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Perennial aquatic herb from a fibrous root; stems simple or few branched above, solitary, glabrous, 0.5-2 m long.
Basal leaves lacking; lower leaves submersed, short-stalked, essentially whorled, 3-parted almost to the base, the lobes many times forked into threadlike segments, glabrous, 1.5-4 mm; upper leaves emergent, few or rarely lacking, unstalked, lanceolate to egg-shaped, glabrous, sharply toothed, 1-3.5 cm long.
Heads with ray and disk flowers, few, solitary and terminal at the ends of branches; involucres 12-20 mm tall; involucral bracts about 5-6, the outer ones egg-shaped, thickly leafy, the inner ones oblanceolate, more or less membraneous, narrowly yellow-margined; ray flowers golden yellow, usually 8, 1-2 cm long; disk flowers yellow.
Achenes cylindric, somewhat compressed, fine-nerved, yellowish or greenish-brown, 10-14 mm long; pappus of 3-6 firm bristles, these longer than the achene, reverse-barbed above, smooth below.
Although I agree with Cronquist (1955) that there is little to be gained by recognizing this taxon as a monotypic genus, I have included it in Megalodonta since it appears that most future North American treatments will also recognize this genus.
Source: The Illustrated Flora of British Columbia