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Electronic Flora of South Australia
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Electronic Flora of South Australia species Fact Sheet

Family: Leguminosae
Acacia brachybotrya

Citation: G. Bentham, Hook. Lond. J. Bot. 1: 347 (1842).

Derivation: brachys (Gr.)--short; botrys (Gr.)--a spike.

Synonymy: Acacia brachybotrya, Acacia dictyocarpa

Common name: Grey mulga

Compact, dense, rounded, spreading, grey-green shrubs 1-3 m high and often the same or more across; branchlets slightly ribbed, not angular, hoary.

Phyllodes obliquely oblanceolate to obovate 1-3.5 cm long, 5-15 mm broad, flat, grey-green, glabrous or silky hairy never completely clothed with silky hairs, young phyllodes silky hairy usually bronze to grey-white, 1-veined with inconspicuous lateral veins; apex obtuse, sometimes mucronate. Glands small on the upper margin near the middle.

Inflorescences axillary, solitary or mostly 2-5 pedunculate heads on a short rachis or common penduncle; flower-heads globular, bright yellow 20-30-flowered; peduncles slender finely pubescent up to 20 mm long; flowers 5-merous.

Legumes linear, straight or slightly curved, 3-7 cm long, 5-6 mm broad, raised and sometimes warted over the seeds, dark brown or somewhat glaucous; margins slightly constricted, thickened, yellowish. Seeds longitudinal or oblique in legume; funicle short, thickened into a clavate aril.

Distribution:  This species is quite common, extending from the west near Fowler Bay across Eyre Peninsula, Yorke Peninsula, Kangaroo Island, Northern and Southern Lofty, Murray and South-Eastern regions. It occurs, mainly in open-scrub vegetation on a variety of soil types. Rainfall 250-500 mm. Also Qld. N.S.W. and Vic.

S.Aust.: NU, FR, EP, NL, MU, YP, SL, KI, SE.

Flowering time: August — November.

SA Distribution Map based
on current data relating to
specimens held in the
State Herbarium of South Australia

Biology: No text

Related taxa: Closely related to Acacia argyrophylla which differs mainly in having longer phyllodes always covered with a dense layer of glossy silky, more or less appressed hairs. A. wattsiana differs in having longer phyllodes, elongated racemes, and usually fewer flowers per head.

Taxonomic notes: A hybrid swarm between A. brachybotrya and A. calamifolia is analysed by Leach & Whiffin (1978). These hybrids could be referred to A. x grayana. The population of plants studied was at Kiata, Victoria of which A. x grayana was clearly intermediate between A. brachybotrya and A. calamifolia on basis of morphology. Hundreds of hybrids occurred amongst several thousand parental plants. On the basis of phyllode morphology the two parents, the hybrid and two possible backcross groups could be recognised. In addition the flavonoid chemical composition of individual plants was studied and the results may be taken as strong evidence for hybridisation though they are too complex to be elaborated here. The pollen in Acacia is in polyads each containing a regular number of pollen grains. The polyads of A. brachybotrya have 8 and those of A. calamifolia have 16 grains without exception. The intermediates ranged between these (many with 12) but even on one plant 8, 12, 16 grains could be found. Not only did the number of grains support the hypothesis of hybridity but the structure of each polyad and pollen fertility was also consistent. Ecologically the scene is complex with some soil preferences for each species apparent, but overlap did occur and there was also overlap of the flowering times but only of a week or so. The hybrids were intermediate in flowering time and tended to favour A. calamifolia (the earlier of the two). The combined results convincingly support the hybrid origin of A. x grayana.

A. brachybotrya is a food plant for the larvae of the butterfly Nacaduba biocellata, Fisher (1978).

A. brachybotrya, A. argyrophylla and A. spilleriana are all closely related and are not always readily distinguished.

Cultivation: The attractive silver-grey appearance makes it suitable for ornamental, hedge, shelter belt or roadside planting. A hardy species suitable for dry country planting. Moderate growth rate.

Author: Not yet available



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