OF SOUTH AUSTRALIA. 
11 
THE CLASSES OF SEA PLANTS. 
Sea plants belong to two different classes. The one bears anthers and 
ovaries, and forms a complex fruit and seed on the same plan as some of 
the less highly developed terrestrial flowering plants. The other class 
produces, sexually or non-sexually, single-celled spores. The first are 
Monocotyledonous Angiosperms, the second, or Seaweeds proper, are Algae. 
SEA PHANEROGAMS. 
Of the Phanerogams or Angiosperms there are very few forms. Probably 
not a dozen kinds occur on our Australian shores. In South Australia we 
have the genera Halophila, Posidonia, Zostera, and Gymodocm. 
Halophila is assigned by botanists to the Family Hydrocharitaceae, to 
which belong the freshwater plants Hydrocharis (Frogbit), Ottelia, and 
Vallisneria. It has a slender green stem which creeps along the bottom 
in mud or sandy debris, and bears successive pairs of opposite, bright- 
green, broadly elliptical leaves, 1.3 to 5 cm. long on long petioles. These 
leaves closely resemble those of Ottelia , on a smaller scale. The flowers, 
very different from the large, white petaloid flowers of Ottelia , are enclosed 
in a spathe, green and inconspicuous, with 3 sepals but no petals, 3 anthers 
and a one-celled ovulary. The fruit is globular with numerous seeds. The 
plants are most abundant in fairly deep water, but apparently are only 
found flowering or fruiting in quite shallow water where they are exposed 
more directly to sunlight. There is but one species in South Australia, 
H. oualis (R.Br.) J. Hooker. 
The remaining genera are placed in the family Fluviales , or 
Potamogetonaceae , to which belong the pond and river weeds Triglochin , 
Potamogeton, and Naias. Posidonia and Zostera often form extensive 
meadows on the seafloor, the former in rather deeper, the latter in shallow 
water. Zostera flats are often uncovered at low tide. 
Posidonia has a basic stock, clustered with flat sheathing leaves. The 
leaves grow to a length of from 30-90 cm., and have a width of 6 to 12 mm. 
The leaves are tough and fibrous and the base of the plant becomes 
covered with the fibrous remains of the leaf-sheaths. Presently, as the 
softer tissues decay, the base fibres are torn off by wave action and are 
rolled together into close balls, often of considerable size. Vast numbers 
of these balls sometimes strew the beach. Flat flowering stems rise, 30-60 cm. 
high, bearing 3-4 spikes at a distance from one another, each about 5 cm, 
long. The flowers, 6-12 in each spike, are enclosed in a long bract. There 
are 3 short peltate sepals, no petals, 3 anthers on a short common filament, 
and a single 1-seeded carpel. The fruit is ovoid-lanceolate, 14-16 mm. 
long, with a succulent pericarp. When ripe, the pericarp splits into four 
