Sclerolaena is a genus of flowering plants in the family Amaranthaceae (order Caryophyllales), encompassing approximately 78 accepted species of annuals and short-lived perennial herbs. The genus is endemic to Australia, where species are widespread across arid and semi-arid regions.
Plants are typically divaricately branching, woody herbs with alternate leaves that may be terete, semiterete, or flattened. Flowers are axillary, usually solitary and mostly bisexual, with five stamens and two styles. The most diagnostic feature of the genus is the fruiting perianth: it becomes thickened and hardened at maturity and bears spines arranged alternately to the perianth segments, with a characteristic pair of spines opposite the radicular bulge. The number, size, and arrangement of these spines — ranging from two to six or more per fruit, and varying from erect and parallel to spreading or recurved — is the primary character used to distinguish species.
As the fruit ripens, the hardened perianth either disarticulates readily or remains attached to the branch, allowing the whole plant or a section of it to be wind-dispersed as a tumbleweed-like unit. The upper portion of the perianth often remains distinct and is termed the "limb." Seeds are released by the eventual breakdown of the woody perianth.
Sclerolaena belongs to Chenopodiaceae in many treatments, a family now subsumed within the broader Amaranthaceae under the APG system. The genus includes species such as Sclerolaena muricata (spiny burr-grass), Sclerolaena bicornis, and Sclerolaena divaricata, which are familiar components of semi-arid Australian shrublands and grasslands.
Distribution
Sclerolaena is endemic to Australia, with species occurring across arid and semi-arid regions of the continent. The genus is well represented in New South Wales and extends throughout inland Australia wherever dry shrublands and grasslands occur.
Ecology
Species of Sclerolaena are characteristic of arid and semi-arid Australian habitats, including dry grasslands, shrublands, and chenopod plains. The hardened, spiny fruiting perianth facilitates dispersal: in some species the entire plant or a branch breaks off and is tumbled by wind, carrying the enclosed seeds across open terrain.
Taxonomy Notes
Sclerolaena was traditionally placed in Chenopodiaceae, a family now incorporated into the expanded Amaranthaceae sensu lato under the APG classification system. It sits within the order Caryophyllales. GBIF currently lists the family as Chenopodiaceae; Wikipedia's article uses Amaranthaceae — both names refer to the same circumscribed group.
