Hydrilla

Hydrilla verticillata · Aquatic plants

Out of the water · Photo: Michelle W. （鍾偉瑋） / CC BY

Invasive

Also called Florida elodea, Water thyme

State noxious weed listing

Idaho: Early detection
Oregon: A list
Wyoming: Game and Fish aquatic invasive species

How to identify Hydrilla

Leaves in whorls of 4 to 8 with sharply toothed edges
Small spines along the midrib on the leaf underside, rough to the touch
Small potatolike tubers in the mud and turions on the stems

Similar plants

Elodea and Brazilian elodea have smooth leaf undersides and do not form tubers.

Growth profile

Growing season	Grows from tubers and turions in spring, reaches the surface by summer and forms new tubers in fall.
Starts growing	About 50 to 55 F water; grows in very low light
Light	Tolerates very low light
Depth	1 to 25 feet
How it spreads	Tubers, turions, stem fragments; one inch pieces can root
Habitat	Lakes, ponds and canals, warm water; can grow in soft or hard water over many bottom types.

Why it matters in a lake

One of the worst aquatic weeds in North America; tubers can stay dormant in mud for several years. A past Idaho population is no longer known, and it is listed for early detection in Idaho.