According to Ceska and Ceska (2010), Andean watermilfoil is a "South American species that extends to western USA and to British Columbia; also in eastern Canada. It occurs in wind-swept parts of large lakes or in flowing water of rivers. Dried herbarium specimens are dark grey. The lowermost leaves are reduced to bract-like structures and the system of strong whitish roots are the best identification characters of the sterile plants. Winter buds absent."
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General:
Perennial aquatic from a rhizome; stems 20-100 cm long, simple or branched.
Leaves:
In whorls of 4 or 5, 1-2.5 cm long, comb-like and dissected into 13-21 threadlike segments, very gradually transitional to the bracts; bracts conspicuous, oblong triangular, 7-10 mm long and from comb-like to lightly sharp-toothed; winter buds absent.
Flowers:
Inflorescence simple to conspicuously forked, submersed to emergent; flowers subtended by small, whitish, erose to comb-like bracteoles 1-2 mm long; sepals whitish, more or less sharp-toothed to comb-like; petals soon deciduous, about 2.5 mm long; stamens 8, the anthers about 2 mm long; stigmas feather-like.
Fruits:
Mericarps 4, about 2 mm long, glabrous.
If more than one illustration is available for a species (e.g., separate illustrations were provided for two subspecies) then links to the separate images will be provided below. Note that individual subspecies or varietal illustrations are not always available.
Illustration Source: The Illustrated Flora of British Columbia
Synonyms and Alternate Names:
Myriophyllum elatinoides Gaudich.
There are ten species of Myriophyllum found in the Pacific Northwest (Ceska and Ceska 2010). View a key to the genus Myriophyllum for this region prepared by Oldriska Ceska and Adolf Ceska (BEN #428).
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