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Introduction
Wollfia borealis is a tiny perennial, clonal aquatic plant that lacks roots and definite leaves or stems. It is found in North America across the more northern US states (CA, CO, CT, IA, ID, IL, IN, KS, KY, MA, MD, MI, MN, MO, MT, NC, NE, NH, NJ, NY, OH, OR, PA, SD, TN, UT, VA, VT, WA, WI) and is reported in Canada in BC, Alberta, Ontario and Quebec (USDA 2010). It is found in lakes, ponds and ditches, and has been reported in BC from several locations in the lower Fraser Valley. In his essay on the rare plants of the Fraser Valley, Lomer (2011) says:
"Rarely seen in the Fraser Valley (Ceska & Ceska 1980), this miniscule aquatic plant looks like nothing more than green scum. It is proving to be more common than first thought, but is rather sporadic from year to year. New sites from Cultus Lake, Vancouver (UBC: Lomer 6754) and Cheam wetlands suggest it occurs from one end of the Fraser Valley to the other, especially in the central valley. It is not endangered as long as there are sloughs and Typha ponds and lakeshores. Easily overlooked, but uncommon nevertheless. It often grows with Lemna and Spirodella and is presumably spread by ducks so it can show up just about anywhere that ducks feed and where water is adequate. It can have explosive exponential growth late in the season, but is so tiny that only several square meters are covered in most instances."
Species Information
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expanded illustration for this species.
General: Fronds annual, free-floating, elliptic to egg-shaped, nearly twice as long as wide, 0.5-1.2 mm long, dark green, upper surface flat with 15 to 100 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.
1. Frond elliptical to egg-shaped, nearly twice as long as wide, with point at apex bent upwards.......W. borealis
1. Frond globe-shaped, about as long as wide............................W. columbiana
Habitat / Range
Ponds, lakes and slow-moving streams in the lowland and montane zones; rare in the lower Fraser Valley and SE BC (Creston); disjunct in ON and PQ and S to CT, NC, TN, MO, KS, CO, UT and CA.
Wolffia borealis is very similar in appearance to Wolffia columbiana, but can be separated from that species by shape, number of pores, and colour: W. borealis is dark green in colour, while W. columbiana is a paler translucent green (Hickman 1993).
