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Electronic Flora of South Australia species Fact Sheet

Family: Fabaceae
Acacia mearnsii

Citation: E. de Wildeman, Plant. Bequert. 3:61 (1925).

Derivation: mearnsii--in honour of Edgar Alexander Mearns (1856-1916), an American who collected the type specimen in East Africa. It was thought by de Wildeman to be endemic there.

Synonymy: A. decurrens sensu Bak.f., Leg. Trop. Afr. 3:853 (1930) saltem pro parte, non Willd., sensu stricto. A. decurrens var. mollis Lindley, Edwards Bot. Reg. 5:t. 371 (1819). A. mollissima sensu auct. mult. Benth., Hook. Lond. J. Bot. 1:385 (1842). Racospermum mearnsii (DeWild)Pedley, Bot. J. Linn. Soc.(London) 92:249 (1986).

Common name: Black wattle

Small, spreading trees 7-10 m high, canopy rounded or conical with branches almost to the ground; branchlets angular, pubescent; bark smooth and greenish-brown on young branchlets, blackish and rough on main trunks, often exudes a gum.

Leaves bipinnate, all parts softly pubescent; petiole 1-5 cm long, often with a gland above; rachis 4-15 cm long, with a raised gland at the junction of each pinnae pair and usually with additional glands irregularly spaced between the pinnae pairs; pinnae 8-25; pinnules 30-70 pairs, crowded, 1.5-4 mm long, 0.5-0.75 mm broad, linear-oblong, obtuse.

Inflorescences very abundant in long, axillary racemes and panicles; flower-heads globular, pale yellow, fragrant, 20-30-flowered; peduncles golden pubescent, 5-8 mm long; flowers 5-merous.

Legumes broad-linear, 5-10 cm long, 5-8 mm broad, almost moniliform, dark grey-brown to blackish, more or less covered with a fine whitish tomentum. Seeds longitudinal in legume, ellipsoid; funicle short, expanded into an oblique aril.

Distribution:  Occurs in the Southern Lofty region (introduced) and the lower South-Eastern region from Naracoorte southwards in woodland, open forest and tussock grassland. Soils: leached sand with a hardpan, sandy neutral yellow duplex or dark deep porous loam. Rainfall 600-800 mm. Also Qld, N.S.W., A.C.T., Vic. and Tas.

S.Aust.: EP, SL, SE.

Flowering time: September — November.

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

Biology: No text

Related taxa: Acacia dealbata has very similar bipinnate leaves and can be confused with Black wattle. It differs in having glands only at the base of pinnae. A. decurrens differs in its branches angled with wing-like ridges and its dark green leaves with pinnules well separated.

Taxonomic notes: Although A. mearnsii has been considered native to South Australia the earliest specimen at the herbarium is a cultivated one of 1892. It had been listed even earlier (as A. mollissima) in 1859. It was not listed as being cultivated in 1871 and 1878. The earliest specimen from the South-East was from Glencoe in 1917 and from Hindmarsh Valley in 1925. It was spontaneous at Aldgate by 1944. The first collection from Eyre Peninsula was in 1965. This suggests that it may not be native even to the South-East and that it is certainly introduced to the Southern Lofty and Eyre Peninsula regions.

Hendry & van Staden (1982) studied the effects of scarification, dry heat and wet heat on the germination of A. mearnsii. Scarification was the most successful achieving near 100% germination in 4 days compared with almost zero for the controls. In addition abrasion with sand was less effective than treatment with sulphuric acid. Treatment with solvents was not effective.

A. mearnsii is now well established in South Africa. It has been used extensively as a source of tannin, firewood and timber. Although native to eastern Australia, it was named from South African material where it was thought to be native, Ross (1975). It is also locally established in southern Europe. A. mearnsii is now naturalised in New Zealand, Webb et al. (1988).

A monograph on the black wattle was published by Sherry (1971). The Volume is not readily available in South Australia and the copy seen came from the C.S.I.R.O. Forestry & Timber Bureau library in Canberra. Botanical features of the plant are described relatively briefly and most of the book is an account of its cultivation throughout the world. Notes on introduction and use to the countries of Africa, Asia, Europe and America are followed by a detailed account of its use as a plantation crop in South Africa.

Black wattle must be one of the few Australian plants that have had a Research Institute founded on its use and the Wattle Research Institute was established in Natal in 1941. By the late 1960s there were 243,000 ha. (600,000 acres) in cultivation in South Africa with a further 240 ha in Zimbabwe. As a result it is one of the few Australian plants on which there is even elementary knowledge of genetics and tree-breeding.

In 1971 black wattle supplied about 38% of the world's demand for vegetable tans. However the development of chrome tanning is likely to reduce the demand for vegetable tans.

A. mearnsii, because of its rapid growth rate, has been a useful fuel tree in India and Africa. The timber has been used for light wood constructions but is virtually ignored in Australia.

Henderson (1989) has shown that A. mearnsii is one of the most abundant woody invasive aliens in both Savanna and Grassland biomes of the Orange Free State, South Africa.

A manual on wattle growing (in South Africa) was published by Beard (1957) presumably principally on A. mearnsii but this has not been available to us.

The only mistletoe recorded on A. mearnsii in South Australia is Amyema preissii, wire-leaved mistletoe which has a wide host range of Acacia.

Wool may be dyed with all parts of A. mearnsii. The colours may range from grey-fawn to gold depending on the mordants used, Martin (1974).

A. mearnsii was included in Boland et al. (1984) 'Forest Trees of Australia' where a description, illustrations and a map are given.

Cultivation: Prefers high rainfall areas; previously cultivated widely as an important source of tanbark. Fast growth rate.

Author: Not yet available



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