Electronic Flora of South Australia Genus Fact Sheet
Phylum Magnoliophyta – Subphylum Seagrasses – Class Liliopsida – Subclass Alismatidae – Order Potamogetonales – Family Zosteraceae
Monoecious; perennials with monopodial]y branched herbaceous rhizomes. Rhizomes with internodes in transverse section showing only 2 lateral vascular bundles in the cortex, one either side of the central vascular strand. Roots 2 per node, or arising in two groups of 1-several roots at each node. Vegetative shoots very short, bearing 2–6 leaves and arising laterally from the nodes. Leaves alternate, distichous; sheath open (in southern Australian species of subgenus Zosterella), margins overlapping, ligulate, auriculate; blade linear, deciduous, leaving a senescent sheath; apex variable in shape. Squamules in pairs (in southern Australian species). Fertile shoots simple or sympodially branched; spathes stalked, resembling vegetative leaves, sometimes somewhat inflated, enclosing the spadices. Male and female flowers arranged alternately in 2 longitudinal rows on the spadix; retinacules present (in southern Australian species), usually one near each male flower. Seed ovoid to ellipsoid, longitudinally striate and with numerous finer transverse striations.
Type species: Z. marina Linnaeus.
Taxonomic notes: There are about 12 species widely distributed in temperate regions of both hemispheres. Three species occur in southern Australia, generally in intertidal regions on soft substrates.
All southern Australian Zostera species belong to the subgenus Zosterella which is characterised by having an open leaf sheath, and retinacules present on the spadices.
Pollination in Zostera is always hydrophilous and usually takes place below the water surface. However pollination on the water surface has been recorded (e.g. den Hartog 1970, p. 12) with intertidal populations where pollen drifts to the partially exposed stigmas.
* The shape of the leaf apex is a useful diagnostic character especially in juvenile leaves. It should be assessed from the whole plant and not from only one or two leaves and should be used in conjunction with other characters.
DEN HARTOG, C. (1970). The seagrasses of the World. Verh. k. ned. Akad. Wet. Afd. Natuurk., ser. 2, 59(1), 1–275 (-1–31 Plates).
LINNAEUS, C. (1753). Species Plantarum. Vols 1, 2. (Laurenti Salvii: Stockholm.)
The Marine Benthic Flora of Southern Australia Part I complete list of references.
Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
©Board of the Botanic Gardens and State Herbarium, Government of South Australia
KEY TO SPECIES OF ZOSTERA
1. Leaf apex* more or less tridentate, with the central vein ending in a distinct mucro; roots two only at each node
1. Leaf apex truncate, or rounded and notched, the central vein without a mucro; roots two to several at each node
2. Leaf apex rounded and usually more or less deeply notched, frequently with some fine denticulations; leaf blade with 3 longitudinal veins, the two lateral ones submarginal.
2. Leaf apex truncate; leaf blade with (4–) 5 longitudinal veins, the lateral ones on either side of the central vein well-spaced from the marginal veins
State Herbarium of South Australia