Corkwoods, Corkbark

Trees, rarely shrubs, with thick corky bark. Leaves simple or compound, terete or flat, not conspicuously petiolate, not stem-clasping, entire, rarely grooved below; marginal veins and midrib visible. Inflorescence axillary, 1-few long racemes, sometimes arising from older leafless axils, not resprouting in subsequent years; bud involucre tiny; rachis 9-250 mm long. Flowers 25-120 per raceme; pedicel pubescent, rarely glabrous. Perianth curved or rarely almost straight in bud, splitting to base into 4 distinct tepals, pubescent. Pistil 8.5-33 mm long; pollen presenter oblique disc, rarely conical on oblique basal flange; gland prominently U-shaped. Fruits many, pointing upwards on pendent rachis, varyingly retained on plant, not markedly woody, smooth, prominently to obscurely beaked, horned, dehiscing fully down both sides. Seed occupying part or most of valve; wing terminal only, or decurrent up to c. halfway down one side of seed body, not at all down other.

A group of nine species found in all mainland States except Vic., mostly in arid and subtropical areas.

This treatment retains a traditional view of the species making up this distinctive group in the genus, with the exception of the application of the name H. fraseri to an unusual species occupying a restricted ridgetop habitat in the northern tablelands of N.S.W., and the treatment of H. lorea and its allies with long leaves and densely pubescent or tomentose inflorescences and branchlets. Three species formerly segregated from H. lorea have been recombined with that species, since they are mostly distinguished from each other by few characters which often overlap in variation. This variation may occur within populations or in a geographical intergrade zone. Simple erect hairs, sometimes 'crisped', occur quite often in the inflorescence and rarely extend onto the current season's branchlets. They have been referred to as 'glandular hairs' though they may in all species inconsistently bear the gland tips. The lack of a gland tip seems to reflect deciduousness of a gland in some cases (the hair tip is truncated, possibly caused by drying out) or a phenotypic variation, as on any given plant the simple hairs may vary in the possession of the gland. The corkwoods are the only group of Hakea which possess these hairs. Corkwood species are distinctive in the arid and subtropical regions for their gnarled fissured stems, strap-like or divided leaves, long showy nectariferous cream or yellow inflorescences often visited by honeyeaters and conspicuous infructescences. The perianth base is dark-coloured from the large purple-black gland within. The taxonomy of this group of species is particularly difficult compared with most of Hakea . While it is clear there are a number of species, the many characters varying across the group do so in parallel in a number of species. Apart from the porrect pollen presenter of H. ednieana , there are no unique diagnostic characters. The taxonomy, therefore, has been based on a knowledge of population and regional variation. Completely glabrous plants or ones just possessing glandular hairs in the infloresence may occur rarely in a number of species other than H. chordophylla , namely H. lorea , H. divaricata and H. eyreana . They have been given formal names at a varietal or form level in the past, but there is no real benefit in maintaining these as it is likely, from limited observation, that they do not occur as separate populations. Similarly, while most species have leaves typically either simple or compound, in most species there may be variation between plants or even on an individual plant. One or other variation is usually rare in most of the species, but is more common in H. ivoryi and H. pulvinifera .

Data derived from Flora of Australia Volumes 16 (1995), 17A (2000) and 17B (1999), products of ABRS, ©Commonwealth of Australia