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Hydatellaceae


This is a very small family endemic to Australia except one species of Hydatella which occurs in New Zealand. Members of the family grow in the mud of seasonally drying, freshwater pools and along streambanks, mostly in south-western Australia but with one species scattered across much of southern Australia, one scattered across northern Australia and one in the highlands of Tasmania.

Characteristic features of the family Hydatellaceae in Australia include:

  • tiny, annual or perennial, tufted, sedge-like herbs
  • leaves all basal, linear or thread-like, without distinct sheaths
  • flowers minute, unisexual, clustered together into small, terminal heads surrounded by spreading bracts, without a perianth, the males comprising a single stamen, the females a solitary carpel
  • fruits membranous, splitting at maturity or not

Description

Annual or perennial terrestrial herbs, or aquatic herbs rooted in the substrate with their leaves submerged or emergent. Perennating by rhizomes. Internal secretions not obvious. Plants glabrous, or with simple, non-glandular, uniseriate hairs. Leaves alternate and spiral, all or mostly basal, sessile. Stipule-like lobes absent. Lamina simple, symmetric, filiform, acicular, subulate or linear; margins entire; base ±truncate, ±flat; one-veined, with the midrib inconspicuous, and the tertiary venation not reticulate; surfaces not punctate; herbaceous. Leaf ligule absent. Male and female flowers occurring on the same plant or on separate plants, or with all the flowers bisexual. Inflorescences terminal, consisting of capitula or solitary flowers. Bracts present. Pollination by wind. Flowers odourless; sessile. Floral disc absent; nectaries absent. Perianth absent. Fertile stamens 1, free of the ovary and style. Anthers basifixed, not versatile, opening sideways by longitudinal slits, 2-celled. Ovary superior and sessile. Carpel 1; ovary with 1 locule. Style absent and the stigma ±sessile. Ovule 1, stalked; placentation apical. Fruit dry, dehiscent or indehiscent, a capsule with irregular or valvular dehiscence, or an utricle. Disseminule micro-surface ±smooth, alveolate or reticulate, cream or brown, dull. Seeds 1 per fruit. Aril absent. Cotyledons 1. Embryo round or shapeless.
(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 Hydatellaceae has been published in:
Flora of Australia 45: 15.

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

Hydatella
Trithuria


Hydatella australis
 


Trithuria submersa