Hibiscus calcareus McLay & Albr. 2023, sp. nov.
Creators: name: McLay, Todd G. B.
name: Barker, Robyn M.
name: Albrecht, David E.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malvales
Malvaceae
Hibiscus
Hibiscus calcareus

description: Hibiscus calcareus McLay & Albr., sp. nov.
Type: South Australia, Curnamona Station, W side of the Yunta–Arkaroola Road, ~ 590 m due W of Curnamona Homestead, 2 Mar. 2021, D.E. Albrecht 16345 (holo: CANB 914032! [Supplementary Fig. S4]; iso: AD!, NSW!).
[Hibiscus krichauffianus auct. non F.Muell.: F. J. H. von Mueller, Rep. pl. Babbage’s Exped. 7 (1859), p.p. [only as to some Goodwin specimens from Darling River labelled ‘B’ on MEL 0068091 A (Supplementary Fig. S2)]; G.Bentham, Fl. austral. 1: 216 (1863), p.p. [only as to Warburton specimen from Spencer’s Gulf]; F. J. H. von Mueller, Fragm. 9(78): 129 (1875), p.p. [as to Giles specimen from N of Fowler’s Bay (MEL 2223365 A)], as H. krichauffii; J. M.Black, Fl. S. Australia 3: 381 (1926), p.p.; J. M.Black, Fl. S. Australia 2nd edn, 3: 566 (1952), p.p.; Hj.Eichler, Suppl. Black’s Fl. S. Australia 223 (1965), p.p.; Western Australian Herbarium (1998), Florabase, Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/ browse/profile/4932c, p.p. [only as to collections from south-eastern Western Australia]; PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. https:// plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl= sp&name= Hibiscus ~krichauffianus, p.p. [only as to specimens from the Broken Hill–Wilcannia area].
Description
Low, spreading, many-branched, dome-shaped or rounded subshrub to 0.5 m tall but often less than 0.4 m tall. Branchlets very densely covered with sessile to shortly stalked stellate hairs 0.25–0.9 mm in diameter, indumentum white to silvery white. Stipules persistent or abscising with age, filiform–subulate, linear or very narrowly triangular, 2–6 mm long, 0.2–0.5 mm wide. Mature leaves simple and unlobed, petiolate; petiole 2–10 mm long, densely to very densely covered with sessile or shortly stalked stellate hairs; lamina narrowly to broadly ovate (the lowermost leaves tend to be broader), elliptic–ovate or oblong–ovate, mostly strongly concave to folded or conduplicate (distal leaves particularly strongly V-shaped in cross-section), 6–28 mm long, 4–16 mm wide; base broadly cuneate or truncate; margins serrate, dentate or crenate, undulate, the sinus between teeth to halfway to midvein, one or more proximal teeth sometimes larger than the other teeth; apex obtuse or broadly acute; adaxial surface grey to whitish-silver, abaxial surface similar or occasionally paler; midvein and primary veins equally covered by hairs on both surfaces, the lateral veins weakly or moderately raised and obscured by hairs; stellate hairs on adaxial surface moderate to very dense, occasionally sparse in oldest leaves, 0.4–0.6 mm in diameter, sessile to shortly stalked, multiradiate with 10–20 rays; stellate hairs on abaxial surface dense to very dense, 0.35–0.7 mm in diameter, sessile to shortly stalked, multiradiate with 8–25 rays. Flowers solitary in leaf axils; combined peduncle and pedicel 3–25 mm long, usually elongating in fruit, abscission line not always distinct, usually in distal half, 2–17(–24) mm from the base, indumentum as for young stems and petioles, broadening and flattening distally, often bent or recurved in fruit. Epicalyx lobes 7–8, narrowly linear or subulate and rarely linear–oblanceolate, 4–14 mm long, to ~ 1 mm wide, one-half to three-quarters the length of the calyx at anthesis, fused basally for 1–3.5 mm, becoming recurved in fruit, with sparse to dense stellate hairs abaxially. Calyx 10–19 mm long at anthesis; lobes narrowly triangular to triangular, 5–12 mm long at anthesis, abaxial indumentum of moderate to very dense stellate hairs, adaxial indumentum of dense appressed or ascending 1- or 2-armed hairs intermixed with stellate hairs particularly distally. Petals 20–44 mm long, adnate to staminal column at base but otherwise free, pale pink to pale lilac–purple, sometimes almost white, pigment often more intense after flowers senesced, lacking basal spot, glabrous adaxially, with sparse to dense stellate hairs abaxially towards the apex and near the margin on one side. Staminal column 12–18 mm long, apex irregularly 5-lobed, with the stamens distributed singly along the distal 6.5–8 mm of the column; staminal filaments 1.5–3 mm long; anthers yellow. Style 5-branched, with branches 2–3 mm long, exserted 3–4 mm beyond the apex of the staminal column. Stigmas capitate, 0.4–0.7 mm wide, distinctly hairy, hairs 0.2–0.3 mm long. Ovary 5-locular, with hairs 0.4–1 mm long. Capsule ovoid to globose, 8–12 mm long, usually very shortly beaked, beak to ~ 1 mm long, densely covered with simple shiny appressed hairs, the apical hairs erect, 0.4–1.3 mm long and extending beyond apex of capsule. Seeds angular–reniform with the two abaxial sides flat to convex, 2.5–3 mm long and almost forming a right angle at the junction, dark brown, with a short patchy indumentum of appressed white to yellow–brown simple hairs with a minute persistent tubercle base; funicular remnants brown, membranous and wing-like, on either side of the hilum. (Fig. 2 c, 3 c, 4 c.)
Distribution and habitat
Hibiscus calcareus occurs from eastern Western Australia near the Great Victoria Desert, through South Australia and into western New South Wales near Barringun, between latitudes 29 and 35̊S (Fig. 1, blue triangles). The distribution of this species is likely strongly associated with landform and soil type, as many collection records report plants growing on plains with lime-rich soils (e.g. Milthorpe & Cunningham 1928, NSW 624403; Symon NYPE-1300, AD 98805401; Milthorpe 680, NSW 684440, as ‘solonised brown soil’; and Bates 14221, AD 98821007). The substrate at the sites supporting this species typically has a low rate of percolation of water. Some sites have surface stones or even a thin surface veneer of sandy loam. The record Constable s.n. (NSW 684435) from ‘high rocky ground’ is anomalous and requires further investigation. The limited notes on the specimens seen suggest this species grows in grasslands, open woodlands and shrublands, featuring chenopodiaceous shrubs and Acacia (including A. papyrocarpa Benth.). At the type locality the species occurs in run-on areas on a calcareous plain. Very sparse shrubs of Acacia victoriae Benth., Eremophila duttonii F.Muell. and Atalaya hemiglauca occur at this site. The lower shrub stratum is dominated by Maireana astrotricha (L.A.S.Johnson) Paul G.Wilson, with associated species including Cullen cinereum (Lindl.) J.W.Grimes, Erodiophyllum elderi F.Muell., Sida fibulifera Lindl., Minuria leptophylla DC., Rhodanthe floribunda (A.Cunn. ex DC.) Paul G.Wilson, Enneapogon cylindricus N.T.Burb., Sclerolaena patenticuspis (R.H.Anderson) Ulbr. and Swainsona viridis J.M.Black.
Phenology
Specimens with flowers (17 in total) were collected from January to October, with 11 flowering collections made between March and May.
Conservation status
The status of this species would be considered Data Deficient (International Union for Conservation of Nature 2012). Owing to the small number of specimens seen, the relatively restrictive habitat type in calcareous soils and that attempts to relocate the species at some existing collection sites in NSW were unsuccessful, a Vulnerable or Endangered status could be required.
Etymology
The epithet calcareus is a Latin adjective meaning 'of or pertaining to lime' and refers to the species' association with soils overlying limestone or calcrete.
Affinities
Hibiscus calcareus is similar to H. krichauffianus and these two are likely closely related or sister taxa. Hibiscus calcareus is distinguished from H. krichauffianus in habit (low, spreading dome-shaped or rounded, cf. upright, erect or ascending stems in H. krichauffianus) and habitat (occurring on plains with slow-draining lime-rich soils, cf. deep sands in H. krichauffianus), lamina size (although this character can overlap, H. calcareus usually has smaller leaves 6–28 mm long and 4–16 mm wide, cf. 10–55 mm long and 5–35 mm wide in H. krichauffianus), lamina shape in transverse section (mostly strongly concave to folded or conduplicate in H. calcareus, cf. flat to weakly concave or weakly folded in H. krichauffianus), leaf margins (undulate, serrate to dentate or crenate, often deeply so with the sinus between dentations extending up to half-way to the midvein, cf. crenate or dentate in H. krichauffianus), with pedicel abscission point usually in the upper half of the flowering stalk, 2–17 mm from the base (cf. only 1–2 mm from the base in H. krichauffianus) and seeds that are angular in profile (cf. rounded in profile in H. krichauffianus), with an indumentum of shorter, more rigid appressed hairs (cf. longer wispy hairs that are not regularly appressed in H. krichauffianus). Sometimes depauperate plants of H. krichauffianus growing in marginal habitats can approach H. calcareus in appearance, typically by being smaller in stature and having smaller leaves. Examples of these specimens of H. krichauffianus include Mills & Cox 238 (NSW 624404), Percival 73 (CANB 866287), Clarke 2999 (MEL 2073274A) and Lawrie 1646 (NSW 624396). However, these can be distinguished from H. calcareus by leaf dentation and seed characters. These differences are stable under common growth conditions and not strictly controlled by growth on limestone or calcrete (Supplementary Fig. S5).
Notes
The available specimens limited our certainty about some characters, especially flower measurements.
Selected specimens examined
(30 specimens seen)
WESTERN AUSTRALIA. 78 km S by track of Ilkurlka roadhouse, Great Victoria Desert, Laverton, Oct. 2010, R.Davis & J. Jackson 11710 (PERTH). SOUTH AUSTRALIA. 10 km east-south-east of Benagarie, 10 Apr. 1976, L. D.Williams 7927 (AD); Erudina Station, 25 Apr. 1988, R. Bates 14221 (AD); Nillinghoo Mine, N.E of Koonamore Station, 10 Oct. 1987, A.G. Spooner 10905 (AD); Sandy flat S of Frome Downs, 15 May 1980, K. Paijmans 3483 (CANB); Black Oak Plains, Quandong Homestead (Quandong Homestead is ~ 140 km east of Peterborough), 31 Jan. 1968, S. Barker 180 (AD); Towards Spencers Gulf, s. dat., P.E. Warburton s.n. (MEL 2223362); Vulcan Paddock, Roopena Station, via Whyalla, s. dat., R.T. Lange s.n. (AD 99616857); Whyalla, 14 Apr. 1983, P. Hudson s.n. (AD); ~ 13 km WSW of Tarcoola township, 23 Apr. 1992, P. Hornsby s.n. (AD); Mt Finke Site, 2.0 km east Mt Finke trig, Quadrat 2, 8 Oct. 1987, D.E. Symon for N.P.W.S 1300 (AD); Ooldea near siding sign, 22 May 2014, D.E.Murfet 7738 & D.J. Duval (AD); 29 km west north-west of Oak Valley, Great Victoria Desert, (TERN site code: SAAGVD0002) 9 Mar. 2014, E. Leitch SAA003896 (CANB). NEW SOUTH WALES. 1 mile [~ 1.6 km] north Wilcannia, 30 Mar. 1974, P.L.Milthorpe & G.M. Cunningham 1928 (NSW); Byrnedale Station via Broken Hill, 1 Apr. 1949, R.L. Caskey (NSW); Broken Hill, 1 March 1920, A. Morris 162 (NSW); Broken Hill, 29 Apr. 1956, F. Apperkuch McB. No. 6492 (NSW); Silverton, 25 Nov. 1947, E.J. Constable s.n. (NSW).
description: Published as part of McLay, Todd G. B., Barker, Robyn M. & Albrecht, David E., 2023, Morphological and environmental variation within Hibiscus krichauffianus (Malvaceae), and the recognition of two new species, H. verecundus and H. calcareus, pp. 457-477 in Australian Systematic Botany 36 (6) on pages 473-475, DOI: 10.1071/SB23003, http://zenodo.org/record/13835582