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Howellia aquatilis Gray

Water Howellia

Campanulaceae (Bellflower family)

General Description: Water howellia is an annual aquatic species with fragile, submerged and floating stems 10-100 cm long. Plants are rooted in bottom sediments with stems branched several inches above the base and extending to the surface of the water. Leaves are narrowly linear, entire-margined, 1-5 cm long, and mostly alternate, or some of them subopposite or whorled in threes. Plants produce two types of flowers. Beneath the water surface there are small solitary flowers in the leaf axils that do not open. At the tips of stems emerging above the water are small, white flowers with 5 lobes on one side of the corolla. Calyx lobes are pointed and persistent in fruit. Both types of flowers give rise to capsules 1-2 cm long which contain one to five shiny brown seeds up to 2-4mm long.

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Illustration.

Field Identification Tips: When in flower, the irregular-shaped white flowers will help distinguish water howellia from many other aquatic species. The spreading, pointed calyx lobes persistent in fruit are distinctive.

Phenology: Late July to early August for the flowers at the surface. The cleistogamous submerged flowers develop in late June.

Similar Species: Superficially similar to a number of other aquatic plants, especially species of Callitriche. Callitriche heterophylla is often found with water howellia, however, it has submerged linear leaves that are usually opposite, as well as broadly obovate floating leaves. Vegetatively, small-leafed Potamogeton species can also look similar. They can be distinguished by their small flowers without any petals, much smaller seeds, and well-developed stipules. Early in the season water howellia can also resemble immature plants of Sium sauve.

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Habitat: Restricted to small, vernal, freshwater pothole ponds or the quiet water of abandoned river oxbow sloughs in the valley zone. The ponds are typically filled by snowmelt and spring rains, but dry out to varying degrees by the end of the growing season. They are generally less than 1 m deep, but plants occasionally occur in water up to approximately 2 m in depth. Bottom surfaces usually consist of firm clay and organic sediments. The ponds typically occur in a matrix of forest vegetation.

Global Distribution: Widely separated areas in the western United States. It is known from northwestern Montana (Lake and Missoula counties), three areas in Washington (Clark, Pierce, and Spokane counties), northern Idaho (Latah County), and northwestern California (Mendocino County). Historically, water howellia was also known from several areas in northwestern Oregon, and additional sites in Washington.

Idaho Distribution: A single known extant population in Latah County near the small town of Harvard. There is also a historical collection reputedly from the Spirit Lake area in Kootenai County.

References:

Bursik, R. J. 1995. Update: Report on the conservation status of Howellia aquatilis in Idaho. Status survey report prepared for Idaho Department of Parks and Recreation by the Idaho Department of Fish and Game, Conservation Data Center, Boise, ID. 4 pp.

Gamon, J. 1992. Report on the status in Washington of Howellia aquatilis Gray. Washington Natural Heritage Program, Olympia, WA. 46 pp.

Lesica, P. 1992. Autecology of the endangered plant Howellia aquatilis; implications for management and reserve design. Ecological Applications 2: 411-421.

Lichthardt, J., and R. K. Moseley. 2000. Ecological assessment of Howellia aquatilis habitat at the Harvard-Palouse River flood plain site. Unpublished report prepared for the Idaho Department of Parks and Recreation by the Idaho Department of Fish and Game, Idaho Conservation Data Center, Boise, ID. 14 pp. plus appendices.

Montana Natural Heritage Program. Montana rare plant field guide. Available at: http://nhp.nris.state.mt.us.

Shelly, J. S., and R. K. Moseley. 1988. Report on the conservation status of Howellia aquatilis, a candidate threatened species. Unpublished report prepared for the U.S. Fish and Wildlife Service, Regions 1 and 6. 166 pp.

Washington Natural Heritage Program. 1999. Field guide to Washington's Rare Plants. Cooperative Challenge Cost-share Project, Spokane District, USDI Bureau of Land Management and Washington Natural Heritage Program, Washington State Department of Natural Resources.