Wolffia columbiana Karst.
Habitat: Ponds and still waters. [Open water (non-forested, wetland)]
Range: Southern Maine to southern Ontario and Minnesota, south to South America.
Aids to Identification: This tiny aquatic plant is the smallest of all flowering plants. It is found floating low in the water with a small portion in contact with the air. It is ellipsoid or spherical in shape, 0.8 - 1.4 mm in length, with no veins or roots. Often there is more than one layer of plants causing some to be wholly submersed. It is similar in appearance to Wolffia brasiliensis, but W. brasiliensis is punctate (dotted) with brown pigment-cells.
Ecological characteristics: Columbia water-meal often grows in association with Lemna species (duckweed).
Phenology: Reproduces by vegetative budding. Flowers are rarely produced.
Synonyms: Bruniera columbiana (Karst.) Nieuwl.
Known Distribution in Maine: This rare plant has been documented from a total of 9 town(s) in the following county(ies): Cumberland, Kennebec, Knox, York.
Reason(s) for rarity: At northern limit of range.
Conservation considerations: Possibly under-reported in southern Maine.