Northern Prairie Wildlife Research Center
Aiken, S. G. 1981. A conspectus of Myriophyllum (Haloragaceae) in North America. Brittonia 33:57-69. Love, A. 1961. Some notes on Myriophyllum spicatum. Rhodora 63:139-145. Nichols, S. A. 1975. Identification and management of Eurasian water milfoil in Wisconsin. Trans. Wisconsin Acad. Sci. 63:116-128.
Patten, B. C., Jr. 1954. The status of some American species of Myriophyllum as revealed by the discovery of intergrade material between M. exalbescens Fern. and M. spicatum L. in New Jersey. Rhodora 56:213-225.
|1||Upper floral bracts entire; lower bracts entire, serrate or pinnatisect, not more than 2X longer than their subtended flowers.||M. exalbescens|
|1||Upper floral bracts entire to serrate or pinnatisect; lower bracts serrate or pinnatisect, usually more than 2X longer than their subtended flowers.||Lead 2|
|2||Upper bracts shorter than or equaling their subtended flowers, only the lower bracts exceeding their flowers; stamens 8.||M. verticillatum|
|2||All bracts conspicuously exceeding their subtended flowers; stamens 4.||Lead 3|
|3||Bracts laminate, mostly oblong-lanceolate to ovate-lanceolate, pectinate below to serrate above in the spike, the lowermost distinctly different from the foliage leaves.||M. heterophyllum|
|3||Bracts not laminate, mostly linear, finely pinnatisect below to pinnatifid or shallowly toothed to subentire above in the spike, the lowermost similar to the foliage leaves.||M. pinnatum|