Cypress-pine (Silba 1986).
A genus of three species:
Gadek and Quinn (1993) assigned Actinostrobus to the subfamily Actinostrobus, along with Diselma, Callitris and Widdringtonia. See Callitris for a discussion of the close but ambiguous relationships between Actinostrobus, Callitris and Neocallitropsis. Some taxonomists have chosen to use these studies to submerge Actinostrobus within Callitris, but I find that such a judgement, primarily demonstrated through a single study with ambiguous findings, is premature.
Type species: Actinostrobus pyramidalis Miquel. A. acuminatus, described in 1864, differs in having solitary cones, retaining juvenile foliage in the adult plant (a primitive character in Callitris), and in having a different growth habit. A. arenarius, described in 1964, is almost identical to A. pyramidalis except for the minor difference in cone shape described below. Accordingly A. acuminatus appears to be phylogenetically basal to the other two species (Farjon 2005).
"Monoecious shrubs with jointed branchlets. Buds inconspicuous. Juvenile leaves needle-like, 3-ranked. Mature leaves scale-like, small, in whorls of three, acutely pointed, sometimes with sparse resin spots, without prominent stomata. Male cones oblong or somewhat globular with stamens in whorls of 3-6 vertical columns. Female cones borne erect, ripening the first year, ovoid to globose; with six triangular, grooved, somewhat overlapping scale on a central axis; each scale bearing 1-2 triangular, 3-winged seeds; cone opens in the center upon maturity; the base of the cone surrounded by closely pressed, rounded bracts. Seeds tan, with even wings; seeds emit a yellowish dye if crushed. Cotyledons 2" (Silba 1986). Chromosomes 2n = 22, which is usual in Cupressaceae (Farjon 2005).
|1||Both juvenile (acicular) and adult (scale-like) leaves present on mature plant; seed cones usually solitary, 1.5 times as long as broad; tips of scales hooked||A. acuminatus|
|+||Leaves on mature plants scale-like, seed cones clustered on stems||2|
|2||Apex of female cone rounded; scales with incurved, obtuse apex||A. pyramidalis|
|+||Female cone as long as broad; scales not incurved, with acute apex||A. arenarius|
Western Australia, with all three species confined to a relatively small part of southwest Australia. A. pyramidalis and A. arenarius are commonly found with one other conifer, Callitris preissii (Farjon 2005).
Actinostrobus and Callitris constitute Australia's only arid region conifer genera, and it this sense they represent ecological analogues of the relatively unrelated northern hemisphere Juniperus. All three genera are, for the most part, scale-leaved shrubs and small trees that form dominant cover types in warm semiarid and arid environments.
Miquel, F.A.G. 1845. Cupressinae Richard. V.1, p.643-645 in J.G.C. Lehmann, Plantae Preissianae. Hamburg.
Piggin, J., and J.J. Bruhl. 2010. Phylogeny reconstruction of Callitris Vent. (Cupressaceae) and its allies leads to inclusion of Actinostrobus within Callitris. Australian Systematic Botany 23:69-93.
Baker, R.T. and H.G. Smith. 1910. A research on the pines of Australia. NSW Technical Education Series No. 16. Sydney. (p.290-298).
Farjon (2005) provides a detailed account, with illustrations.
Last Modified 2012-11-23