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Typical variant. Photographer: B.R. Maslin
Typical variant. Photographer: B.R. Maslin
Typical variant. Photographer: B.R. Maslin
Typical variant. Photographer: B.R. Maslin
Typical variant. Photographer: B.R. Maslin
Typical variant. Photographer: J. Maslin
, LXT 1183, lab photo by Fiona McCallum ADJUSTED.jpg)
Seed from one herbarium voucher. Scale in mm. Photographer: F. McCallum.
, Habit, BRM 8418, ORIGINAL SCAN, ADJUSTED RICHARD WOODMAN.jpg)
Non-pruinose variant. Photographer: B.R. Maslin
, Stems 1, BRM 8410, ADJUSTED RICHARD WOODMAN.jpg)
Non-pruinose variant. Photographer: B.R. Maslin
, Flowering branch in bud, BRM 8410.jpg)
Non-pruinose variant. Photographer: B.R. Maslin
Botanical name
Acacia glaucocaesia Domin, Biblioth. Bot. 89: 252 (1926)
Description
Erect, somewhat brambly glabrous shrubs or trees 2-4 (-7) m tall, with 1 or 2, much-branched, sub-straight main stems arising from ground level, the crown dense and spreading to about 4 m across. Bark smooth and pruinose on young plants but with age becoming grey and very finely longitudinally fissured towards base of main stems and smooth and pale bronze or pruinose on upper branches (typical variant) or lime green (non-pruinose variant), old wood sometimes twiggy by persistent, defoliated, dead short branchlets. Branchlets pruinose (typical variant) or green (non-pruinose variant). New shoots green. Stipules spiny and slender but generally absent from mature plants (although minute, blunt stipule bases often persisting as tooth-like projections at nodes). Phyllodes mostly elliptic to narrowly elliptic or lanceolate, 13-28 (-35) mm long, (5-) 7-13 (-17) mm wide, 1:w = 1.5-3, thin-textured, glaucous to sub-glaucous and lightly to moderately pruinose (typical variant) or dark green (non-pruinose variant); midrib evident but not prominent; the apex rounded to obtuse. Gland not overly prominent, situated on upper margin of phyllodes 0-1 mm above the pulvinus, small (0.3-0.5 mm long). Inflorescences mostly short racemes (1-6 cm long) with some peduncles subtended by secondary phyllodes, sometimes a few simple and initiated on new shoots as in A. synchronicia , both types may be present on a single plant; peduncles mostly twinned, 7-10 (-13) mm long, slender; heads showy and prolific, globular, lemon yellow or light golden, densely 35-50-flowered. Flowers 5-merous; sepals free. Pods narrowly oblong, flat but rounded over seeds along the midline, 10-40 mm long, 9-13 mm wide, papery, moderately pruinose (typical variant; pods not seen for non-pruinose variant). Seeds transverse in the pods, obloid to ovoid, 4.5-5 mm long, 3-4 mm wide, slightly shiny, brown to black, usually not mottled but sometimes obscurely so; the funicle short, thick, cream and scarcely expanded into an aril.
Characteristic features
Glabrous shrubs or small trees. Bark normally pruinose on stems of young plants and upper branches of mature plants (a rare non-pruinose variant is known). Spiny stipules but usually absent from mature plants. Phyllodes short and broad (mostly 13-28 x 7-13 mm with 1:w = 1.5-3), thin-textured, commonly glaucous to sub-glaucous and lightly to moderately pruinose (typical variant) or dark green (non-pruinose variant), midrib not prominent, apices rounded to obtuse . Gland not overly prominent. Inflorescences mostly short racemes (1-6 cm), sometimes intermixed with a few that are simple (i.e. non-racemose); heads showy and prolific, lemon yellow or light golden, densely 35-50-flowered; peduncles mostly twinned, slender. Pods narrowly oblong, wide (9-13 mm), papery, flat but rounded over seeds along the midline. Seeds transverse in the pods, funicle scarcely expanded into an aril.
Distribution and ecology
Confined to the Pilbara region of northwest Western Australia where it is known from a few scattered localities in the northern and western part of the region, extending from Mardi Station (south of Karratha) to about 80 km east and southeast of Port Hedland. A population from Salt Creek, which is located outside the Pilbara between Port Hedland and Broome, is tentatively referred to this species (see Maslin 1992 for discussion). Acacia glaucocaesia forms rather dense, highly localized, almost pure stands in the areas where it occurs. It grows in sometimes stony, brown clay or clay-loam, in low-undulating hilly country along diffuse drainage lines (e.g. near Cleaverville) and also on alluvial plains of well-defined watercourses such as the Peawah River.
Flowering and fruiting period
Flowering extends from July to October. Pods with mature seeds have been collected in late October and November.
Variation
Non-pruinose forms of this species occur in some populations, usually at a low frequency. They are characterized by lime green stems and branches, and dark green phyllodes.
Taxonomy
Acacia glaucocaesia is a member of the 'A. victoriae group' of species (see Maslin 1992 for discussion); other members of this group that occur in the Pilbara include A. aphanoclada, A. cuspidifolia, A. robeorum, A. synchronicia and A. victoriae.
Affinities
Acacia glaucocaesia is most closely related to A. synchronicia and A. victoriae from which it is most readily distinguished by a combination of its short, broad, thin-textured phyllodes, lemon yellow or light golden heads that are mostly arranged in short racemes and its spiny stipules which are rarely present or more normally completely absent from mature plants. Near Cleaverville (between Karratha and Roebourne) A. glaucocaesia grows with A. synchronicia and some plants in this population appear to represent hybrids between the two but further study is needed to confirm this. Apart from the characters already noted, A. synchronicia can be further distinguished from A. glaucocaesia by its more straggly growth habit and its more open crowns. The phyllodes of A. synchronicia are normally narrower than those found on A. glaucocaesia, however, in the vicinity of Marble Bar (150-250 km east of where A. glaucocaesia occurs) there is a broad phyllode variant of A. synchronicia with pruinose branchlets that superficially resembles A. glaucocaesia, but which is distinguished by its simple (non-racemose) inflorescences, golden heads and thicker, more fleshy phyllodes which possess a prominent basal gland: see A. synchronicia (broad phyllode variant). Acacia glaucocaesia is not known to grow with A. victoriae.
Notes
Acacia glaucocaesia would make an attractive garden plant with masses of lemon yellow to light golden heads and (at least the young plants) white stems. Even the green variant is horticulturally attractive.
Interesting historical coincidences are related to the naming of this species. Acacia glaucocaesia first was described by the European botanist, Carl Domin, in 1926. Domin's description was based on specimens collected between the Ashburton and De Grey Rivers by Dr E.E. Clement and these specimens are now lodged at the herbarium in Prague. Two years later two Australian botanists, J.H. Maiden and W.F. Blakely, described this same species as A. glabriflora, unaware of Domin's name A. glaucocaesia. Coincidentally, Maiden and Blakely also based their name on the same E.E. Clement collection that Domin had used, but the Australians had used duplicate specimens of that set which were lodged at the NSW and Kew herbaria. Furthermore, the species name used by Maiden and Blakely (A. glabriflora) had also been used by Domin in 1926, but for a completely different species which does not occur in the Pilbara.
Conservation status
Acacia glaucocaesia is classified as a Priority 3 species on the Department of Environment and Conservation's Declared Rare and Priority Flora List.
Origin of name
The botanical name is derived from the Latin glaucus (blue-green, covered with a white bloom) and caesius (bluish-grey) referring to the appearance of the phyllodes.
References
Domin, K. (1926). Acacia. Bibliotheca Botanica 89: 249-276.
Maslin, B.R. (1992). Acacia Miscellany 6. A review of Acacia victoriae and related species (Leguminosae: Mimosoideae: Section Phyllodineae). Nuytsia 8: 285-309.