Australian Journal of
Taxonomy
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Type: Western Australia: Between Warrachuppin Rock and Lake Baladjie, near the intersection of the Koorda-Bullfinch Road and Warrachuppin Road, 19 Sept. 2021, K.R. Thiele 5766 (holo: PERTH 9369120; iso: AD, CANB).
Spreading shrubs to 0.6 m high. Young stems sparsely to moderately sericeous with white, crisped, simple hairs. Leaves scattered, sessile, linear, 20–50 mm long, 1–1.5 mm wide, glabrous except at the dilated and slightly stem-clasping base where there are moderately dense simple white hairs on the margins and adaxial surface; margins recurved (when dried, to the midrib or to each other); apex acute with a short, callus point. Flowers single, terminating main stems and lateral short-shoots, sessile, sometimes in few-flowered clusters. Bracts 3–5, pale fawn to whitish; primary bract ovate to elliptic, acute, 5–6 mm long, herbaceous, pubescent abaxially and ciliate-margined; secondary bracts successively more glabrous except for the ciliate margins, the lowermost grading into leaves. Sepals ovate, c. 8 mm long, with abundant coarse, spreading, white, tubercle-based, simple hairs; outer sepals acuminate; inner sepals broader and usually obtuse-apiculate, with membranous, minutely ciliolate margins. Petals 5, yellow, obovate, c. 10 mm long, emarginate. Stamens 32–35, in 5 bundles each of 5–7 stamens; filaments fused in the lower half (the innermost stamen almost free), c. 1.8 mm long; anthers c. 1.5 mm long, narrowly oblong and dehiscing by introrse longitudinal slits; staminodes absent. Carpels 5; ovaries globular, glabrous; styles radiating outward, 2–2.5 mm long. Ovules 1 or 2 per carpel. Mature seeds not seen.
Diagnostic features. Hibbertia leptophylla can be distinguished from all other Western Australian taxa by the combination of very narrow, linear, largely glabrous leaves with expanded, almost sheathing bases; sessile flowers with abundant spreading, white, tubercle-based hairs; stamens in 5 bundles united by their filaments; and 5 glabrous carpels.
Phenology. Has been collected flowering in mid-September.
Distribution & habitat. Known only from a single locality (Map 1), in a narrow strip of vegetation on the outwash flanks of Warrachuppin Rock, between the rock edge and the adjacent (salt) Lake Baladjie, growing in gritty, yellow, sandy soils beneath Eucalyptus loxophleba, Acacia acuminata and A. tetragonophylla.
Conservation status. Known at present from one site, in an unusual habitat.
Etymology. From the Greek leptos (thin, narrow) and phyllon (a leaf), in reference to the distinctively long, narrow leaves.
Notes. Hibbertia leptophylla is clearly closely related to H. glomerosa, sharing with that species leaves with expanded, somewhat sheathing bases; sepals with abundant spreading, white, tubercle-based, simple hairs; sessile flowers with numerous stamens in five bundles fused by their filaments; and 5 glabrous carpels. It differs in having very narrow, almost filiform, leaves.
When the first specimen of H. leptophylla was found amongst sheets of H. glomerosa at PERTH, it was considered that it may represent an unusual, mutated individual. Assessment of all c. 180 sheets of H. glomerosa showed that the specimen was morphologically a wide outlier from the usual range of variation in that species. A visit to the locality of the specimen in spring 2021, however, revealed a population of plants with consistent morphology, all clearly distinct from H. glomerosa populations found less than 1 km away.
Wheeler (2002) described H. glomerosa as having 1-ovulate carpels, while carpels in H. leptophylla may be 1- or 2-ovulate within the same flower. Closer examination of H. glomerosa shows that this applies to that species as well.