These plants are strictly aquatic and cannot withstand emergence. The leaves are in dense whorls, varying in size, number, and other characters (but more than 4 at a node, unlike Myriophyllum); depending in part on water depth, internode length is also extremely variable. This is our only genus of aquatic vascular plants with whorled, dichotomously forked leaves.
Reproduction is usually by simple fragmentation of the rather brittle stem, on which the internodes are much shortened toward the tips, the more dense leaves giving the characteristic bushy “coontail” appearance. The fruit is a relatively large achene (body at least 4 mm long) and in our species bears conspicuous spines, including the long, hard, terminal style, but is rarely seen. The flowers are inconspicuous, unisexual (plants monoecious), sessile or nearly so, lacking a perianth but subtended by a 10–12-parted involucre of cleft bracts. Although Ceratophyllum lacks roots, the plants are usually anchored in the substrate by pale, whitish, modified leaves and are not necessarily free-floating, as often described.
1. Achene with only 2 spines (± basal) besides the style, not winged on sides; foliage usually ± stiff, and no leaves forked more than twice.
1. Achene with several spines on each margin, their bases connected by a low but distinct wing; foliage usually very limp, and with at least some (larger) leaves of main axis forked 3 (–4) times.
All species found in Ceratophyllum
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. June 25, 2017. http://michiganflora.net/genus.aspx?id=Ceratophyllum.