Botanical name

Acacia kempeana F. Muell., Chem. & Druggist Australas. Suppl. 5 (51): 26 (1882)

Common name

Witchetty Bush (preferred common name), Wanderrie Wattle and Granite Wattle

Description

Obconic or rounded, multi-stemmed shrubs 1.5-5 m tall and up to 4-5 m across, growing out to a small tree about 5 m tall with a single trunk (dividing at about 0.5 m above the ground into two main stems). Bark grey, finely longitudinally fissured or fibrous towards base of mature trunks otherwise smooth to branches. Branchlets glabrous. New shoots bright green, shiny, resinous but not sticky. Phyllodes narrowly oblong-elliptic to oblong-oblanceolate, broadest at or above middle and narrowed towards the base, 4-10 cm long, (5- ) 8-12 (-18) mm wide, l: w = 4-17, coriaceous, erect, straight or shallowly incurved, glabrous, dull green to slightly greyish green or pale sub-glaucous ; parallel longitudinal nerves numerous, fine, close together (not anastomosing or with very occasional anastomoses) and of uniform prominence or the central nerve slightly more evident than the rest; apex rounded to obtuse. Gland not prominent, situated on upper margin of phyllode 0-1 mm above pulvinus. Inflorescences simple, 1 or 2 within axils of phyllodes; peduncles 5-12 (-15) mm long, glabrous; spikes 10-35 mm long, bright golden but often drying dull orange, the flowers not especially arranged (best observed in buds). Flowers 5-merous; calyx shortly dissected, glabrous or hairy on lower half. Pods oblong to narrowly oblong, (1.5-) 2-4 (-7) cm long, 8-12 mm wide, flat but slightly raised over seeds, not or scarcely constricted between seeds, papery to thinly coriaceous, finely transversely reticulately nerved, glabrous, dark brown, with a basal stalk 5-10 mm long. Seeds transverse to oblique in pods, obloid to obloid-ellipsoid, 3.5-4 mm long, about 2-3 mm wide, shiny, very dark brown to black; funicle folded below a enlarged fleshy aril which is presumably white when fresh but dull yellow when dry.

Characteristic features

Shrubs multi-stemmed and (except the calyx) glabrous. Phyllodes oblong-elliptic to oblong-oblanceolate, mostly 4-10 cm long and 8-12 mm wide with l: w = 4-17, straight to shallowly incurved, apex rounded to obtuse , very finely multistriate with the parallel nerves very close together and more or less of uniform prominence. Spikes pedunculate (peduncles mostly 5-12 mm long). Pods relatively broad (8-12 mm), flat, papery, finely reticulately nerved, with a distinct basal stalk. Seeds �transverse in pods.

Distribution and ecology

Acacia kempeana is a widespread arid zone species that occurs in all mainland States except Victoria and New South Wales. Within the Pilbara it is found in the Hamersley Range from near Munjina and West Angelas west to near Quarry Hill (about 100 km west of Tom Price). A few specimens from Balfour Downs and Noreena Downs stations (east of Newman) may possibly be A. kempeana but their phyllodes are more acute than normal; the identity of these plants needs further investigation. Grows in stony loam or clay-loam in hilly country, often along seasonal watercourses. In the Quarry Hill area west of Tom Price populations are located on decomposing granitic sandy soils.

Flowering and fruiting period

Seemingly flowers and fruits in response to timing and intensity of rainfall. The main flowering flush is from March to May/June (presumably associated with summer rainfall) with the resulting pods maturing in late September. It is possibly that a second flowering flush occurs around July-August (presumably associated with winter rainfall) but it is not known when the pods from this flowering event reach maturity (perhaps around October/November).

Variation

Acacia kempeana in the Pilbara displays a wide range of variation, especially in phyllode dimensions. Acute phyllodes forms are noted under Distribution and ecology.

Taxonomy

Acacia kempeana belongs to a taxonomically complex small group of species of which five are found in the Pilbara region, namely, A. adsurgens, A. atkinsiana, A. kempeana, A. rhodophloia and A. sibirica. In the Pilbara the situation is further complicated because several of these species seemingly hybridize, and also because both A. sibirica and A. kempeana display extreme variation within the region. The above-mentioned species are characterized by their flat, finely multi-striate phyllodes with the nerves very close together, flowers are arranged in obloid or cylindrical spikes, calyx shortly dissected and flat, thin-textured pods.

The above description of A. kempeana is based entirely on Pilbara occurrences of this widespread species.

Affinities

Acacia kempeana is most closely allied to A. sibirica (with which it sometimes grows) which is perhaps somewhat arbitrarily distinguished in having narrower pods (mostly 3-5 mm wide, occasionally 7 mm) with �longitudinal seeds, and narrower, more elongate phyllodes (mostly 1-5 mm wide with l:w = 8-60). Although some phyllodes on specimens of A. kempeana may be as narrow as 5 mm wide, they are almost always accompanied by others that are at least 8 mm wide, and where pods are present they are at least 8 mm wide. However, not every Pilbara specimen that is referable to the A. kempeana - A. sibirica complex can be confidently placed in one or other of these species using these phyllode and pod characters. Further study of these two variable species in needed, not only to elucidate their patterns of morphological variation, but also to clarify the taxonomic boundaries between them.

Notes

In the Pilbara region Witchetty Bush has been observed sprouting from lateral roots following fire or damage caused by track clearing and maintenance, especially in sites with shallow granitic soil.

In Northern Territory light grazing of plants of A. kempeana can stimulate new growth when conditions are favourable, however, over-grazing will often cause death; severely grazed plants assume a tree form as the outer branches are removed (Askew and Mitchell 1978). These authors also report that although A. kempeana has good palatability it has low nutritive value as it contains less protein and minerals than other Acacia species. Mitchell and Wilcox (1994) report A. kempeana as having a crude protein content of about 8 per cent and note that while stock will graze the species during drought it is regarded as a 'last resort' fodder.

Latz (1999) reports that Witchetty Bush was an important species for indigenous peoples of central Australia. The seed was used as a source of food, the stem and roots were used to fashion fighting and fish spears, the phyllodes and inner bark from the roots were used for medicinal purposes, and very importantly, the large, tasty and nutritious Witchetty grubs are found in its roots. Latz (1999) provides an excellent description of Witchetty grubs; they can grow larger than a person's thumb and have a flavour somewhere between egg yolk and almonds.

Conservation status

Not considered rare or endangered.

Origin of name

The botanical name is from the Rev. Friedrich Adolph Hermann Kempe (1844-1928) co-founder of the Hermannsburg Mission in the Northern Territory, who sent about 600 plant specimens to Ferdinand von Mueller in Melbourne, including the type of A. kempeana which was gathered in 1879 from the Finke River. Note: The application of the Kurrama name Pilarri to A. kempeana by Wangka Maya (2001) is probably a mistake resulting from a misidentification of a plant of A. atkinsiana.

References

Askew, K. and Mitchell, A.S. (1978). The fodder trees and shrubs of the Northern Territory. Extension bulletin No. 16. pp. 84. (CSIRO Division of Primary Industry: Alice Springs.)

Latz, P.K. (1999). Pocket Bushtucker: a field guide to the plants of Central Australia and their traditional uses. pp. 215. (IAD Press: Alice Springs.)

Mitchell, A.A. and Wilcox, D.G. (1994). Arid shrubland plants of Western Australia. Edn. 2. pp. 478. (University of Western Australia Press in association with the Department of Agriculture: Perth.)

Wangka Maya (2001). Kurrama Wordlist and Sketch Grammar. pp. 193. (Wangka Maya Pilbara Aboriginal Language Centre: South Hedland.)