Solenogyne christensenii, comb. nov. (Asteraceae: Astereae), a new combination for a New Zealand species

The new combination Solenogyne christensenii (Petrie) de Lange, Jian Wang ter & Barkla comb. nov. is validated for a New Zealand species originally published as Abrotanella christensenii Petrie. The species is described, illustrated and differentiated from similar and related taxa. The species is seriously threatened, being known with certainty only from the South Island of New Zealand where there is one extant population in Otago, though the species was also known historically from the type locality, Hanmer Plain, North Canterbury.


Introduction
The genus of Solenogyne Cass. was established by Cassini (1828) for those plants that resemble Lagenophora Cass.; the latter is now recognized as a genus containing ca. 25 species occurring mainly in Australasia, South America, and southern and south-eastern Asia (Wang, Bean, 2019). Cassini (1816) initially published this as "Lagenifera", the spelling of which he later corrected to Lagenophora (Cassini, 1818), and that latter spelling was conserved (Art. 14.11 of the ICN: Turland et al., 2018) following the nomenclatural proposal by Nicolson (1996). Subsequently the two genera (Solenogyne and Lagenophora) were united by Hooker (1860) and Bentham (1867), and this was followed by Maiden and Betche (1916). It was Davis (1950) who revised and reinstated Solenogyne as a distinct genus. Her research was followed by Cabrera (1966) who further distinguished the two genera by differences in their achenes, e.g., those of Solenogyne are without a beak and glands.
As currently circumscribed, Solenogyne includes four species (Fig. 1, 2): three in Australia and one in Japan. At the time when the genus was erected, there was only one species recognised, S. bellioides Cass. described from near Port Jackson (modern Sydney area), New South Wales, Australia (Cassini, 1828). Exactly a century later, Koidzumi (1928) published S. mikadoi Koidz., the second species of the genus from Amamiohsima [Amami Ōshima, Amami Islands of the Satsunan islands group, Kagoshima Prefecture], Japan. Solenogyne gunnii (Hook.f.) Cabrera from Tasmania and S. dominii L.G.Adams from Australian Capital Territory, as the third and fourth members of the genus, were published by Cabrera (1966) and Adams (1979), respectively. Solenogyne mikadoi is now often treated as Lagenophora mikadoi (Koidz.) Koidz. ex H.Koyama (cf. Plants of the World Online http://powo.science.kew. org/taxon/249376-1), although this is not confirmed by phylogenetic studies (Nakamura et al., 2012;Sancho et al., 2015), or followed in Australasia (Schönberger et al., 2019).
New Zealand has three Solenogyne species, all treated as naturalised: S. mikadoi, S. dominii, and S. gunnii (Drury, 1974;Webb et al., 1988). Of these, S. mikadoi is extremely uncommon, while S. dominii is locally common, particularly around Christchurch and Banks Peninsula. Solenogyne gunnii is the most widespread species, often occurring as an urban weed in lawns and street side verges in the main centres of New Zealand.
An enigmatic species of Abrotanella Cass., known only from the type collected by Charles E. Christensen from the Hanmer Plain, Amuri District, North Canterbury, was described by Petrie (1915) as A. christensenii Petrie. However, following critical examination of the type, this species was considered by Swenson (1993) to be conspecific with Solenogyne gunnii. There the matter of Abrotanella christensenii seemed to rest until an Asteraceous plant was discovered in a herbfield under kahikatoa (Leptospermum scoparium J.R.Forst. & G.Forst. s. l.) shrubland, near the outlet of Lake Wanaka, on the side of the Clutha River, Otago, by John Barkla in the early 2000s. That plant morphologically matched the type of Abrotanella christensenii; it was tentatively assigned to Solenogyne gunnii by Peter de Lange though it differed from that species with respect to its smaller overall stature, leaf colour, size and shape, and by having fewer disc florets. Specimens from this population were included in a phylogenetic study of Lagenophora (Sancho et al., 2015) where they were found to be sister to Solenogyne gunnii, thus further highlighting the possibility that these plants represented a fifth species of Solenogyne, the one endemic to New Zealand. Following further examination of herbarium material and live plants, it is evident that Abrotanella christensenii, though allied to Solenogyne gunnii as Swenson (1993) thought, is a distinct species in its own right, and so a new nomenclatural combination in Solenogyne is made here.

Materials and methods
This article is based on the study of live plants cultivated in Dunedin, South Island, New Zealand, by John Barkla and the morphological examination of Solenogyne material at AK, BRI, CHR, MEL and WELT; herbarium acronyms follow Thiers (2020-continuously updated). All measurements are based on live plants, as well as dried material, except the dimensions of florets, in which material was reconstituted with boiling water.
Note: Although Petrie (1915) did not specify a type, Cheeseman (1925) makes clear that there were only the two specimens held by Petrie, stating (p. 1005) "Only 2 specimens, which have been kindly lent [our emphasis] to me for examination by Petrie have been found", both specimens, are the same Christensen gathering that were forwarded by Leonard Cockayne (as became his practise when dealing with taxonomic matters: see Cockayne (1926), Thomson (1990), and de Lange (2019) for an account of Cockayne's stance on taxonomy) to Petrie. These are now mounted on the same sheet, WELT SP02098 (Fig. 3) held in the Petrie Herbarium, and labelled in Petrie's hand "Type Specm.". Therefore, Art. 9.1 of the ICN (Turland et al., 2018) applies, e.g., "A holotype of a name of a species or infraspecific taxon is the one specimen or illustration [bold type our emphasis here and thereafter] (but see Art. 40.4) either (a) indicated by the author(s) as the nomenclatural type or (b) used by the author(s) when no type was indicated. As long as the holotype is extant, it fixes the application of the name concerned (but see Art. 9.15)". With respect to the number of specimens, Art. 8.2 applies ("for the purpose of typification a specimen……may consist of a single organism, parts of one or several organisms, or of multiple small organisms") because the two specimens mounted on WELT SP02098 are part of the same gathering used by the naming author to describe Abrotanella christensenii. Nevertheless, Swenson (1993, p. 3) was under the impression that the two specimens referred to by Cheeseman (1925) were different collections held by different herbaria, perhaps misunderstanding Cheeseman's statement that Petrie "lent" him the specimens to study, stating "…that no more collections than the two cited by Cheeseman (1925) exist, i.e. the type specimens: C. Christensen, March 1912 (lectotype WELT). However, I have only been able to locate one of these sheets, the one deposited in Wellington (WELT), the second was presumably deposited in Auckland (AK) by Dr Petrie, but no type is held according to the herbarium". Thus he cautiously referred to WELT SP02098 as "Lectotype" presumably following the type statement of Allan (1961, p. 695) ("Type: W[ELT], C.E. Christensen") in the belief that two specimens had existed, and that one of those was now missing. However, Cheeseman on examining Petrie's two specimens (in fact, two plants) returned them to Petrie, and they now reside on the same herbarium sheet in his herbarium. Therefore, the type statements by Allan (1961) and Swenson (1993) can be taken as lectotype designations, but only if two or more syntypes or other original elements exist (or definitely existed). Since there are good reasons to believe that Petrie used only the two plants now mounted on the same sheet in WELT, that specimen in fact constitutes the holotype for his species name.  (Fig. 3, 4): Small perennial rhizomatous tufted herb up to 30 mm tall and 50 mm across; roots and rhizomes fibrous; stem very short (leaves in basal rosette); leaves and scapes firmly attached to stem and/ or rootstock. Leaves 15-25, oblanceolate, obdeltoid to cuneate, 10-20(-25) × 5-8 mm (10-5× longer than wide), with a winged petiole-like base 8-10 mm long; leaf apex tridentate; leaf margins serrated (rarely repandsinuate), usually with 4-6 teeth either side, each lobe 0.5-1.0 mm long; adaxial leaf surface glossy, initially green, maturing bronze-green or brown mottled, or maroon-brown; adaxial surface pilose, hairs patent eglandular, 0.3-1.8 mm long, 3-8 per mm 2 ; abaxial leaf surface pale glossy green, ± glabrescent; hairs present on young leaves, unevenly shedding with leaf maturation, eglandular, pubescent, ± appressed, 0.4-0.8 mm long, 0-2 per mm 2 , hairs; both leaf surfaces papillate, papillae c. 0.01 mm long, more or less evenly distributed; leaf margins pilose, hairs eglandular patent 3-4 per mm 2 , 0.2-1.0 mm long; lateral veins slightly raised and usually visible adaxially, obscure abaxially. Scapes terete and smooth on fresh specimens, channelled on dry ones, 4-8 per tuft, each 5-20 mm long at anthesis, 10-30 mm long at fruiting stage, 1.5-2.5 mm diameter throughout; scape bracts 0, or occasionally furnished with 1, ovate to orbicular, chartaceous c.1.5 × 0.4 mm bract; scape indumentum including eglandular hairs 0.3-1.0 mm long, patent, spreading or mixed weakly appressed / retrorse; 1-6 hairs per mm 2 ; and papillae to c.0.01 mm long, scattered throughout the scape. Capitula 1.8-2.2 mm long, 2.8-3.0 mm diameter; involucral bracts 18-22 in 2 rows, glabrous or occasionally papillate along midrib on outer surface, ovate to broadly oblong, apex obtuse to rounded, margins pink, ciliate in upper distal ½-¾; outer bracts 1.2-1.6 × 1.0-1.6 mm, inner bracts 1.1-1.2 × 0.9-1.0 mm. Receptacle flat to slightly convex, 0.8-1.2 mm diameter. Ray florets tubular, creamy to pale pink, 18-20 in 2-3 rows; tube 0.4-0.7 mm long, 0.1-0.12 mm wide; style 0.5-0.8; stigma 2-branched c.0.02 mm long. Disc florets 0-3; corolla pale yellow, tubular, c.1 mm long, outer surface glabrous; corolla lobes 5, deltate, c.0.1 × 0.1 mm; stamens 5, to c.0.4 mm long; style c.0.6 mm long; sterile ovary c.0.3 mm long. Achenes glabrous, more or less flattened, narrowly obovoid, straight or slightly curved, 0.9-1.1 mm long by 0.3-0.5 mm wide excluding beak, uniformly yellow green, darkening to brown at maturity; achene edges smooth; achene beak Etymology: Petrie (1915) named this species after Charles E. Christensen  who was the first person to collect this species, as Abrotanella christensenii, during his botanical exploration of the vegetation of Hanmer Plain, Amuri District, North Canterbury, New Zealand (Godley, 1994).

Distribution and habitat: Endemic to New
Zealand where it is restricted to montane shrubland at approximately 280 m above sea level in the upper Clutha Valley of Otago (Fig. 1). At its only extant site (Fig. 5) it grows in tiny patches within a 25m 2 herbfield on silty riverbank under dappled shade provided by 2-4 m tall kahikatoa. In the past it has also been recorded from "bare spots in dry fescue [Festuca novae-zelandiae (Hack.) Cockayne] tussock steppe" from the Hanmer Plains (Petrie, 1915). Phenology: In the wild both flowers and fruits were observed mid-April. In cultivation, plants have been observed beginning to flower in January, with fruits evident a month later, with fruiting extending at least through to May.

Conservation status:
Solenogyne christensenii is an extremely uncommon species only known with certainty from one small population comprising less than 100 plants. Under the New Zealand Threat Classification System (Townsend et al., 2008), its conservation status, as Abrotanella christensenii, is listed as Nationally