Botanical name

Acacia leeuweniana Maslin, Nuytsia 18: 154, fig. 4 (2008)

Common name

Leeuwen's Wattle (preferred common name) and Spear Hill Wattle

Description

Shapely, obconic, erect trees 4-8 (-14) m tall, with a single trunk or very few trunks from ground level, neither branchlets nor phyllodes pendulous. Juvenile plants (to c. 1 m tall) divaricately branched and possessing short (sometimes only 30-40 mm long), rigid, terete, pungent phyllodes, some of which may occur in clusters on brachyblastic short-shoots (as occurs in some forms of Mulga). Adolescent plants often with a conifer-like appearance, the lower branches ąhorizontally spreading with those higher up ascending, the normally terete phyllodes typically mealy white due to surface wax. Bark 'Minni Ritchi' (i.e. brownish red and exfoliating in narrow shavings that curl retrorsely from each end), aging grey (a short grey stocking occurs around base of stems of oldest plants). Branchlets brittle (snapping easily with a clean break), sometimes with 'Minni Ritchi' bark evident, terete, ribs very obscure, glabrous, light brown or dark red-brown towards extremities. New shoots glabrous, glaucous due to white surface wax. Phyllodes (mature plants) normally linear, 7-12 (-15) cm long, 1-2 (-2.5) mm wide, not especially rigid, straight or almost so, flat, glabrous or sometimes very sparsely and minutely appressed-hairy, green to dull grey-green or sub-glaucous; parallel longitudinal nerves very fine and close together; apices narrowed to a pungent or sub-pungent point; pulvinus finely transversely wrinkled and yellow or brown (when dry). Gland not prominent, situated on upper margin of phyllode 0-1 mm above the pulvinus. Inflorescences simple, 2-6 per axil; peduncles 5-10 mm long, glabrous or (especially at base) sometimes minutely and silvery sericeous, resinous (but not sticky); spikes 10-20 mm long (when dry), light golden, the flowers not especially densely arranged along the glabrous receptacle. Bracteoles very small and insignificant, c. 0.5 mm long. Flowers 5-merous, buds quite large; calyx about Ŋ (or slightly more) length of corolla, gamosepalous, divided for about ŧ or less its length into broadly triangular, sparsely ciliolate lobes; calyx tube nerveless, glabrous or almost so, ąbroad-based (c. 1 mm wide); petals 1.5-2 mm long, glabrous, very obscurely 1 nerved. Pods broad-linear, 3-10 cm long, 6-8 mm wide, flat, no internal partitions, coriaceous-crustaceous to ąsub-woody, shallowly (occasionally a few strongly) curved, glabrous, resinous (but not sticky), very obscurely and sparingly longitudinally nerved, greyish light brown (exterior), dark red-brown (interior), the marginal nerve often visible but not prominent. Seeds longitudinal in pods, obloid or sometimes obloid-ellipsoid, large (7-11 mm long and 3.5-5.5 mm wide), flattened (1.5-2 mm thick), slightly shiny, brown (commonly tinged greyish); pleurogram 'u'-shaped to 'v'-shaped with a wide opening towards the hilum, often bordered by a diffuse band of dull yellow tissue; areole small, c. 1 mm long and 0.8-1 mm wide; funicle expanded into a very small terminal aril.

Characteristic features

Shapely, obconic trees with neither branchlets nor phyllodes pendulous, adolescent plants often with a conifer-like appearance. Bark 'Minni Ritchi' (i.e. brownish red and exfoliating in narrow shavings that curl retrorsely from each end), a short grey stocking occurs around base of stems of oldest plants. Branchlets brittle (snapping easily with a clean break). Phyllodes (mature plants) linear, long and narrow (mostly 7-12 cm x 1-2 mm) flat, straight or almost so, green to dull grey-green or sub-glaucous, not especially rigid, parallel longitudinal nerves very fine and close together, apices pungent or sub-pungent. Spikes light golden, the flowers not especially densely arranged. Calyx about Ŋ (or slightly more) length of corolla, shortly dissected into broadly triangular lobes. Pods broad-linear, 6-8 mm wide, mostly shallowly curved, coriaceous-crustaceous to ąsub-woody, flat. Seeds large (7-11x 3.5-5 mm), flattened. Confined to granite outcrops.

Distribution and ecology

Known from only two granite outcrops in the central Pilbara region of northwest Western Australia. It is common in the places where it occurs. Grows in skeletal gritty granitic soil over massive granite.

Flowering and fruiting period

Flowers have been recorded in April/May (during which time some plants may also be sterile) and also late October. It is quite possible that this species flowers in response to the timing and intensity of rainfall events. Pods with mature seeds have been collected from mid to late-October.

Affinities

Acacia leeuweniana is most closely related to A. cyperophylla which comprises two varieties, only one of which occurs in the Pilbara region, namely, A. cyperophylla var. omearana (which is rare in the region). The typical variety (var. cyperophylla) is widespread from the Ashburton district south of the Pilbara eastwards through Western Australia to South Australia, Northern Territory and Queensland. Acacia cyperophylla var. omearana is distinguished from A. leeuweniana by its distinctively pendulous branchlets and phyllodes, normally terete phyllodes and by the fact that it grows along watercourses (not granite hills as does A. leeuweniana). Acacia leeuweniana is also related (but more distantly) to A. rhodophloia (see that species for distinguishing features).

Conservation status

Acacia leeuweniana is a Priority 1 taxon on the Department of Environment and Conservation's Declared Rare and Priority Flora List.

Origin of name

This handsome new species is named in honour of Stephen van Leeuwen, Research Scientist with the Department of Environment and Conservation, in recognition of the major contribution that he has made to our understanding of the Pilbara flora. Stephen has worked in the Pilbara for 25 years and apart from his extensive documentation and collections of plants of the region during this period he has facilitated the work of many other people through his guidance (technical, scientific and in the field) and advice. Stephen is in charge of the botanical component of the comprehensive Pilbara Biological Survey that is currently in progress.