Families of Flowering Plants of Australia

Podostemaceae

This small, specialised family is almost pantropical and most diverse in Central and South America and Asia, always growing on stones in fast-flowing rivers. The two genera in Australia (Torrenticola and Tristicha) are only found in clear-water streams in northern Australia.

Characteristic features of the family Podostemaceae in Australia include:

peculiar moss-like plants, with thallose or ribbon-like roots attached to rocks, and short stems with overlapping leaves
flowers inconspicuous, enclosed by spathe-like bracts when young, giving the appearance of moss capsules

Description

Annual or perennial aquatic herbs rooted in the substrate with their leaves all or mostly submerged. Perennating by rhizomes. Vegetative reproduction by rhizomes. Plants sometimes lacking recognisable stems or leaves. Internal secretions not obvious. Plants glabrous. Leaves well developed or much reduced (i.e. to scales, etc.), alternate and spiral, or distichous, or in whorls of 3, cauline, sessile. Stipules absent. Lamina simple, symmetric, filiform, acicular, subulate, linear, lanceolate, ovate or oblong; base truncate; margins entire, dentate or serrate, ±flat, revolute, recurved, involute or incurved; one-veined, or the venation not obvious, with the midrib inconspicuous, and the tertiary venation not reticulate; surfaces not punctate; herbaceous. All the flowers bisexual. Inflorescences terminal, consisting of dichasial or monochasial cymes or solitary flowers. Spathes present. Bracts present. Bracteoles present or absent. Flowers odourless, sessile or stalked. Perianth regular, of 1 whorl only, with 1–3, free or fused, sepaloid segments, valvate in bud, urn-shaped, green, herbaceous. Fertile stamens 1–3, alternating with and free of the perianth segments, free of the ovary and style, distinct from each other, all ±equal. Anthers basifixed, not versatile, opening inwards by longitudinal slits, 2-celled. Ovary superior and sessile. Carpels 2–3, fused; ovary with 2–3 locules. Style branching from the base, or absent and the stigma ±sessile on the ovary. Ovules 2–numerous per locule, stalked; placentation axile. Fruit a dry, dehiscent septicidal capsule; the perianth on the maturing fruit deciduous or dry and persistent. Disseminule micro-surface ±smooth or papillate, orange or brown, dull. Seeds 2–numerous per fruit. Aril absent. Cotyledons 2. Embryo straight.
(Note: this description has been generated from the coded data compiled for the key. Any errors in the key data will be reflected in the descriptions.)

A treatment of the family Podostemaceae has been published in:
Flora of Australia 18: 15.

Australian genera of Podostemaceae (as recognised for the Flora of Australia)

Torrenticola
Tristicha