Botanical name

Acacia fecunda Maslin, Nuytsia 18: 151, fig. 3 (2008)

Common name

Mosquito Creek Wattle

Description

Obconic shrubs 1.5-3 m tall, with 2-4 main stems (4-5 cm in diameter at base) arising from near ground level, crown open to sub-dense and spreading to about 3 m across. Bark thin, smooth (although with a few longitudinal fractures developed near base of stems on mature plants), grey on main stems, upper branches (and stems of young plants) orange. Branchlets slender, terete except angled at extremities, very finely ribbed, minutely and densely white-hairy (hairs straight or slightly crisped, mostly appressed except sometimes some sub-appressed or patent). New shoots light brown when first initiated due to a microscopic indumentum of irregularly-shaped scales intermixed with silvery non-resin hairs, aging light green. Stipules caducous. Phyllodes narrowly elliptic to oblanceolate, straight and dimidiate to shallowly or moderately falcately recurved, narrowed at base, 8-12 cm long, 10-15 mm wide, wide-spreading to ascending, coriaceous to thinly coriaceous, glabrous or sparsely and minutely appressed-hairy, often slightly resinous (but not sticky), dull or with a very slight sheen, green or bluish green (and sometimes lightly pruinose when young); parallel longitudinal nerves fine with 2 sub-central nerves more evident than the rest, the minor nerves close together and sometimes very few longitudinally anastomosing, the 2 main nerves confluent with one another near pulvinus or ąfree but not confluent with lower margin although situated close to it; marginal nerve narrow, discrete, yellowish to light brown; apex obtuse or acute with a sometimes up-turned apical point; pulvinus 4-5 mm long, distinct, orange when fresh (drying dull yellow to brownish), minutely hairy at least on upper surface, normally finely transversely wrinkled and sometimes shallowly longitudinally grooved or ridged (at least when dry). Inflorescences simple, 2 per axil, new shoots arising from within angle formed by peduncles; peduncles 7-12 mm long, sub-stout, glabrous, scurfy or minutely hairy as on branchlets; receptacle glabrous; basal peduncular bract triangular, c. 1 mm long, caducous; spikes 20-40 (-45) mm long, 5-6 mm wide, light golden, densely flowered. Bracteoles linear-spathulate, c. 1 mm long. Flowers 5-merous; calyx gamosepalous, Ŋ to 3/5 length of corolla, very shortly divided into oblong-triangular lobes, calyx tube minutely white-hairy and not obviously nerved; petals 1.5 mm long, sub-glabrous to appressed -hairy, very obscurely 1-nerved to nerveless; ovary densely minutely villous. Pods prolific, linear, very slightly constricted between seeds and ąshallowly but distinctly rounded over them, 7-9 cm long, 3-4 mm wide, firmly chartaceous to very thinly crustaceous, straight or almost so, sub-glabrous to minutely appressed-hairy (observe indumentum under magnification), brown (darkest over seeds), the marginal nerve narrow and scarcely thickened. Seeds longitudinal in pods, obloid to obloid-ellipsoid, 3.5-4 mm long, c. 2 mm wide, compressed (1 mm thick), dark brown with a satin lustre; pleurogram indistinct, open towards the hilum; areole elongate (c. 2 mm long and 0.5 mm wide); funicle thread-like, abruptly expanded into a small terminal, white aril.

Characteristic features

Obconic shrubs with spreading, ąopen crowns. Branchlets slender, minutely and densely white-hairy. Phyllodes narrowly elliptic to oblanceolate, straight and dimidiate to falcately recurved, narrowed at base, 8-12 cm long, 10-15 mm wide, wide-spreading to ascending, green or bluish green, parallel longitudinal nerves fine with 2 sub- central nerves more evident than the rest, the minor nerves close together; pulvinus 4-5 mm long, distinct, orange when fresh. Spikes 2 per axil, light golden, densely flowered, 20-40 (-45) mm long; peduncles 7-12 mm long, sub- stout. Pods produced in great profusion, 7-9 cm long, 3-4 mm wide, linear, very slightly constricted between seeds and ąshallowly but distinctly rounded over them, thin-textured, sub-glabrous to minutely appressed -hairy. Seeds longitudinal in pods, dark brown with a satin lustre, aril white.

Distribution and ecology

Confined to the Pilbara region of northwest Western Australia where it is known only from a few disjunct populations east of Nullagine (to near the confluence of the Davis and Oakover Rivers) and grows in areas underlain by Mosquito Creek sedimentary rocks. It is likely that further survey of similar habitats will reveal additional populations (but these areas are remote and difficult of access) although it is not expected that this species will be shown to have a particularly extensive geographic range. Acacia fecunda is often common in the places where it occurs and favours water-gaining sites.

Flowering and fruiting period

Flowering specimens have been collected between mid-April and late May and it is probable that some flowers would remain on the plants until about mid-June. Only a single fruiting collection has been made and this was collected around mid-October. It is estimated that mature seed would occur from around late September to about early November.

Affinities

Acacia fecunda appears most closely related to A. gonoclada (which does not occur in the Pilbara) and may superficially resemble A. elachantha, A. hamersleyensis and A. tumida var. pilbarensis. Acacia elachantha is readily recognized by its phyllodes having 3 prominent longitudinal nerves with widely spaced, longitudinally anastomosing minor nerves, seeds with yellow arils and densely hairy new shoots (hairs silver or yellow). Acacia hamersleyensis is most readily recognized by its glaucous to sub-glaucous phyllodes, often larger spikes (3-6.5 cm x 6-8 mm) and most particularly by its broader (5-8 mm), hairy pods with obliquely placed seeds. Acacia tumida var. pilbarensis grow in the same general area as A. fecunda but var. pilbarensis is recognized by its branchlets being glabrous and usually pruinose, inflorescence spikes arranged in racemes and pods which are broader (6-7 mm) and woody.

Notes

Acacia fecunda regenerates from seed following fire or other disturbance (may form dense roadside populations). Plants flower from an early age (when only about 0.5 m tall and probably no older than about one year).

Conservation status

Acacia fecunda is a Priority 3 taxon on the Department of Environment and Conservation's Declared Rare and Priority Flora List.

Origin of name

The species name is derived from the Latin fecundus (fruitful, fertile, prolific) in allusion to the large number of pods produced. The common name acknowledges the Mosquito Creek Basin, a restricted geological feature of Achaean age located to the east of Nullagine that is overlain by the Mosquito Creek Formation. Almost all populations of A. fecunda are restricted to the Mosquito Creek Basin.