Light Needs: Medium
Plant Structure: Stem
Region: South East Asia
Location: All Continent except Antarctica and South America
Size: Individual Stem Grow up to 9m in length
Growth Rate: Fast
Can Be Grown Emersed: Yes
Hydrilla (waterthyme) is a genus of aquatic plant, usually treated as containing just one species, Hydrilla verticillata. It is native to the cool and warm waters of the Old World in Asia, Africa and Australia, with a sparse, scattered distribution; in Australia from Northern Territory, Queensland, and New South Wales.
The stems grow up to 1–2m long. The leaves are arranged in whorls of two to eight around the stem, each leaf 5–20 mm long and 0.7–2 mm broad, with serrations or small spines along the leaf margins; the leaf midrib is often reddish when fresh. It is monoecious (sometimes dioecious), with male and female flowers produced separately on a single plant; the flowers are small, with three sepals and three petals, the petals 3–5 mm long, transparent with red streaks. It reproduces primarily vegetatively by fragmentation and by rhizomes and turions (overwintering), and flowers are rarely seen.They have air spaces to keep them upright.
Hydrilla has a high resistance to salinity compared to many other freshwater associated aquatic plants.