Subfamily Paronychioideae, Tribe Polycarpeae. The genus is closely related to Spergularia. Pedersen (1984) suggests that both genera should be combined.
Habit and leaf form. Herbs; non-laticiferous and without coloured juice. ‘Normal’ plants. Leaves well developed. Plants with roots. Annual, or perennial (rarely). Leaves cauline. To 0.1–0.3 m high. Self supporting. Mesophytic. Not heterophyllous. Leaves fasciculate (often); opposite, or whorled (apparently); with blades; fleshy; sessile; not connate; simple; not peltate. Leaf blades entire; linear. Mature leaf blades adaxially sparsely glandular pubescent; abaxially sparsely glandular pubescent. Leaves with stipules (4 per leaf pair). Stipules free of one another; scaly (‘scarious’); caducous. Leaf blade margins entire. Leaf anatomy. Hairs present; glandular hairs present.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the disk.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes. Inflorescences compound. The terminal inflorescence unit cymose. Inflorescences terminal; without involucral bracts. Flowers pedicellate; small; regular; tetracyclic, or tricyclic (rarely). Free hypanthium present (‘subperigynous’). Perianth with distinct calyx and corolla, or sepaline (rarely); 10, or 5 (rarely); 2 -whorled, or 1 -whorled (rarely); isomerous. Calyx present; 5; 1 -whorled; polysepalous; imbricate, or valvate (rarely). Corolla present, or vestigial (rarely), or absent (rarely); 0, or 5; 0 -whorled, or 1 -whorled; polypetalous; contorted, or imbricate (rarely); white. Petals oblong to obovate; sessile. Corolla members entire. Androecium present. Fertile stamens present. Androecium 5–10. Androecial members markedly unequal (when stamens 10, the episepalous stamens longer), or all equal; free of one another (inserted on the glandular disk); 1 -whorled, or 2 -whorled. Androecium exclusively of fertile stamens. Stamens 5–10; isomerous with the perianth, or diplostemonous (obdiplostemonous); oppositisepalous (whether stamens 10 or 5). Anthers separate from one another; dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Fertile gynoecium present. Gynoecium 3 carpelled, or 5 carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary unilocular; 1 locular. Gynoecium stylate. Styles 3, or 5; partially joined; simple. Stigmas 3 - lobed, or 5 - lobed. Placentation free central, or basal. Ovules campylotropous.
Fruit and seed features. Fruit 4–6 mm long; dehiscent; a capsule. Capsules valvular. Dispersal unit the seed. Fruit 50 seeded (‘numerous’). Perisperm present. Seeds small, or minute.
Geography, cytology, number of species. Holarctic. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. 2n=18. A genus of 6 species; 2 species in Western Australia; S. arvensis L., S. pentandra L.; 0 endemic to Western Australia.
Additional comments. Spergula arvensis is occasionally used for forage and green manure (Bittrich 1993:217).
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/