Water howellia (Howellia aquatilis) is a winter annual aquatic plant that grows 4-24 inches high. It has extensively branched, submerged or floating stems and narrow, linear, alternate (sometimes opposite) leaves up to 2 inches in length. Water howellia usually flowers in May and June, with small trumpet-shaped blooms ranging from white to light purple in color, at or above the water surface. There may also be small axillary flowers beneath the water surface.
Water howellia reproduces only by seed which germinates when ponds dry during fall. This results in annual variability in population size depending on the extent of the previous seasonâs drying. Flowering occurs from June to August.
The plant grows in areas that were once associated with glacial potholes and former river oxbows that flood in the spring, but usually dry at least partially by late summer. It is often found in shallow water (1-2 meters) and on the edges of deep ponds that are partially surrounded by deciduous trees such as black cottonwood and aspen.
States in which Howellia aquatilis is known to occur: Currently known from California, Idaho, Montana, and Washington. Historically found in Oregon. The plant has also been found on Turnbull National Wildlife Refuge in Washington.