Malaccotristicha C.Cusset & G.Cusset

Scientific Description

Family Podostemaceae.

Sometimes included in Tristicha.

Habit and leaf form. Aquatic herbs. Plants of very peculiar form; thalloid (the plants moss-like). Leaves well developed (but minute, on secondary shoots, without axillary buds). Plants with roots (creeping over the substrate and bearing ‘haptera’ or holdfasts that attach the plant; roots with a root cap); unarmed. Annual, or perennial; to up to 0.07 m high. Hydrophytic; rooted (attached to rocks by expanded haustoria). Leaves submerged. Heterophyllous (leaves of different ranks along stem differing in width). Leaves minute; alternate, or whorled (or pseudo-whorled); spiral, or tristichous; 3 per whorl; decurrent on the stems; ‘herbaceous’; imbricate; sessile; non-sheathing; simple. Leaf blades entire; flat; ovate, or triangular; decurrent. Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves without stipules. Leaf blade margins entire; flat. Leaf anatomy. Hairs absent. Stem anatomy. Secondary thickening absent (vascular tissue greatly reduced).

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

Inflorescence and flower features. Flowers solitary; terminal, or axillary (borne on various parts of the plant from near the roots to near tips of shoots; each flower with usually two short leafy shoots growing beside it); pedicellate; bracteolate. Bracteoles persistent. Bracteoles not adnate to the receptacle. Flowers minute; regular; 3 merous; cyclic; tricyclic. Free hypanthium absent. Hypogynous disk absent. Perianth sepaline; 3; 1 -whorled; joined. Calyx present; 3; 1 -whorled; polysepalous (not in Australian species), or gamosepalous (shortly to extensively connate, segments ellipsoid). Calyx lobes markedly shorter than the tube, or about the same length as the tube. Calyx erect; glabrous; regular; membranous; non-fleshy; persistent. Corolla absent. Androecium present. Androecial members definite in number. Androecium 1–3 (usually 2 in Western Australia). Androecial members free of the perianth; all equal; free of one another; 1–3 -whorled. Androecium exclusively of fertile stamens. Stamens (1–)2–3; all more or less similar in shape; reduced in number relative to the adjacent perianth to isomerous with the perianth; alternisepalous. Filaments glabrous. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen shed in aggregates, or shed as single grains; if aggregated, in diads. Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; synovarious to synstylovarious; superior. Ovary plurilocular; 3 locular. Gynoecium non-stylate. Stigmas 3; entire or laciniate. Placentation axile. Ovules 2–50 per locule ("numerous"); anatropous.

Fruit and seed features. Fruit non-fleshy; not hairy; dehiscent; a capsule; 3 celled; 3 locular. Dispersal unit the seed. Fruit 2–100 seeded. Seeds non-endospermic (there being no double fertilization); small. Cotyledons 2. Embryo straight.

Geography, cytology, number of species. World distribution: southeast Asia (Malaysia, Thailand) and northern Australia. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia and Northern Territory. Northern Botanical Province. A genus of 3 species; 1 species in Western Australia; 0 endemic to Western Australia.

Additional characters Occurrence of root cap; presence of short accessory shoots beside flower; stamens usually 2.

Etymology. From the Greek or Latin for "three" and "a row or line", in reference to the arrangement of the leaves in three rows down the stem.