It seems to me that the roots of M. verticillatum (whorled) on Lake Arrowhead differ from those of the non-native M. heterophyllum (variable water milfoil) ... The roots on M. verticillatum do not have a branched, filamentous and fibrous look to them - they are mostly single unbranched strands only (I made sure to definitively ID M. verticillatum by its club-shaped winter buds in September before making this determination). It has also been noted that specimens of M. verticillatum slide very easily out of the substrate as a complete, intact sample, but M. heterophyllum roots require a lot more tugging and manipulation to free them.
