Myriophyllum Linnaeus. Water-milfoil.

Contributed by B.A. Sorrie and A.S. Weakley

Key to Myriophyllum

A genus of about 68 species, aquatic and wetland herbs, cosmopolitan, with a primary center of diversity in Australia and secondary centers in North America and Asia. The species taxonomy and infrageneric classification used here follow Moody & Les (2010).

Key advice:Stranded plants of M. heterophyllum and M. humile (and perhaps others) produce leaves that are reduced in size. Leaves and bracts become pectinate or pinnate, so that plants resemble M. pinnatum. Such plants are the source of nearly all inland records of M. pinnatum in the VA-NC-SC-GA area. M. heterophyllum usually flowers and fruits when stranded and may be distinguished from M. pinnatum by its much denser disposition of leaves and bracts, and by its dull red fruits obscurely tuberculate (vs. tan or pale brown fruits strongly tuberculate). From stranded M. humile, M. heterophyllum may be distinguished by leaves and bracts which are clearly whorled and much more densely disposed. M. humile differs from M. pinnatum by its wholly alternate leaves and bracts, and by its smooth fruits.

Ref: Aiken (1981); Crow & Hellquist (2000a); Moody & Les (2010); Scribailo & Alix (2021) In Flora of North America Editorial Committee (2021). Show full citations.

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