Caustis is a genus of rhizomatous perennial sedges in the family Cyperaceae (order Poales), endemic to Australia. The genus comprises about seven species found across all Australian states except the Northern Territory. Plants have terete (cylindrical) culms that are often bulbously thickened at the base, with leaves reduced to sheaths along and at the base of the culm — a morphological adaptation typical of dry-adapted or nutrient-poor-habitat sedges. The inflorescence is as long as or longer than the culms, with numerous grooved to flattened branches that elongate with maturity. Flowering is unusual within Cyperaceae: spikelets contain one bisexual or female flower, often with a male flower below, and inflorescences can be functionally unisexual, sometimes with male- and female-appearing inflorescences arising side by side on the same rhizome. Glumes number 3–6 and are spirally arranged; the perianth is absent. Stamens range from 3 to 6, and the style is 3- to 5-fid with a persistent, thick, narrow-conical to pyramidal style base that is hispid at the apex and smooth below. The nut is trigonous to terete, readily deciduous, glabrous, and features a narrow elongated neck between the body of the nut and the style base. Notable species include the Curly Wig (Caustis flexuosa), named for its strongly curled to flexuous inflorescence branches, and Caustis recurvata with similarly curled branches but differing stamen count and sterile branchlet distribution.
Distribution
Caustis is endemic to Australia, occurring in all Australian states except the Northern Territory. The genus comprises about seven species, found across temperate and subtropical regions of the continent from Queensland and New South Wales to Western Australia.
Taxonomy
Caustis belongs to the sedge family Cyperaceae within the order Poales. The genus is notable for its variable reproductive biology: functionally male and female inflorescences can appear on culms arising side by side from the same rhizome, and the distribution of male and female flowers and spikelets varies greatly even within a single plant. As noted by K. L. Wilson in the NSW Flora treatment, the life cycle of these plants remains poorly understood and needs further study. Seven descendant species are recorded in GBIF.
