Ranunculus ambigens S. Wats.
Habitat: Sloughs, ditches, and muddy swamps. [Open water (non-forested, wetland)]
Range: Georgia to Louisiana, north to Maine and west to Minnesota. Somewhat scarce throughout range, although not rare in most of it. Listed as rare in New Hampshire, Delaware, and Virginia.
Aids to Identification: An aquatic or amphibious buttercup with 5-10 mm long yellow petaled flowers in small clusters at the ends of the branches. The trailing or weakly upright stem has alternate leaves, 5-15 cm long, which are entire, narrowly elongate, and toothed. With one exception, other aquatic or amphibious buttercups in Maine have either white flowers or have the upper leaves lobed or divided. The exception, R. flammula, is a common amphibious species on exposed shores or in shallow water which forms prostrate mats of filiform stems. It has smaller leaves, usually less than 5 cm long, and petals only 3-7 mm long. The longer sepal of R. ambigens (5-7 cm long) further distinguishes it from R. flammula (sepals 2-4 mm long).
Ecological characteristics: Found in slow moving or still water. Little is currently known of Ranunculus ambigens in Maine.
Phenology: Flowers June - September.
Synonyms: Ranunculus obtusiusculus Raf.
Known Distribution in Maine: This rare plant has historically been documented from a total of 6 town(s) in the following county(ies): Cumberland, Hancock, York.
Reason(s) for rarity: At northern limit of range.
Conservation considerations: Unknown; no current locations for this species are documented.