Plant Profile - Hydrilla

It sure has been a busy week for us here at AERF!  As a result, our blog has been rather quiet, however we hope to leave you with something special for the weekend.  Often you will see us reference different plants in our facebook, twitter, and blog postings.  You may, more often than not, find yourself scratching your head as to what exact plant we are actually talking about.  To give our readers a little more background into the plants we so often discuss, we bring you the AERF Update's "Plant Profile" section.

A single hydrilla plant.  Photo Credit:  NCSU

It only seems appropriate that we have our first "Plant Profile" feature one of the the most prevalent and problematic aquatic invasive plant species in the world!  Hydrilla (H. verticillata) is by far one of the most well known submersed invasive plant species which can have both deleterious environmental and economic effects.  For starters, let’s talk about how exactly Hydrilla found it's way into United States and what makes it such a problem for our nations water bodies.

Hydrilla actively growing in the water column

Hydrilla was first discovered growing in Hillsborough County, Florida during the early 1950s. By the early 1970s it had all but taken over every major water body in all drainage basins in the state. Today, Hydrilla continues to spread within the sunshine state, encompassing over 100,000+ acres of water in of Florida's public lakes. The troublesome invader can now be found in all Southeastern States, as far north as New York, and in many western states including California.  For more information on how Florida combats hydrilla, click here.

Hydrilla can cause problems in a water body for a number of reasons. For one, once hydrilla invades an aquatic ecosystem with diverse plant life, it often drives out all native aquatic plants that may benefit that particular ecosystem. Hydrilla's competitive edge comes from a number of unique life strategies. The plant can grow in less than 1% of sunlight, allowing it to begin growing much earlier in the growing season and to survive at greater depths (up to 20+ feet). The plant can also withstand a wide range of climates, having been found as far north as Russia, northern China, and Poland.  Even coastal areas are threatened by Hydrilla the plant has been found to sustain growth in water of near 50% the salt content of the sea. To be honest, there are very few bodies of water in the world in which Hydrilla can't establish.  To see a distribution map of hydrilla, click here 


Hydrilla also has excellent survival and dispersal strategies. Hydrilla spreads via fragmentation meaning that the plant breaks apart (either by natural breaking or disturbance from boat propellers) and can produce entirely new plants!  If that’s not bad enough, Hydrilla also produces special survival structures called tubers and turions. The turions break off the stems in the fall and can drift for long distances before sinking to start a new plant. The tubers grow on the plants roots and detach in the fall producing new plants. A single tuber can lead to the production of several hundred others in the course of one season! Recent research at North Carolina State University has shown that tubers can survive for up to seven years in the sediment before sprouting. The long survival time of the tubers creates the major challenge in management of the plant. 

Hydrilla tubers.  Photo Credit:  NCSU Aquatic Weeds Program

Once sprouted, Hydrilla’s speed of growth is fast and furious. Hydrilla plants can double their biomass every two weeks during optimal growing conditions. Recent research has shown that hydrilla can produce alarming amounts of biomass during the year.  Click here for a summary of that research.  Once Hydrilla reaches the surface, it will expand horizontally covering the entire water surface while rapidly producing new stem growth through branching. It also doesn’t help that when Hydrilla was introduced into the U.S., it came without any of it’s natural enemies like herbivorous fish and insects. The voracious nature of Hydrilla and tangled mats that it forms has a number of environmental, economic and cultural impacts impeding recreation, decreasing property value, and even potentially harboring cyanobacteria which produce deadly toxins.  For more information on such toxins, click here.

Hydrilla in a North Carolina reservoir.  Photo Credit:  NCSU Aquatic Weeds Program

 For help in identification of hydrilla, visit North Carolina State Universities Aquatic Weed ID Quick Guide.  For more information on Hydrilla visit the UF-IFAS webpage.  For management options, visit the AERF BMP Manual - Chapter 13.1. 

Stay tuned next week for more of the latest in aquatic plant science, management, and innovation!