Acacia mearnsii De Wild.
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Authority
Isley, Duane. 1973. Leguminosae of the United States: I. Subfamily. Mimosoideae. Mem. New York Bot. Gard. 25 (1): 1-152.
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Family
Mimosaceae
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Scientific Name
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Description
Species Description - Unarmed shrub or tree to 20 m. Young growth (unfolding leaves) to tawny or golden velutinous, not becoming glaucous in age; leaf rachises villosulous, leaflets usually glabrate above but ciliate, puberulent beneath or puberulent both surfaces. Leaves bipinnate, greenish; rachis with both "nodal" and interjugary glands; pinnae 10-18 pairs; leaflets contiguous, 24-45 pairs, shortly oblong, nearly symmetric, 1.8-2.2(-2.5) mm long, .5-.8 mm wide, 3-4.5 r. Flowers in cream-yellow heads 6-7 mm diam on peduncles 5-7 mm, in axillary racemes and terminal panicles. Legume oblong, laterally compressed, 4-8 cm long, 5-8 mm wide; margin constricted or not; valves papery, reddish-brown, becoming black, initially pubescent, not glaucous. Funiculus extending ca 90° about seed, folded, arillate.
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Discussion
A. mollissima auct. A. decurrens var. mollis auct. A. dealbata Hort. pro parte A. decurrens var. dealbata Hort. pro parte CN 2n = 26 (Atchison, 1948). This species is usually reported in standard references as A. decurrens var. mollis Lindl. or A. mollissima Willd. It is neither as common nor as aggressive as the related A. dealbata with which it is frequently confused. Jones (1933) contrasts the usual flowering time of A. mearnsii (June) with that of A. dealbata (Feb-March). The specimens I have seen do not entirely confirm this generalization. I have discussed the Acacia mearnsii-dealbata situation under the latter species. I distinguish herbarium material of the two primarily on the basis of foliar glands, secondarily of leaflet shape and pubescence as indicated in the key. The legumes are distinctive but not often present. Phillip & Sherry (1949), studying hybrids between A. decurrens and mearnsii in South Africa (wattle improvement program), tabulated means for several characters of both species. For A. mearnsii, they summarized leaflet length as 3.4 mm, width .7 mm. Comparing the leaflets of U.S. material of A. mearnsii and dealbata, I found the former to be 1.8-2.5 mm (mean 2 mm) long, and .5-8 (mean .6) mm wide. Tindale (1962) says that the leaflets are 1.2-3 mm; thus her mean is possibly about the same as but with a greater range of variance whereas Phillip & Sherry’s material had larger leaflets. These differences probably indicate specificity of genotypes introduced into Africa and the United States. They also possibly illustrate a type of sample-observer interaction that may be common in taxonomic documentation.
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Distribution
Urban California. Cultivated ornamental. March-June. Black wattle. Native of Australia and widely planted in Old World as a source of tannin.
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