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Introduction
This is a tiny floating perennial aquatic plant that lacks roots and definite leaves or stems. It is clonal and occurs in thick populations that often appear as scum on the surface of still waters, such as ditches, ponds, and lake edges. It is distinctly smaller than the more familiar duckweed (Lemna minor). View a comparative photo. In North America, Columbian water-meal is found across the US (though absent from AZ, NM, UT, CO, ID, WY, WA) and Canada (AB, BC, MB, NB, ON, QC, SK) (USDA 2010). In BC, it is so far reported only from southwestern Vancouver Island, from Swan Lake. However, it might be overlooked and should be looked for, for example, in the Lower Mainland.
Species Information
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expanded illustration for this species.
General: Fronds annual, free-floating, globe-shaped, about as long as wide, 0.8-1.3 mm long, transparent green, round except for flat center with 1 to 10 (30) stomates, usually in unequal pairs, rootless, with a pouch at the basal end from which young plants arise.
Flowers: Two, together on the upper surface, 1 female, 1 male; stamen 1; pistil 1.
In Washington, Columbian water-meal is found in association with northern water meal (Wolfia borealis), which is found in BC, and Brazilean water-meal (Wolffia brasiliensis), which is not reported from BC. Colour, shape and number of pores are used to separate it from these species (Washington Department of Natural Resources 2005). In the field, W. borealis and W. brasiliensis are dark green in colour, and W. columbiana is a translucent green (Hickman 1993). In Washington, Wolffia columbiana is found at elevations of 10 to 250 ft. (Washington Department of Natural Resources 2005). The elevational range in BC is presently unknown.
Hickman, James C. 1993. The Jepson Manual of the Higher Plants of California. University of California Press, Los Angeles.
Washington Department of Natural Resources. 2005. Wolffia columbiana page. On-line Field Guide to Selected Rare Plants of Washington. Washington Department of Natural Resources, Washington Natural Heritage Program and the U.S.D.I. Bureau of Land Management.
