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Water Howellia

Howellia aquatilis
Water Howellia
Water howellia  is a flowering plant that grows underwater in Montana, Idaho, Washington, and California.  Water Howellia gets its name from Thomas and Joseph Howell, the botanists who first collected samples near Portland, Oregon along the Columbia river. This plant species was listed as threatened on July 14, 1994. Water howellia grows exclusively in small seasonal  freshwater wetlands.  These shallow ponds follow an annual cycle of filling up from in the spring and drying out in the summer.  Seeds require dry months to germinate and wet months to grow and flower. Water howellia has numerous leaves and its flowers grow above and below water. Ponds with howellia are often bordered by deciduous trees (trees that lose their leaves in the winter) such as quaking aspen or water birch.  You may also find shrubs such as red-osier dogwood or chokecherry.  Forests surrounding howellia wetlands are dominated by ponderosa pine.
Howellia grows from an elevation of 10 ft in Washington to 4,420 ft in Montana.  Seeds disperse at the same time flowers begin to bloom around late June.  The plant flowers until August.  Seeds germinate in fall only when the soil is dry enough.  Howellia overwinters as a seedling.  Studies show that seeds may still remain viable after two years of wet conditions that prevent soil from drying out. On the other hand, seeds that don’t germinate because it is too dry will not last till the next season.  In any case, seeds probably can’t survive dramatic changes in flooding and drying cycles. Water howellia is threatened by timber harvests.  Removing trees causes sediment to flow unobstructed into vernal pools.  More sediment changes the conditions for growth and plants besides howellia are favored. Removing trees also means removing shade, which may increase evaporation, causing the pool to dry out too early.
Extensive livestock grazing poses another threat. Individual plants are uprooted and seeds at the bottom of the wetland are disturbed when livestock come to drink from the pools.  Increased nutrients from livestock waste flows into the wetland and changes which plants grow there.  Livestock grazing may be the cause of howellia decline in California. Non-native species such as reed canarygrass can dominate wetland habitat.  Other plants cannot compete and survive because reed canarygrass changes the water levels of wetland areas.
Howellia loses its habitat to residential development by draining and filling, especially in Spokane County, WA.  Wetlands were also lost by dam construction along the Columbia and Willamette Rivers. Road construction has also changed the natural landforms of wetlands in Montana and Washington. Howellia is sensitive because it can only grow in a seasonal zone of the wetland.  The plant lacks genetic variation to adapt to changes in its habitat.  Even a slight change of water or sediment level, or the water’s chemical composition could put a population of howellia at risk.
The good news is that much of known occurrences of Howellia aquatilis is found on protected lands.  The Refuge contains 35 of 170 known occurrences of this species.  Other significant clusters of occurrences are in the Swan River Valley of Montana,  the southern Puget Sound, the lower Columbia River floodplain, and Mendocino National Forest in northern California.  Most protected areas have developed management plans to conserve this species that include exclusion of grazing, watershed improvements and control of invasive species. The extent of water howellia on unprotected private lands is not well known.  There are hundreds of wetlands within the Channeled Scablands near the refuge that have potentially suitable habitat. The Refuge and the Partners for Fish and Wildlife Programs having been working with landowners to restore and protect additional howellia habitat.

Facts About Water Howellia

An annual aquatic species    

Multi branched floating or submerged stems   

Can grow up to 2 feet in height    

Listing Status: Threatened  

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Last Updated: Jan 31, 2013
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