Botanical name

Acacia catenulata subsp. occidentalis Maslin, Nuytsia 18: 145, fig. 2 (2008)

Common name

Western Bendee

Description

Dense, rounded large shrubs maturing to obconic or spreading shapely trees 3-8 (-10) m tall, with a single trunk or having a few trunks (up to about 4) arising from ground level, trunks (and branches) not fluted, with wide-spreading (patent to ascending) lateral branches along main trunks from near ground level (these branches persist, even after they have died, until the plants are very mature), the crowns bushy, often rounded and up to 3-4 (-5) m across. Bark mid-grey to black, longitudinally fissured and fibrous on main trunks, smooth on branches. Branchlets light brown or orange extremities, glabrous except minutely appressed-hairy at ends of at least the young branchlets (observe at x10 magnification), the hairs straight, silvery white and becoming sparser with age. New shoots densely sericeous, the hairs silvery or pale citron when first initiated, silvery and becoming sparser with age. Phyllodes variable, narrowly elliptic or oblong-elliptic to linear-elliptic, occasionally narrowly lanceolate, (4.5-) 6-11 cm long, (3-) 4-8 (-12) mm wide (the shortest and broadest phyllodes appear to occur on young plants), not rigid, wide-spreading, sometimes straight but more typically shallowly to moderately falcately recurved, occasionally imperfectly sigmoid, invested with a sparse to moderately dense layer of minute (difficult to see without magnification), closely appressed, straight, silvery-white hairs which become progressively sparser with age (absent from oldest phyllodes), mid-green to dark-green (with a slight silvery sheen) to distinctly sub-glaucous or dull greyish green; parallel longitudinal nerves very fine, numerous and close together (longitudinal anastomoses very infrequent), the midrib and sometimes a nerve on either side of it slightly more pronounced than the rest; marginal nerve not prominent, very narrow, yellow or occasionally light brown (at least when dry) and not resinous; apices acute; pulvinus 2-3 mm long, finely transversely wrinkled and yellow to brown when dry. Gland very obscure, situated on upper margin of phyllode 0-2 mm above pulvinus, lamina not or only slightly swollen about the gland. Inflorescences simple or rudimentary racemes; peduncles normally 2 per axil with a rudimentary vegetative bud within their angle at anthesis, 2-7 mm long, moderately to densely hairy, sometimes glabrous in fruit, hairs appressed or �spreading; receptacle glabrous or sparsely puberulous (hairs white, �patent); spikes 8-15 mm long (when dry), presumably golden, the flowers rather close together. Bracteoles sub-peltate. Flowers 5-merous, small; sepals linear-spathulate, free to base, about � the length of petals; petals 1.2 mm long, glabrous, very obscurely 1-nerved; ovary densely silvery appressed -hairy. Pods flattened (scarcely raised over the seeds), deeply constricted between seeds, fragile and readily breaking into 1-seeded oblong-elliptic articles at the constrictions, 2-5 cm long, 4-6 (-8) mm wide, thinly coriaceous-crustaceous, glabrous or sometimes minutely appressed-hairy at constrictions, openly reticulate (nerves raised, at least when dry), with a short basal stalk. Seeds longitudinal in the pods, ellipsoid to obloid-ellipsoid, 3.5-5 mm long, 2-3 mm wide, flattened (c. 1 mm thick), dark brown, seed coat thin; areole very small and inconspicuous; funicle thread-like, without an aril or expanded into a very small, terminal aril.

Characteristic features

Rounded shrubs maturing to obconic or spreading shapely trees. Branchlets glabrous except minutely appressed-hairy at ends of at least the young branchlets. New shoots densely sericeous (hairs silvery or pale yellow) when first initiated. Phyllodes narrowly elliptic or oblong-elliptic to linear-elliptic, occasionally narrowly lanceolate, sometimes straight but more typically shallowly to moderately falcately recurved, occasionally imperfectly sigmoid, not rigid, microscopically appressed-hairy but ageing glabrous, parallel longitudinal nerves very fine and close together, marginal nerve not pronounced. Inflorescences simple or rudimentary racemes; peduncles short (2-7 mm), hairy (except sometimes glabrous when in fruit); spikes short (8-15 mm). Sepals free. Pods deeply constricted between seeds and readily breaking into 1-seeded, oblong-elliptic articles at the constrictions, flat, thinly coriaceous-crustaceous, glabrous (sometimes minutely appressed hairy at constrictions), openly reticulate. Seeds flat, seed coat thin and not especially hard, the funicle thread-like and not or scarcely expanded into an aril.

Distribution and ecology

Confined to the Pilbara region of northwest Western Australia, where it extends from the central Hamersley Ranges (around West Angelas) eastwards through the Ophthalmia and Hancock Ranges to Newman; it also occurs on Balfour Downs Station (about 150 km northeast of Newman) and on the old Great Northern Highway between Newman and Nullagine, just north of the Fortescue River on Roy Hill Station. A similar disjunction between the Hamersley Range and the Balfour Downs area occurs also in A. bromilowiana and A. subcontorta. Forms dense populations in many places (regeneration from seed), particularly in circumstances where the ground cover is not spinifex; this occurs especially on the Coondewanna Flats near The Governor (just north of West Angela), Wanna Munna Flats to the north of Giles Point in the Hamersley Range and in the Ethel Creek - Balfour Downs Station area. Occurs on red-brown hardpan flat or gently undulating terrain along diffuse watercourses or colluvial fans, sometimes extending to dry low rocky hills or ridges. It grows on (stony) shallow red-brown sandy loam, clay-loam, deep red loamy duplex soils or self-mulching cracking clays in open to moderately closed Low Woodlands of Eucalyptus victrix and/or with Mulga in the Boolgeeda, Wanna Munna and Coolibah Land Systems (van Vreeswyk et al. 2004).

Flowering and fruiting period

Paucity of flowering and fruiting specimens makes it difficult to accurately determine the phenology of the subspecies. It appears to flower in response to rainfall between December and June, however, not all plants in given populations produce flowers during this period. Pods with mature seeds have been collected between August and October.

Taxonomy

Acacia catenulata comprises two subspecies, subsp. catenulata (which occurs in Queensland and Northern Territory) and subsp. occidentalis (which occurs in the Pilbara).

Affinities

The flat, thin-textured, openly reticulate pods which readily break into 1-seeded articles at the constrictions between the seeds readily distinguish this subspecies from all other Pilbara wattles, however, sterile or flowering plants may possibly sometimes be confused with either A. distans or A. subcontorta. Apart from the pods, A. distans can be recognized by having much longer, interrupted flowering spikes and phyllodes which tend to have a denser indumentum of slightly longer hairs, and A. subcontorta by its �contorted and horizontally spreading branches, generally longer spikes, partially united sepals and its generally straighter and narrower phyllodes with often red margins. Acacia subcontorta and A. catenulata subsp. occidentalis grow together on the Wanna Munna Flats near Giles Point in the Hamersley Range and in the absence of pods care needs to be taken not to confuse the two. Along Jigalong Creek east of the Ethel Creek Station homestead Acacia distans and A. catenulata subsp. occidentalis grow together, although the latter tends to occupy micro-relief positions higher on the alluvial plain. A putative hybrid between A. aneura and A. catenulata subsp. occidentalis occurs between Newman and Jigalong.

Notes

This species is extremely fire sensitive and generally killed under most fire conditions. Lightly scorched plants or those burnt under very cool fire conditions resprout advantageously from the crown, along main stems and branches or from the truck just below the ground level.

Conservation status

Not considered rare or endangered.

Origin of name

The subspecies name is derived from the Latin occidentalis (west, western) in allusion to the geographic location of this taxon relative to the typical subspecies.

References

van Vreeswyk, A.M.E., Payne, A.L., Leighton, K.A. and Hennig, P. (2004). An Inventory and Condition Survey of the Pilbara Region, Western Australia. pp. 423. Technical Bulletin No. 92. (Department of Agriculture: Perth, Western Australia.)