Hydrilla Rich.

1 species native Aust.; all states and territories except Tas.

Hydrilla verticillata (L.f.) Royle

Submerged, dioecious herb. Stems elongated, branching, with adventitous roots. Leaves serrulate, often crisped, sessile in whorls of 3–4 or opposite. Flowers unisexual, sessile in the leaf axils, solitary within a spathe. Perianth segments 6, in 2 rows. Stamens 3. Ovary 1-locular, with 2–3 parietal placentas; style 3- or rarely 2-fid. Coast and Cumberland Plain. Plants form dense masses in still water. Fl. spring–summer. Water Thyme