Trianthema L.

Sp.Pl. 2:223 (1753)
Name Status

Scientific Description

Common name. Pigweeds. Family Aizoaceae.

Habit and leaf form. Prostrate or diffuse herbs (stems sometimes woody at the base). Plants succulent. Annual, or perennial. Leaves cauline. Plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Young stems cylindrical. Stem internodes solid. Xerophytic. Leaves minute to medium-sized; opposite (the members of a pair markedly unequal); fleshy; imbricate to not imbricate; petiolate (petioles dilated at base); simple; epulvinate. Leaf blades entire; flat, or solid; linear; one-veined, or pinnately veined, or palmately veined. Leaves with stipules (C), or without stipules. Stipules when present, interpetiolar. Leaf blade margins entire. Vegetative buds not scaly. Leaves without a persistent basal meristem. Leaf anatomy. Hairs present, or absent (or papillose). Urticating hairs absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous (diurnal).

Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; (when flowers aggregated) in cymes, or in fascicles. The terminal inflorescence unit (when flowers aggregated) cymose. Inflorescences axillary; cymes and fascicles. Flowers pedicellate, or sessile; bracteate (each flower subtended by one or more scarious bracts); bracteolate (somewhat scarious); small, or medium-sized; regular; cyclic; tricyclic to polycyclic. Free hypanthium present; incorporating calyx and stamens. Perianth sepaline (considered apetalous, but the calyx coloured inside); 5; 1 -whorled. Calyx present; 5; 1 -whorled; gamosepalous; more or less deeply blunt-lobed; coloured inside; fleshy; persistent. Calyx lobes sometimes unequal, sometimes with dorsal mucro behind apex. Corolla absent. Androecial members definite in number, or indefinite in number. Androecium 5–100. Androecial members branched, or unbranched. Androecial sequence determinable, or not determinable. Androecial members when branched/many, maturing centrifugally; free of the perianth (B), or adnate (AK); all equal; free of one another; 1–16 -whorled (? — to ‘many whorls’). Androecium including staminodes (i.e. without staminodal ‘petals’). Stamens 5–100 (5 to many); all more or less similar in shape; reduced in number relative to the adjacent perianth to polystemonous; when five, alternisepalous (alternating with the calyx lobes); filantherous. Anthers dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen shed as single grains. Gynoecium 1 carpelled (? — pseudomonomerous), or 2 carpelled. The pistil 1 celled, or 2 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary unilocular, or plurilocular; 1 locular, or 2 locular; sessile. Gynoecium stylate. Styles 1 (or 2); apical, or lateral (or excentric). Stigmas 1. Placentation parietal. Ovules in the single cavity 2–50 (to many); anatropous, or campylotropous.

Fruit and seed features. Fruit non-fleshy; dehiscent (circumcision usually near base); a capsule. Capsules circumscissile. Fruit 1 celled; 1–100 seeded (to many). Seeds non-endospermic. Perisperm present (mealy). Embryo well differentiated. Cotyledons 2. Embryo curved.

Etymology. The flowers sometimes grow in threes.

J. Gathe and Leslie Watson, 8 September 2016

Taxonomic Literature

  • Wheeler, J. R.; Rye, B. L.; Koch, B. L.; Wilson, A. J. G.; Western Australian Herbarium (1992). Flora of the Kimberley region. Western Australian Herbarium. Como, W.A.
  • Blackall, William E.; Grieve, Brian J. (1988). How to know Western Australian wildflowers : a key to the flora of the extratropical regions of Western Australia. Part I : Dicotyledons (Casuarinaceae to Chenopodiaceae). University of W.A. Press. [Perth].
  • Australia. Bureau of Flora and Fauna (1984). Flora of Australia. Volume 4, Phytolaccaceae to Chenopodiaceae. Australian Govt. Pub. Service. Canberra.