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Hibbertia acaulothrix Toelken
Family Dilleniaceae
Hibbertia acaulothrix Toelken APNI*

Description: Erect shrubs up to 1.1 m tall, with several stems; branches ridged to flanged from the leaf base; pubescent with persistent, dense multiangulate fascicled hairs.

Leaves cuneately oblong-oblanceolate, 6−15 × 2−5 mm, flat, entire; upper surface distinctly grooved along the central vein; vestiture moderately dense with spreading to antrorse fascicled hairs becoming tuberculate; lower surface with central vein broader and often raised above revolute margins, velutinous with erect to spreading multiangulate broad-based fascicled hairs; apex usually truncate-emarginate, rarely rounded with recurved vein-end; base gradually constricted into indistinct petiole, 0–0.3 mm long. Leaves without axillary tufts of hairs. Slightly discolourous; juvenile leaves (coppicing growth) larger but similar to normal leaves, entire, with finer and larger hairs.

Flowers single, terminal, sessile or almost so, often on lateral shoots; bracts linear-oblanceolate to linear-spathulate, 8−10 × c. 2 mm, usually longer than outer calyx, pointed, ridged, below pubescent or velutinous, above tomentose. Calyx with lobes slightly unequal, linear-lanceolate to oblanceolate, 6−7 × 2.5 mm, scarcely longer than inner calyx, pointed to acute, ridged, outside stubble-like to velutinous along margins, inside puberulous to pubescent on the upper third and the margins; inner calyx lobes oblongovate 4.5−5.5 × 3.1−3.8 mm, acute to cuspidate, scarcely ridged, stubble-like to pubescent on a central band and with fascicled cilia on broad membranous margin, inside glabrous. Petals obovate 7−10 × 5−7 mm long, scarcely bilobed. Stamens 9−13 (plus some staminodes), subequal except for 1 - 3 longer ones, in ± 5 bundles around the ovaries; filaments narrow throughout, 1.3−1.8 mm long, slightly connate basally; anthers narrowly obloid, rarely obloid-ovoid, 1.1−1.3 mm long, 1 - 3 longer ones (1.8−1.9 mm long) in the centre, abruptly constricted above and below. Pistils 2; ovaries obovoid, each with 2 - 4 ovules above one another, hirsute, style attached to dorsal apex of ovary then ± erect such that stigmas are lateral to the upper part of the longer incurved anther(s).

Flowering: October – April.

Distribution and occurrence: Known from several widely separated localities in New South Wales, from Wadbilliga National Park in the Southern Tablelands, through the Nattai-Wollondilly area in the southern Central Tablelands, to the Mt Baker and Mt Coricudgy (Wollemi) area in northern part of the Central Coast and Tablelands.

On sedimentary rocks, recorded growing in Eucalyptus sieberi woodland or associated with Allocasuarina littoralis, Corymbia gummifera, Leptospermum trinervium.
NSW subdivisions: CC, SC, CT
AVH map***

Although the species is at present known only from a few well separated localities, the different populations show little variation. Leaves of young fast growing branches have usually predominantly simple hairs on the adaxial leaf surface and these and at least the larger hairs of the abaxial surface are more or less antrorse. Since a similar trend was found in both H. hermanniifolia and H. spathulata the absence of stalked fascicled hairs in this species is significant. The epithet “acaulo-thrix”, Greek, “stalklesshair” (noun in apposition) refers to the sessile hairs of this species in comparison to those of the very similar H. hermanniifolia.

APNI* Provides a link to the Australian Plant Name Index (hosted by the Australian National Botanic Gardens) for comprehensive bibliographic data
***The AVH map option provides a detailed interactive Australia wide distribution map drawn from collections held by all major Australian herbaria participating in the Australian Virtual Herbarium project.

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