Families of Flowering Plants of Australia

Aponogetonaceae

This is a small family distributed from South Africa, through India to China and south into northern and north-eastern Australia where it is represented only by the genus Aponogeton, all species of which are freshwater aquatics. In addition to the native species, the South African A. distachyos is naturalised and is sometimes found in temperate waterbodies.

Characteristic features of the family Aponogetonaceae in Australia include:

aquatic plants, mostly of permanent or semipermanent, still water
adult leaves long-stalked, usually with floating, elliptic blades with parallel veins and fine interveins at right angles to the main veins
flowers coloured or white, borne in dense spikes surrounded at the base by a sheath
perianth small and inconspicuous
ovary superior, of 2-9 free carpels, developing into leathery follicles in fruit

Description

Perennial aquatic herbs, rooted in the substrate with their leaves all or mostly submerged or floating, perennating by tubers. Vegetative reproduction absent or by detached stem parts, rarely by tubers. Internal secretions not obvious. Plants glabrous. Leaves well developed or much reduced (i.e. to scales, etc.), alternate and spiral, all or mostly basal, petiolate. Stipule-like lobes absent. Lamina simple, symmetric, filiform, acicular, subulate, linear, lanceolate, ovate or elliptic; base attenuate, rounded or cordate; margins entire, ±flat, revolute, recurved, involute or incurved; venation parallel, with the midrib conspicuous or inconspicuous, and the tertiary venation reticulate or not; surfaces not punctate; herbaceous, membranous or papery. Leaf ligule absent. Plants with all the flowers bisexual. Inflorescences axillary, consisting of spikes. Spathes present or absent. Bracts present or absent. Flowers odourless or fragrant; sessile. Floral disc absent; nectaries apparently absent or on the carpels. Perianth regular or irregular, of 1 whorl only, with 1, 2 or 6, free, sepaloid or petaloid segments, or vestigial or absent, imbricate in bud; white, yellow, pink or green, without contrasting markings, membranous; lobes ±entire. Fertile stamens 6–numerous, not clearly correlated with and free of the perianth, free of the ovary and style, distinct from each other, all ±equal. Anthers basifixed, not versatile, opening sideways by longitudinal slits; 2-celled. Ovary superior and sessile. Carpels (2–) 3 (–6), free. Style terminal or eccentric, single and unbranched. Ovules 2–12 per locule, stalked or apparently sessile; placentation basal. Fruit a dry or somewhat fleshy, dehiscent follicle. Disseminule micro-surface ±smooth, ridged or reticulate, brown, grey or black, glossy or dull. Seeds 1 (–4) per fruit. Aril absent. Cotyledons 1. 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 Aponogetonaceae has not yet been published in the Flora of Australia. It will appear in Volume 39.

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

† = some species native, others introduced

†Aponogeton