Myriophyllum heterophyllum Michx.

various-leaved water milfoil, variable-leaved water milfoil

Lakes, ponds, and quiet water of streams. Sometimes quite abundant.

Forb/herb

Perennial

Vascular

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Early floristic accounts of Myriophyllum heterophyllum in NY considered it to be rare and restricted to the western and central part of the state (Beckwith and Macauley 1896, House 1924, Wiegand and Eames 1926, Zenkert 1934). This is inline with recent assessments of the native range of this species (Thum et al. 2011), which recognize its native distribution as the southeastern Atlantic Coastal Plain and interior continental US. Therefore, in NY, we consider this species native. Reports of this species as well as herbarium documentation indicate that it began to show up in eastern and southeastern NY, as well as New England, as early as the 1930s (Muenscher 1935, Les and Mehrhoff 1999). Currently it is widespread in northern, eastern, and southeastern NY (as well as New England). In this northeastern range, it is considered nonnative and invasive (Les and Mehrhoff 1999, Moody and Les 2002). Because it is considered invasive in this region, New York State regulates it as an invasive species and among other things prohibits its sale. So in NY, this species has the odd circumstance of being considered native and being regulated as a nonnative invasive species, but see below.

Molecular data indicates that within the native range there are two divergent clusters of genotypes (lineages), which correspond to plants from the interior continental US and southeastern Atlantic Coastal Plain (Thum et al. 2011). Thum et al. (2011) found that plants in the introduced range in New England and nearby NY were the result of multiple introductions and represent the Atlantic Coastal Plain and continental lineages as well as hybrids between M. heterophyllum and M. laxum. Although this hybrid very likely occurs in NY, documentation has not been found. These three separate groups appear to have different growth characteristics with the Atlantic Coastal Plain lineage and hybrids producing more biomass than the continental lineage (Tavalire et al. 2012). Gene flow between the Atlantic Coastal Plain and continental lineage of M. heterophyllum appears not to occur, even when the two lineages grow together (Tavalire et al. 2012). It is possible that some of the differences between lineages represent cryptic speciation (i.e., there may be more than one species in what is currently called M. heterophyllum) and further research is warranted.

Native OBL (NWPL) OBL (NWPL EMP) OBL (NWPL NCNE) S5 (State Rank) G5 (Global Rank)

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