Hibiscus verecundus McLay & Albr., 2023

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, Australian Systematic Botany 36 (6), pp. 457-477 : 471-473

Hibiscus verecundus McLay & Albr. , sp. nov.

Type: Queensland , Poison Valley Track , White Mountains National Park, 13 Apr. 2000, K. R. McDonald KRM463 (holo: BRI AQ 496863 ! [Supplementary Fig. S3 ]; iso: DNA D0156915!) .

[ Hibiscus krichauffianus auct . non F.Muell.: F.J.H. von Mueller, Fragm. 6(46): 169 (1868), as ‘ H. krichauffi ’; E.J.Thompson et al., White Mountains Scientific Study Report, Geogr. Monogr. Ser. 9: 106 (2003); F.A.Zich et al., Australian Tropical Rainforest Plants Ed. 7 (2018); G.P.Guymer, Malvaceae in G.K.Brown & P.D.Bostock, Census Queensland Fl. 2020 (2021), http://www.data.qld.gov.au/dataset/ census-of-the-queensland-flora-2020, accessed Aug. 2023].

Low, spreading, usually decumbent subshrub to 0.5 m tall. Branchlets very densely covered with sessile to shortly stalked stellate hairs 0.5–1 mm in diameter, indumentum yellowish-brown on younger branchlets, sometimes fading to white with age. Stipules persistent or abscising with age, filiform to filiform–subulate, 1.5–6 mm long, 0.1–0.17 mm wide. Mature leaves simple and unlobed, petiolate; petiole 5–15 mm long, densely to very densely covered with sessile or shortly stalked stellate hairs; lamina ovate to broadly ovate, rarely elliptic–ovate, flat to weakly concave or weakly folded, 9–52 mm long, 8–33 mm wide; base broadly cuneate, obtuse or truncate; margins serrate to dentate, rarely crenate; apex obtuse or occasionally acute; adaxial surface green to dark green, abaxial surface paler (except in young leaves); abaxial main and lateral veins raised and obvious or obscured by hairs; stellate hairs on adaxial surface moderate to dense, 0.4–0.8(–1) mm in diameter, sessile to shortly stalked, multiradiate with 5–18 rays; stellate hairs on abaxial surface moderate to very dense, 0.3–1 mm in diameter, sessile to shortly stalked, multiradiate with 7–22 rays. Flowers solitary in leaf axils; combined peduncle and pedicel 3–22 mm long, usually elongating in fruit, abscission line sometimes obvious, one-third to one-half the length from the base, indumentum as for young stems and petioles, pedicel broadening distally. Epicalyx lobes 5–7, narrowly linear or subulate, 6–10 mm long, to ~ 1 mm wide, one-half to three-quarters the length of the calyx at anthesis, free to base or fused basally for up to ~ 0.5 mm, straight, not recurved apically, with moderate to dense stellate hairs abaxially. Calyx 9–15 mm long at anthesis, enlarging to 20 mm long in fruit; lobes narrowly triangular to triangular, 4.5–7 mm long at anthesis, enlarging to 12 mm long in fruit, abaxial indumentum of dense to very dense stellate hairs, adaxial indumentum of appressed or ascending 1- or 2-armed hairs intermixed with stellate hairs particularly distally. Petals 15–28 mm long, adnate to staminal column at base but otherwise free, light pink or white, sometimes drying pale yellow, lacking basal spot, glabrous adaxially, with sparse to moderate stellate hairs abaxially toward the margin on one side. Staminal column ~ 15.5 mm long, apex irregularly 5-lobed, with the stamens distributed singly along the distal 4–7 mm of the column; staminal filaments 2.5–5 mm long; anthers yellow. Style 5-branched, with branches 2.5–4 mm long, exserted 4–6 mm beyond the apex of the staminal column. Stigmas capitate, ~ 0.5 mm wide, distinctly hairy, hairs ~ 0.25 mm long. Ovary 5-locular, with hairs 0.4–0.9 mm long. Capsule ovoid to ellipsoid, 6–10 mm long, usually very shortly beaked, densely covered with stout shiny simple appressed hairs, the apical hairs erect, 1–1.5 mm long and extending beyond apex of capsule. Seeds angular–reniform with the two abaxial sides flat to convex, 1.7–2.3 mm long and almost forming a right angle at the junction, dark brown, with a short patchy indumentum of simple appressed white to yellowish-brown hairs with a minute persistent tubercle base, 0.25–0.4 mm long; funicular remnants brown, membranous and wing-like, one centrally placed and one on either side of the hilum, the central one occasionally detaching. ( Fig. 2 b , 3 b , 4 b .)

Distribution and habitat

Hibiscus verecundus is endemic to eastern central Queensland. Scattered populations occur within an area bound by Emerald in the south, Mt Garnet in the north, Duaringa in the east and Muttaburra in the west. Most occurrences are within the Leichhardt, Kennedy South and Kennedy North botanical regions, with fewer records from adjoining parts of the Cook, Burke and Mitchell botanical regions ( Fig. 1 , orange circles).

The species occurs in shrublands, woodlands and forests featuring an overstorey of Acacia (especially A. shirleyi Maiden , and also A. rhodoxylon Maiden and A. catenulata C.T.White ), or Eucalyptus (e.g. E. persistens L.A.S.Johnson & K.D.Hill , E. melanophloia F.Muell. , E. thozetiana (F.Muell. ex Maiden) R.T.Baker , E. drepanophylla F.Muell. ex Benth. and E. similis, Maiden ) or Corymbia (e.g. C. citriodora (Hook.) K.D.Hill & L.A.S.Johnson , C. trachyphloia (F.Muell.) K.D.Hill & L.A.S.Johnson and C. clarksoniana (D.J.Carr & S.G.M.Carr) K.D.Hill & L.A.S.Johnson ). One specimen was collected in the remnants of semi-deciduous vine thicket. The species occurs over a range of topographical positions including on ridges, plains, hillslopes, rocky outcrops, escarpments and gullies, and is typically associated with shallow soils overlying sandstone, laterite or basalt.

Phenology

Flowering specimens have been collected in January, March, April, May, June and November. Flowering is likely dependent on rainfall that predominantly occurs in summer within the geographic range of Hibiscus verecundus , but a reasonable amount of rainfall can occur in any month in the region.

Conservation status

Following International Union for Conservation of Nature (2012) threat assessment definitions, Hibiscus verecundus has an approximate Extent of Occurrence (EOO) of 15 400 km 2 and occurs in several nature reserves (Epping Forest National Park, White Mountains National Park and Blackwood National Park). The species has a much smaller Area of Occupancy (AOO) of 180 km 2 based on ~25 collections and populations seen by the authors are generally small (<10 plants) (but due to the small stature of the species individual plants could easily be overlooked). The conservation status is possibly of Least Concern but could be Vulnerable. Until further surveying is undertaken to obtain a more accurate estimation of population number and size, and population decline, the species should be considered Data Deficient.

Etymology

The species epithet is the Latin adjective verecundus , meaning modest or shy ( Lewis and Short 1879), referring both to the fact that this entity was overlooked despite being very distinct from Hibiscus krichauffianus and to the difficulty in finding this species in the field.

Affinities

Specimens of Hibiscus verecundus have previously been included within H. krichauffianus , though whether the two species are particularly closely related is uncertain. Hibiscus verecundus is readily distinguished from H. krichauffianus by the branchlet indumentum colour (yellowish-brown, sometimes fading to white, cf. white or silvery sometimes fading to yellowish-white in H. krichauffianus ), narrower stipules (0.1–0.17 mm wide, cf.> 0.16 mm in H. krichauffianus ), adaxial leaf lamina colour (green to dark green, cf. typically silvery-white in H. krichauffianus ), free or slightly basally fused epicalyx lobes (fused for up to 0.5 mm, cf. fused for 1–4 mm in H. krichauffianus ) that remain straight in fruiting specimens (cf. recurved or incurved 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 ), and with a central and two marginal flaps of tissue associated with the hilum (cf. with only two marginal flaps in H. krichauffianus ). Hibiscus verecundus has a low usually decumbent habit, whereas in H. krichauffianus the stems are mostly erect or ascending. The habitat of H. verecundus is also completely different from that of H. krichauffianus , the former occurring in woodlands, forests and shrublands (rarely vine-thickets), whereas the latter occurs in more arid environments, typically on sand dunes.

Populations of the highly variable species Hibiscus sturtii and H. leptocladus occur within the distributional range of H. verecundus and could possibly be confused with this. Both H. sturtii and H. leptocladus represent species complexes that are currently undergoing taxonomic revision. Members of the H. sturtii complex have epicalyx lobes that are distinctly fused basally for> 4 mm (or if rarely less then the epicalyx lobes are never narrowly linear), whereas in H. verecundus the epicalyx lobes are free at the base or virtually so. The leaves of H. sturtii var. campylochlamys F.Muell. ex Benth. are similar to those of H. verecundus and the two taxa could be confused when flowers are lacking. Members of the H. leptocladus complex differ from H. verecundus in the erect or ascending habit, petals with a dark basal spot, capsules that never have a dense covering of appressed hairs throughout and the non-appressed seed hairs.

Notes

Due to the risk of damaging the few open flowers present on herbarium specimens (three specimens), some measurements, particularly of the androecium and gynoecium, are based on a small sample and may not truly reflect the range of variation in this species. Only chasmogamous flowers were seen in this species though an extensive field-based investigation has not been undertaken. This contrasts with Hibiscus krichauffianus that can have cleistogamous flowers.

Figures

Fig. 3. Seeds of the four morphotypes. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: C.J.Brodie & P.J.Lang 3402, AD 249644); (b) morphotype B Hibiscus verecundus (voucher: R.J.Fensham 2991, BRI AQ653057); (c) morphotype C Hibiscus calcareus (voucher: P.Hudson s.n., AD 98321044); and (d) morphotype D Hibiscus sp. Belele (voucher: D.W.Goodall 3417, PERTH 3427285). Scale bar: 1 mm.

Fig. 2. Example herbarium specimens of the four morphotypes of H. krichauffianus sens. lat. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: C.J.Brodie & P.J.Lang 3402, AD 249644); (b) morphotype B Hibiscus verecundus (voucher: R.J.Fensham 2991, BRI AQ653057); (c) morphotype C Hibiscus calcareus (voucher: P.Hudson s.n., AD 98321044); and (d) morphotype D Hibiscus sp. Belele (voucher: D.W.Goodall 3417, PERTH 3427285). Scale bar: 2 cm.

Fig. 4. Habit of morphotypes A–C. (a) Morphotype A Hibiscus krichauffianus sens. strict. (voucher: D.E.Albrecht 16356, CANB; images: Dave Albrecht); (b) morphotype B Hibiscus verecundus (voucher: T.G.B.McLay TM333, CANB; images: Mike Bayly); and (c) morphotype C Hibiscus calcareus (voucher: D.E.Albrecht 16345, CANB [holotype]; images: Dave Albrecht).

Fig. 1. Distribution map for the four morphotypes of H. krichauffianus sens. lat. in Australia. Distributions are based only on material viewed by the authors. Morphotype A: Hibiscus krichauffianus sens. strict., grey squares; Morphotype B: Hibiscus verecundus, orange circles; Morphotype C: Hibiscus calcareus, blue triangles; Morphotype D: Hibiscus sp. Belele (voucher: D.W.Goodall 3417), black crosses.