Equisetum hiemale var. intermedium A. A. Eaton, Fern. Bull. 10: 120. 1902, pp., and in Gray's New Manual, 53. 1908.
The sheaths are ampliated but not campanulate, and the teeth
are caducous. Described by Mr. Eaton as with the anatomy of
Equisetum hiemale but material distributed by him shows a variable
anatomy, sometimes that of H. prealta sometimes that of H.
laevigata. Collected at Port Huron, Michigan, by Mr. C. K.
Dodge. It has been found in various localities from the Atlantic
to the Pacific and may be looked for whenever H. laevigata and
H. prealta var. affinis may be found in close association.