Australian Journal of
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Hibbertia arenicola K.R.Thiele, sp. nov.
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Type: Western Australia: Lake King-Norseman Road c. 82 km from Lake King, 15 Sept. 2021, K.R. Thiele 5748 (holo: PERTH 9369074; iso: AD, CANB).

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Spreading to straggling shrubs to 0.5 m high, multi-stemmed at base and resprouting after fire; young branchlets comprising densely packed, thickened, pubescent, persistent leaf bases (hypopetioles). Leaves mostly crowded at the apices of short-shoots, erect at first then spreading, oblong, 4–8 mm long, 1.4–2 mm wide, the margins strongly recurved to the thickened, prominent midrib, obscuring the abaxial lamina; petiole 0.8–1.5 mm long, the hypopetiole thickened, dark brown, glabrous to sparsely pubescent especially on the margins, forming a thickened peg on the stem surface when the leaf is mature, the epipetiole very short, densely curled-pubescent; adaxial lamina not tuberculate, glabrous except for dense, curled-woolly hairs at base (sometimes sparsely hairy throughout when very young); abaxial lamina (visible only by dissection) densely pubescent; abaxial midrib broad, level with or bulging above the margins, glabrous, often with a narrow, central, yellowish sclerenchymatous stripe bordered on either side by green mesophyll; apex obtuse and pungently apiculate. Flowers sessile, terminal on short-shoots, closely subtended by crowded leaves; flower-subtending bracts 6 or 7, reddish brown, scarious (the apex often pale and indurate), narrowly triangular, narrowly acute, the primary bract 2.5–3.5 mm long. Sepals ovate, 5–5.5 mm long, moderately to densely appressed-pubescent; midribs prominent; outer sepals pungently acuminate to shortly mucronate; inner sepals similar to the outer but less acuminate and broader. Petals 5, yellow, obovate, 5.5–8 mm long, deeply emarginate. Stamens 10, all on one side of the gynoecium and curving over it like a hand of bananas; filaments c. 0.5 mm long; anthers rectangular, c. 2 mm long, dehiscing by introrse, longitudinal slits. Staminodes absent. Carpels 2; ovaries compressed-globular, densely pubescent; styles curving excentrically from the carpel apex, 1.2–1.8 mm long. Ovules 4 per carpel. Fruiting carpels and seeds not seen.

Other specimens examined. WESTERN AUSTRALIA: (All PERTH): Mount Gibbs (7313691), Frank Hann National Park (3094065, 9261958, 9261990), near Lake Ace Nature Reserve (6232949).

For full specimen details, see the following batch search of the ALA for the above set of specimens: https://biocache.ala.org.au/occurrence/search?q=qid%3A1695029886183&qualityProfile=ALA&disableQualityFilter=scientific-name#tab_mapView

Diagnostic features. May be discriminated from all other species of Hibbertia in Western Australia that have pungent, non-tuberculate, ericoid leaves by the combination of sessile flowers with shortly pungent, silky sepals, ten stamens, and four ovules per carpel.

Phenology. Flowering specimens have been collected in June, August and September.

Distribution and habitat. Occurs in south-western Western Australia, where known from a few scattered localities between Lake King and 90 Mile Tank in Frank Hann National Park. Occurs on undulating plains on sandy, loamy or somewhat clayey soils over laterite, in proteaceous-myrtaceous kwongan heath dominated by species of Allocasuarina, Hakea, Melaleuca, Micromyrtus, Beaufortia, Banksia, Leptospermum, Isopogon, Petrophile and Callitris.

Conservation status. Hibbertia arenicola is known from only three localities, one of which is in a conservation reserve. Its conservation status should be assessed.

Etymology. From the Latin arena (sand) with the suffix -cola (a dweller, inhabitant), in reference to the sandplain habitat, in contradistinction to the rocky upland occupied by H. axillibarba.

Notes. Hibbertia arenicola and H. erioclada are superficially similar, sharing leaves densely crowded at the apices of short-shoots, leaving closely overlapping, peg-like hypopetioles when they are shed, and with margins recurved to abut the very broad midribs. The former has distinctly pungent sepals and glabrous hypopetioles and leaf laminas (sepals in H. erioclada are obtuse and apiculate, the hypopetioles are densely pubescent, and the leaf laminas are hairy and only tardily glabrescent). Hibbertia axillibarba is also superficially similar, but the midribs in that species are rather weak and the leaf margins are recurved to each other (at least when dried) so that the midrib is hidden (while in H. arenicola and H. erioclada the leaf margins are recurved to and closely abut the broad, prominent midrib).