Threatened and Endangered Species Water Howellia Fact
Threatened and Endangered Species: Water Howellia Howellia aquatilis
OFFICIAL STATUS: Threatened. Threatened species are species that are likely to
become endangered within the foreseeable future throughout all or a significant
portion of their range.
LISTED: 59 Federal Register 35860; July 14, 1994.
HISTORICAL STATUS: Water howellia once occurred over a large area of the Pacific
Northwest region of the United States, from Oregon to California, and west to
PRESENT STATUS: Water howelia is known to occur in California, Idaho, Montana,
and Washington and is believed to be extirpated from Oregon. In Montana,
populations are recorded from Lake and Missoula Counties.
HABITAT: Howellia grows in firm consolidated sediments associated with glacial
potholes and former river oxbows which flood in spring but usually dry to some
degree by late summer Microhabitats include shallow water and the edges of deep
ponds that are partially surrounded by deciduous trees such as black cottonwood
and aspen. Ponds are generally found in Engelman spruce or lodgepole pine
LIFE HISTORY: Water howellia reproduces only by seed which germinates as ponds
dry and seeds are exposed to air. This results in annual variability in
population size depending on the extent of the previous season’s drying.
Flowering occurs from July to August.
AID TO IDENTIFICATION: Water howellia is a winter annual, aquatic plant that
grows 4-24 inches in height. It has extensively branched, submerged or floating
stems and narrow, linear, alternate (sometimes opposite) leaves up to 2 inches
in length. Two types of flowers are produced: small, inconspicuous, axillary
flowers beneath the water surface and small, white, irregular flowers in a leafy
inflorescence at or above the water surface.
REASONS FOR DECLINE: Howellia is threatened by loss of wetland habitat and
habitat changes due to timber harvesting, livestock grazing, residential
development and competition from introduced plant species; notably reed canary
grass and purple loosestrife.
RECOMMENDATIONS: Contact the U.S. Fish and Wildlife Service prior to initiating
any activities that may affect water howellia habitat.
COMMENTS: The lack of genetic variation between populations of water howellia,
and its extremely specialized habitat requirements add to the vulnerability of
REFERENCES: Federal Register- Vol. 59, No. 134, Thursday, July 14, 1994.
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