Hardiness: Very Easy
Light Needs: Low
Plant Structure: Stem
Size: stem width two inches
Growth Rate: Very fast
Can Be Grown Emersed: No
Somewhat tricky to identify at first glance, Hydrilla verticillata (also known as water thyme, Wasserquirl, and Indian starvine) is often confused with ever popular Egeria densa (Anacharis), Egeria najas and several other aquatic plant species due to the similarity in growth form and leaf structure. In addition to a moderately serrated leaf edge and a greater number of leaves per whorl, H. verticillata sports a small barb about half way along the main leaf vein, called the midrib. The barb is a defining feature of H. verticillata as well as the formation of overwintering root nodules called turions that develop after twenty consecutive days of shortened photoperiod.
H. verticillata is widely known as an invasive plant, particularly in warmer states like Florida where it has made its way into every major water drainage system. However, it is capable of inhabiting bodies of fresh water as far north as Siberia. The ability of H. verticillata to tolerate both warm tropical temperatures up to the mid 80s Fahrenheit and overwinter in frozen environments makes it one of the most problematic aquatic weeds in the world.
Propagation of H. verticillata is very easy and is indeed the reason it has so easily spread itself across so many aquatic ecosystems, causing destruction of habitat, obstruction of water craft, a danger to swimmers and otherwise fouling the body of water in which it grows. The plant quickly ascends to the water's surface where it forms dense mats and shades other plants below. For these reasons, keeping or trading it is illegal in all states.
Since this species is so adept at overwhelming nearly all other aquatic plants and legal and more suitable alternatives are available, its use in aquascaping is of questionable value at best and should be discouraged. With more hobbyists becoming interested in native plants, it is bound to be encountered more often; it is included in this database is for the purposes of identification and education only.
Photo #1 Submersed: US and International Copyright 2009 by Michael Teesdale. All Rights Reserved.