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Zosteraceae


This is a small family of seagrasses from mainly subtropical and temperate seacoasts of both hemispheres. In Australia it occurs around the southern and eastern shorelines.

Characteristic features of the family Zosteraceae in Australia include:

  • perennial seagrasses often forming extensive beds with 2-ranked alternate, thin, linear leaves, edgewise to the stems with sheathing bases, and often truncate tips
  • flowers small, unisexual, borne in 2 rows on a flattened axis which is enclosed in an upper leaf sheath
  • female flower comprising a naked carpel, male flower a single stamen
  • fruit indehiscent, dry, 1-seeded

Description

Annual or perennial marine aquatic herbs rooted in the substrate with their leaves all or mostly submerged. Perennating by rhizomes. Vegetative reproduction by rhizomes. Internal secretions not obvious. Plants glabrous. Leaves distichous; both basal and cauline, subsessile. Stipule-like lobes present or apparently absent. Lamina simple, symmetric, filiform, acicular, subulate or linear; base lobed or auriculate; margins entire, ±flat; venation parallel, with the midrib conspicuous, and tertiary venation not reticulate; surfaces not punctate; herbaceous. Leaf ligule present. Male and female flowers occurring on the same plant. Inflorescences axillary, consisting of spadices. Spathes present. Bracts present. Pollination by water. Flowers odourless, sessile or stalked. Floral disc absent; nectaries absent. Perianth absent. Fertile stamens 2, free from ovary, distinct from each other, all ±equal. Staminal filaments absent. Anthers not versatile, opening outwards by longitudinal slits, 2-celled. Ovary sessile. Carpel 1; ovary with 1 locule. Style terminal, branching from the base. Ovule 1, sessile; placentation apical. Fruit dry or fleshy, indehiscent or tardily dehiscent; drupe-like or with irregular dehiscence (camara). Disseminule macro-surface featureless or awned; micro-surface ±reticulate, black, glossy or dull. Seed 1 per fruit. Aril absent. Cotyledons 1. Embryo sharply bent.
(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 Zosteraceae has not yet been published in the Flora of Australia. It will appear in Volume 39.

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

Heterozostera
Zostera


Heterozostera tasmanica (habit)
Photo: S.Jacobs S.Jacobs 


Zostera muelleri (beach-washed plants)
Photo: K.Thiele K.Thiele 


Zostera muelleri (flowering plant)
Photo: K.Thiele K.Thiele 


Zostera muelleri (flowers and fruits)
Photo: K.Thiele K.Thiele