reduction in carpel number is a plesiomorphic state for the genus and having five carpels is a reversion. Alternatively, an equally parsimonious hypothesis is that reduction in carpel number has evolved twice in the genus, i.e. on the branch leading to south-western Australian species and on that leading to A. muricata . Although a reduced carpel number may or may not be an apomorphy for the genus, it is potentially a good diagnostic character to define a section based on Urocarpus , except for a problem regarding the placement of A. muricata . To recognise only two clades (south-eastern and south-western, 9 E and 9 W in Fig. 2 ) would mean that neither clade can be defined morphologically. Formally recognising a third monotypic clade comprising A. muricata would enable a formal classification that would be practicable and acknowledge the isolated placement of A. muricata . These taxa being recognised at a sectional level is appropriate, given that the two clades partially defined by a reduced carpel number lack other clear-cut morphological features to separate them. Here we recognise the following three sections for Asterolasia : section Asterolasia ( SE Aust., 13 spp.; 5 carpels; yellow or white petals), section Urocarpus ( SW Aust., 5 spp.; 1–4 carpels, white, pink or yellow petals, if yellow then stellate hairs with the rays fused so that the hairs look like fimbriate scales and leaves flat), and section Muricatae Duretto & Heslewood ( SA, monotypic; 2 carpels, yellow petals with stellate hairs with unfused rays, leaves revolute), which is formally described below.

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)