Australian Journal of
Taxonomy
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Type: Saddle between Mount Lesueur and Mount Michaud, 22 Aug. 2020, K.R. Thiele 5633 (holo: PERTH 9261907; iso: AD, CANB)
Erect to somewhat spreading, rather openly branched shrubs to 0.3(–0.4) m high, with few to several stems at base and possibly reseeding after fire; young branchlets glabrous to minutely and sometimes densely pubescent with sub-stellate hairs (but glabrescent), and with short tufts of hairs in the leaf axils, usually distinctly grooved below the prominent hypopetiolar pegs. Leaves spreading, scattered, linear to narrowly ovate, usually gently tapering from base to apex, 12–20(–25) mm long, 1–1.5(–2) mm wide, the margins usually prominently recurved to each other or to the midrib (which is not prominent), especially when dried, the abaxial surface mostly obscured; adaxial surface smooth to obscurely and sparsely tuberculate, glabrous or (rarely) with scattered hooked hairs from the tubercles, with sparse, minute hairs at the base of the lamina and along the margins of the petiole; abaxial surface smooth where visible along either side of the midrib, which is smooth and glabrous; apex acute. Flowers sessile, terminating short-shoots or main stems; flower-subtending bracts 4–6, 3–5 mm long, ovate to triangular, acute, scarious, (neither glossy, firm-textured, rigid nor strongly keeled), deciduous, glabrous except for minutely ciliolate margins. Sepals ovate, 6.5–8(–9) mm long, herbaceous, not glossy; midribs not prominent; outer sepals acuminate, glabrous except for a minutely ciliolate margin; inner sepals similar in size and apex shape to the outer but broader and with scattered, minute sub-stellate hairs. Petals 5, yellow, broadly obovate, 11–12 mm long, emarginate. Stamens 10, all on one side of the gynoecium and curving over it like a hand of bananas; filaments 0.5–1 mm long, fused at the base into a robust claw; anthers rectangular, 2–2.5 mm long, dehiscing by introrse, longitudinal slits. Staminodes (1)2 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.
Other specimens examined (all PERTH): Cockleshell Gully (3043584, 4275616, 5685826, 5685893, 3043908, 3043738); Mount Lesueur (3043452, 3043509, 3043959, 3043878); Mount Michaud (4067495); Mount Peron (3043886); Lake Indoon (3043479). 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:1664541361110#tab_mapView
Diagnostic features. Hibbertia lesueurensis can be distinguished from all other species in the H. aurea-H. crassifolia species group by the combination of glabrous leaves 12–20(–25) mm long that taper to an acute apex, and 4–6 glabrous, rather scarious floral bracts that are 3–5 mm long and not glossy or firm-textured.
Phenology. Has been recorded flowering in late July, August and September.
Distribution & habitat. Restricted to Mount Lesueur National Park (Fig. 3), with the exception of an anomalous specimen from Lake Indoon (see Notes below); occurs in kwongan heathlands on shallow sandy soils over laterite.
Conservation status. Hibbertia lesueurensis is well-protected in, but largely restricted to, Mount Lesueur National Park.
Etymology. From the place-name (Mount) Lesueur.
Notes. Superficially, H. lesueurensis is most similar to H. aurea, sharing with that species robust, sharply acute leaves. The leaves, however, are usually somewhat shorter and less slender than those of H. aurea, and the bracts are fewer (4–6 cf. 6–8 in H. aurea), smaller (3–5 cf. usually 7–9 in H. aurea), and are scarious-herbaceous and not keeled (cf. chartaceous and keeled in H. aurea). It is geographically disjunct from both H. aurea and H. pallida, from the latter of which it can be distinguished by its more rigid, sharply acute leaves.
A single specimen from Lake Indoon has unusually small flowers (bracts c. 2 mm long, sepals 5 mm long, petals 8 mm long) but otherwise is a closest match with H. lesueurensis. Its measurements have not been included in the species description above; further field work is needed to determine if it is an anomalous specimen or belongs to a uniformally small-flowered population that could potentially comprise a separate species.