Elodea canadensis is native to North America and not a concern (don't release it anyway because it may carry non-native organisms from your tank). Egeria densa is the invasive species (not necessarily in New York as the state does not have specific laws). Both can be referred to as anacharis, which is an outdated genus name. The former has three leaves per whorl, and the latter one has four or more.
Last edited by chibikaie; 10-20-2012 at 04:13 PM.