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Photographer: B.R. Maslin
Photographer: B.R. Maslin
Photographer: B.R. Maslin
Immature pods. Photographer: B.R. Maslin
Botanical name
Acacia minutissima Maslin, Nuytsia 18: 158, fig. 5 (2008)
Description
Diffuse, intricately and openly branched, low-spreading (sometimes semi-prostrate) shrubs 0.3-1 (-1.5) m tall and at least 1-3 m across, stem dividing just above ground level into ±horizontally spreading branches which sometimes produces a pseudo-bonsai growth form, oldest plants having a somewhat craggy appearance due to persistent, short lateral branches which are denuded of phyllodes. Bark light grey, slightly roughened. Branchlets terete, finely ribbed (rib most evident for a short distance below insertion of phyllodes), lenticellate (lenticels scattered, circular, dull yellow), glabrous, resinous, slightly viscid when fresh but not sticky when dry, light brown or reddish brown at extremities but soon aging grey. Stipules persistent, erect and appressed to branchlets, enveloped and often obscured by resin on young branchlets, triangular, 0.5-1 mm long, 0.4-0.5 mm wide at base, slightly thickened. Phyllodes asymmetrically elliptic to obtriangular, broadest at or above the middle, lower margin ±shallowly convex or sometimes almost straight, the upper margin longer than lower and markedly convex or angled at the gland, 3-6 (-7) mm long, 2-3 mm wide, length: width = 1-1.6, glabrous , smooth, green; midrib ±evident (at least when dry), central or slightly excentric, sometimes with a less pronounced second nerve on upper side of midrib extending from the pulvinus towards the gland; apices abruptly or more commonly gradually narrowed to a short-acuminate apex and terminating in a distinct, rigid, subulate, pungent, straight, brown point 0.5-1 mm long. Gland situated on upper margin of phyllode 2-4 mm above the base (at, or above, the centre of the phyllode). Inflorescences simple, 1 per axil; peduncles glabrous, 6-8 mm long, red (at least when fresh), base ebracteate; heads globular, densely 40-50-flowered, 5 mm in diameter when fresh, golden; flower buds dull red. Bracteoles spathulate and sparsely hairy, c. 1 mm, claws linear, the laminae inflexed, widely ovate, c. 0.3 mm wide and slightly thickened. Flowers 5-merous; sepals 2/3 to ¾ length of corolla, free, linear-spathulate, sparsely hairy (morphology same as bracteoles); petals c. 1.5 mm long, glabrous, nerveless. Pods (old fruiting valves) linear to narrowly oblong, flat but shallowly rounded over seeds, not or very shallowly constricted between seeds, 10-40 mm long, 3-4 mm wide, firmly chartaceous, sub-straight to slightly curved, glabrous, dark brown (pods maroon-coloured when first initiated), marginal nerve yellow to light brown. Seeds not seen but funicles very short (c. 1 mm long), thread-like and persisting on inside of pods.
Characteristic features
Intricately and openly branched, low-spreading glabrous shrubs. Bark light grey, slightly roughened. Branchlets lenticellate, resinous (slightly viscid when fresh but not sticky when dry), light brown or reddish brown at extremities. Stipules persistent, very small (0.5-1 mm long), erect, enveloped and often obscured by resin on young branchlets. Phyllodes asymmetrically elliptic to obtriangular, broadest at or above the middle, lower margin ±shallowly convex or sometimes almost straight, the upper margin longer than lower and markedly convex or angled at the gland, small (mostly 3-6 x 2-3 mm), midrib central or slightly excentric; apices normally short-acuminate and ending in a distinct, rigid, pungent, brown point. Inflorescences simple, 1 per axil; peduncles short (6-8 mm long), red when fresh, base ebracteate; heads globular, 40-50-flowered. Pods (old fruiting valves) 10-40 mm long, 3-4 mm wide, linear to narrowly oblong, not or very shallowly constricted between seeds, flat but shallowly rounded over seeds, firmly chartaceous. Funicle not expanded into an aril.
Distribution and ecology
Occurs in north-central Western Australia where it extends from the eastern extremity of the Pilbara (east of Balfour Downs Station) east to the Little Sandy Desert to the general vicinity of Lake Disappointment in a series of discontinuous populations. This species was noted under A. maitlandii in Maslin (1981 and 2001a) where it was erroneously referred to as being recorded from the Gibson Desert. In the Pilbara A. minutissima occurs only in the far southeast of the region where it is found in a few localized populations to the east of Balfour Downs Station; it is not uncommon in the places where it occurs. Most commonly grows on sand or loam (sometimes with a gravely mantle) on plains or in swales between sand dunes, in shrub steppe with a spinifex hummock grassland understorey (the spinifex hummocks often overtops plants of A. minutissima).
Flowering and fruiting period
Because of the paucity of specimens it is difficult to determine the phenology of this species. Flowering commences in mid-July or early August and probably extends to about September. Although mature pods and seeds have not been seen they would be expected to occur in November and perhaps early December.
Taxonomy
Acacia minutissima was noted as a variant under A. maitlandii in Maslin (1981, 2001a and 2001b) and was until recently known by its phrase name Acacia sp. Talawana (B.R. Maslin 8540).
Affinities
Acacia minutissima is related to, and superficially resembles, A. subtiliformis which is most readily distinguished by its growth form (tall, spindly, wispy, singled-stemmed shrubs), branching pattern (the ultimate branchlets are longer, less rigid and not as divaricately divided) and its phyllodes which are slightly smaller (mostly 2-3.5 mm long and less than 2 mm wide) and differently shaped (most obvious is that the phyllodes of A. subtiliformis are never obtriangular, their upper margin is less prominently convex and is never angled at the gland, and the apex is less acuminate with a slightly shorter terminal cusp). These two species are not known to grow together. Acacia minutissima and A. subtiliformis are both related to A. maitlandii which is most readily recognized by its much longer phyllodes (i.e. 7-25 mm).
Notes
Acacia minutissima is probably killed by fire and regenerates from seed.
Conservation status
Not considered rare or endangered. However, it is noted that the species is currently not known from the Western Australian conservation estate.
Origin of name
The botanical name is derived from the Latin minutus (little, small) and the adjectival superlative -issimus (very), in reference to the extremely small phyllodes which characterize this species.
References
Maslin, B.R. (1981). Acacia. pp. 115-142. In: J. Jessop (ed.) Flora of Central Australia. pp. 537. (A.H. and A.W. Reed: Sydney.)
Maslin, B.R. (2001a). Acacia. In: A.E. Orchard and A.J.G. Wilson (eds) Flora of Australia. Volume 11A. pp. 536. (ABRS/CSIRO Publishing: Australia.)
Maslin, B.R. (coordinator) (2001b). WATTLE Acacias of Australia. CD ROM. (Australian Biological Resources Study: Canberra, and the Department of Conservation and Land Management: Perth.)