Botanical name

Acacia drepanocarpa (variant) [phrase name: Acacia sp. Nalgi (N.T. Burbidge 1317)]

Description

Openly branched, obconic multi-stemmed glabrous shrubs 1-3 m tall. Bark grey, smooth. Branchlets marked with crenulate resin ribs (observe at x10 magnification) at extremities, yellow or yellow-green. Phyllodes narrowly elliptic to narrowly oblong-elliptic, (3.5-) 5-7 (-8.5) cm long and 3-5 mm wide, l: w = 7-17, erect, mostly shallowly to moderately incurved, some straight, dull pale green to sub-glaucous; with 3-8, rather widely spaced, raised (when dry) resinous longitudinal nerves, the central one usually slightly more pronounced than the rest, sometimes with a few obscure, anastomosing minor nerves between them; apex terminated by a thickened hard point. Gland situated on upper margin of phyllode 0-2 mm above the pulvinus. Inflorescences simple, 1 or 2 initiated within axil of young phyllodes towards ends of branchlets; peduncles 4-12 mm long; spikes 10-30 mm long, bright golden, often the old (pale yellow) spikes persist on plants for some time following anthesis, the flowers close together. Flowers 5-merous; calyx shortly dissected into broadly triangular lobes, white membranous. Pods narrowly oblanceolate, narrowed towards the base, 5-8 cm long, 6-10 mm wide, erect, woody, opening elastically (and explosively) from the uncinate apex with the dehisced valves recurved, obliquely nerved, bright light green just prior to maturity but yellow at maturity. Seeds oblique and seated in shallow yet distinct chambers, 4-5 mm long, 2.5 mm wide, slightly shiny, mid-brown; pleurogram bordered by a narrow band of dull yellow tissue; funicle-aril straight, white and narrowly turbinate.

Characteristic features

Branchlets yellow or yellow-green and marked with crenulate resin ribs (observe at x10 magnification) at extremities. Phyllodes mostly 5-7 cm long, narrow (3-5 mm), l: w = 7-17, with few, rather widely spaced longitudinal nerves which are raised when dry. Spikes bright golden, the flowers densely arranged. Calyx white membranous. Pods flat, narrowed towards the base, opening elastically from the apex with the dehisced valves recurved. Seeds oblique in pods; funicle-aril straight, white and narrowly turbinate.

Distribution and ecology

Occurs in northwest Western Australia where it is found in the vicinity of Shay Gap at the northern boundary of the Pilbara region; it extends to Cape Keraudren then northwards to Nalgi Station (inland of the Eighty Mile Beach). It is often common in the places where it occurs. Grows in red Pindan sand or loam, on flats or low dune country in open Acacia shrubland (with species such as A. ancistrocarpa, A. hilliana, A. adoxa var. adoxa and A. sericophylla) with spinifex ground cover.

Flowering and fruiting period

Flowers in June and July (possibly also May but there are no specimen records to verify this). Pods with mature seeds have been collected in early and mid-October; it is possible that the fruiting period could extend to early November.

Variation

Invariate.

Taxonomy

The taxonomic status of the species A. drepanocarpa in Western Australia needs to be reassessed. The variant described above is possibly intermediate (both geographically and in phyllodes) between A. drepanocarpa subsp. drepanocarpa and A. drepanocarpa subsp. latifolia. Acacia drepanocarpa subsp. drepanocarpa has long, narrow phyllodes (mostly 1-2 mm wide) and occurs at the western edge of the Great Sandy Desert (it is commonly seen along North West Coastal Highway in the vicinity of Anna Plains and Frazier Downs stations) but it does not reach the Pilbara region. Acacia drepanocarpa subsp. latifolia is rare in the Pilbara, reaching just the northeastern edge of the region in the vicinity of Gregory Range (about 150 km southeast of Shay Gap; it is most obviously distinguished from A. drepanocarpa (variant) by its generally broader phyllodes that measure (6-) 8-12 mm wide.

This variant has been given the phrase name "Acacia sp. Nalgi (N.T. Burbidge 1317)" at the W.A. Herbarium.

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is derived from the Greek drepanon (sickle) and karpos (fruit), presumably because the pods were originally described by Ferdinand von Mueller as 'subfalcate' (i.e. slightly curved). However, this would seem to be an inappropriate name for this species as the pods are more typically straight (except following dehiscence where the pod valves are recurved).