Potamogetonaceae

This is a small but cosmopolitan family, found almost anywhere its habitat of permanent, still or flowing, fresh or slightly brackish waterbodies are found. Similarly, in Australia it can be found anywhere there is suitable habitat, including Central Australia.

Characteristic features of the family Potamogetonaceae in Australia include:

• aquatic herbs with alternate leaves which may be all submerged and similar in shape (usually linear), or with some submerged and others floating, the latter usually ovate or elliptical and prominently parallel-veined; all leaves have a conspicuous sheathing base
  
• flowers small, borne in dense spikes, bisexual, with 4 rather thick, greenish perianth parts and 4 sessile anthers
  
• ovary superior, comprising 4 more or less free carpels with style short or absent, each carpel developing into a small drupe-like fruit

Description

Annual or perennial aquatic herbs rooted in the substrate with their leaves all or mostly submerged or floating. Perennating by rhizomes or turions (a short, condensed shoot, filled with starch). Vegetative reproduction by rhizomes, stolons or turions. Stem internodes terete, or oval, or slightly flattened. Internal secretions not obvious. Plants glabrous. Leaves alternate and spiral, or distichous, or rarely apparently opposite, apparently petiolate or sessile. Stipule-like lobes absent, or the ligule often stipule-like and ochreate or intrapetiolar, scale-like, membranous, bristle-like, lacerate or fimbriate. Lamina simple, symmetric, filiform, acicular, subulate, linear, lanceolate, ovate, elliptic, oblong or orbicular; base attenuate, rounded, lobed or auriculate; margins entire or serrate, ±flat or undulate; venation parallel with the midrib, conspicuous, and the tertiary venation reticulate or not reticulate; surfaces not punctate; herbaceous, membranous or papery. Leaf ligule present, rarely absent. All the flowers bisexual. Inflorescences axillary, consisting of spikes. Spathes rarely present. Bracts present or absent. Pollination by wind, water or possibly by insects. Flowers odourless, sessile. Perianth regular, of 1 whorl only, with 4 free sepaloid segments, valvate in bud, green, without contrasting markings, herbaceous or papery, sometimes comprised of scales; base clawed. Fertile stamens 4, alternating with and free of or at least partly fused to the perianth segments, free of the ovary and style, distinct from each other, all ±equal. Staminodes absent, or apparently present. Anthers basifixed, not versatile, opening outwards by longitudinal slits, 2-celled. Ovary superior and sessile. Carpels 4, free from each other. Style terminal, single and unbranched. Ovules 1 per carpel, ±stalked; placentation marginal. Fruit a dry or fleshy indehiscent drupelet; the perianth on the maturing fruit deciduous. Disseminule micro-surface ±smooth, costellate, colliculate, tuberculate, verrucose or rugose, green or brown, dull. Seeds 1 per fruit. Aril absent. Cotyledons 1. Embryo curved.
(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 Potamogetonaceae has not yet been published in the Flora of Australia. It will appear in Volume 39.

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

† = some species native, others introduced

†Potamogeton

Potamogeton tricarinatus (flowering plant)
Photo: M.Fagg © ANBG