Acorus

1. Leaves lacking a single prominent raised midvein, but with 2–several clearly separate veins of ± equal strength along with numerous fainter veins, the leaf thus not obviously ridged to the naked eye; fruit maturing.

A. americanus

1. Leaves with a single prominent raised midvein (best observed at about 1/2 to 2/3 of the length of the leaf) that is much more conspicuous than any other veins, appearing as a ridge to the naked eye; fruits not maturing.

A. calamus

All species found in Acorus

Acorus americanusSWEET-FLAG 
Acorus calamusSWEET-FLAG, CALAMUS 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. September 25, 2017. http://michiganflora.net/genus.aspx?id=Acorus.