Arenaria L.

Scientific Description

Family Caryophyllaceae.

Subfamily Alsinoideae, Tribe Alsineae.

Habit and leaf form. Herbs, or shrubs (rarely, subshrubs); non-laticiferous and without coloured juice. ‘Normal’ plants. Leaves well developed. Plants with roots; non-succulent; unarmed. Annual, or biennial, or perennial. Leaves basal (tufted), or basal and cauline. To 0.5 m high. Self supporting (or cushion-forming). Mesophytic. Not heterophyllous. Leaves variable small to very large; not fasciculate; opposite; with blades; sessile; simple; not peltate. Leaf blades entire; flat; very variable. Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves without stipules. Leaf blade margins entire; flat. Leaf anatomy. Hairs absent; glandular hairs absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries absent.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’, or solitary. Inflorescence few-flowered. Flowers in cymes. Inflorescences compound. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary (rarely). Flowers pedicellate; small; regular; tetracyclic, or tricyclic (rarely). Free hypanthium present (shortly perigynous). Perianth with distinct calyx and corolla, or sepaline (rarely); 10, or (4–)5 (rarely); 2 -whorled, or 1 -whorled (rarely); isomerous, or anisomerous (rarely). Calyx present; (4–)5; 1 -whorled; polysepalous; glabrous; valvate. Corolla present, or absent; 0, or 5; 0 -whorled, or 1 -whorled; polypetalous; contorted, or imbricate (rarely); white, or pink (rarely), or purple (rarely). Petals emarginate or bifid; sessile. Corolla members entire. Androecium present. Fertile stamens present. Androecium 8–10. Androecial members all equal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens. Stamens 8–10; diplostemonous. Anthers separate from one another; dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Fertile gynoecium present. Gynoecium 1 carpelled. The pistil 1 celled. Gynoecium syncarpous; synovarious; superior. Ovary unilocular; 1 locular. Gynoecium stylate. Styles (2–)5; free; simple. Stigmas (2–)5; 1 - lobed. Placentation free central, or basal. Ovules campylotropous.

Fruit and seed features. Fruit ca 7 mm long; not hairy; dehiscent; a capsule. Dispersal unit the seed. Fruit several. Perisperm present. Seeds minute.

Geography, cytology, number of species. Holarctic. Adventive. Not endemic to Australia. Australian states and territories: Western Australia, South Australia, Queensland, New South Wales, Victoria, and Tasmania. South-West Botanical Province. 2n=16, 18, 20, 22, 24, 26, 28, 30, 36, 40, 44, 46, 80, 100, 120, ca 200, 240. A genus of ca 150 species; 1 species in Western Australia; 0 endemic to Western Australia.