Hibbertia williamsiorum K.R.Thiele sp. nov.

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WA: Jurien Bay Road 1.6 km W of Brand Highway, 22 August 2020, K.R.Thiele 5631 (holo: PERTH 9261699; iso: AD, CANB)

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Spreading shrubs to 0.5 m high, multi-stemmed at base and resprouting after fire; young branchlets glabrous except for tufts of short hairs in the leaf axils, rarely with minute, scattered, sub-stellate hairs. Leaves spreading, scattered, narrowly oblong to narrowly ovate, (3.5–)5–8(–12) mm long, 1–1.5 mm wide, thick-textured, usually shallowly incurved, the margins strongly recurved to the often somewhat sunken midrib or sometimes to each other, obscuring the abaxial surface; adaxial surface tuberculate (rarely almost smooth), glabrous or with minute, sub-stellate hairs or longer, straight or rarely hooked simple hairs from the tubercles, usually sparsely pubescent at the base and on the petiole, the margins of which are usually minutely ciliate; abaxial surface densely papillate whee visible along either side of the smooth midrib; apex obtuse to subacute, the midrib scarcely excurrent. Flowers sessile, terminating short-shoots or main stems; flower-subtending bracts 7–11, broadly ovate, usually shouldered below a distinct terminal point, scarious, chestnut-brown, 7–11 mm long, glabrous except for prominently white-ciliate margins, the lowermost grading to the leaves. Sepals broadly ovate, 6–8.5 mm long; midribs not prominent; outer sepals broadly acute, mostly glabrous except for white-ciliate margins; inner sepals similar in size and apex shape to the outer but broader and with minute sub-stellate hairs. Petals 5, yellow, broadly obovate, 8–12 mm long, emarginate. Stamens 10, all on one side of the gynoecium and curving over it like a hand of bananas; filaments 0.7–1 mm long, fused at the base into a robust claw; anthers rectangular, 2–2.5 mm long, dehiscing by introrse, longitudinal slits. Staminodes 2(–4) either side of the stamens. Carpels 2; ovaries compressed-globular, densely pubescent; styles inserted excentrically on the carpel apex, parallel and curved beneath the stamens, 1.8–2 mm long. Ovules 2 per carpel. Fruiting carpels and seeds not seen.

Selected specimens examined (all PERTH): Badgingarra National Park (6313078), Boothendara Creek (3069710), Coomalloo Nature Reserve (6947271), Gillingarra (7483392), Mogumber (3045862, 3069141), Moore River National Park (5684846), Warradarge (5423562), Yandin Hill (6313019, 5684803). For full specimen details, see the following batch search of the ALA for this set of specimens: https://biocache.ala.org.au/occurrences/search?q=qid:1665056873072#tab_mapView

Diagnostic features. Distinctive within the Hibbertia crassifolia-H. aurea species group in having thick-textured, short, relatively broad leaves (3.5–12 × 1–1.5 mm) that are usually adaxially glabrous, with the lamina tightly butted against the thick, prominent midrib, the abaxial surface (where visible) densely papillate, and flowers with 7–11, broadly ovate, scarious, chestnut-brown bracts, some of which at least are usually distinctly shouldered below a prominent terminal point.

Phenology. Flowers from July to October with a peak in September.

Distribution & habitat. Occurs from Warradarge to near Bindoon and Gingin (Fig. 8), in kwongan, Banksia woodlands and Eucalyptus todtiana shrublands on white or grey acid sands usually over laterite, with one record from yellow, limestone-derived sands.

Conservation status. Hibbertia williamsiorum is widely distributed, including in a number of national parks and nature reserves, and is not considered to be under threat.

Etymology. Named in honour of Don and Joy Williams, from Hi-Vallee farm near Warradarge. Don and Joy have promoted the appreciation and conservation of the flora of the Badgingarra-Eneabba area for many years, through their wildflower tourism venture at Hi-Vallee. They generously helped with their extensive local knowledge and with guidance and hospitality during field work to ascertain whether Hibbertia williamsiorum and H. ericoides were recognisable as distinct species; both H. williamsiorum and H. ericoides occur on Hi-Vallee, and field work there helped clinch their recognition.

Notes. Superficially very similar to H. ericoides, from which it is most readily distinguished by its floral bracts, which are usually more than half the length of the calyx, scarious, brownish to chestnut, readily deciduous (falling very readily while dissecting rehydrated flowers), and broadly ovate with an acuminate apex, the margins in at least some bracts rather abruptly shouldered below the apex (cf. bracts herbaceous to chartaceous, pale-coloured, ± half the length of the calyx, persistent, narrowly ovate to narrowly triangular and tapering evenly to an acute apex in H. ericoides). The bracts in both species have white-ciliolate margins, but because of the difference in colour the cilia are more prominent in H. willismsiorum than in H. ericoides. There is also a subtle difference in habit in the field, with H. williamsiorum having a slightly stouter habit than H. ericoides with the flowers borne on shorter, stouter short-shoots, and slightly broader leaves. While leaves of H. ericoides are always glabrous or at most have minute sub-stellate hairs from the tubercles, many specimens of H. williamsiorum have sparse, long, simple hairs from the tubercles.

Prior to this treatment, specimens of H. williamsiorum were mostly assigned to H. crassifolia on account of the relatively obtuse leaves. It differs very clearly from that species in having leaves that are abaxially papillate (the papillae usually visible between the margins and midrib) rather than cottony-pubescent.