Ceratophyllum

Lore & Background

Ceratophyllum grows completely submerged, usually floating on the surface, with stems reaching 1–3 m in length. At intervals along nodes of the stem, it produces rings of bright green leaves that are narrow and often much-branched; the forked leaves are brittle and stiff to the touch in some species, softer in others. Roots are completely absent, even in the embryonic stage, but sometimes modified leaves with a rootlike appearance anchor the plant to the bottom. Stomata are not present on any species. The flowers are small and inconspicuous, with male and female flowers on the same plant. In ponds, it forms thick buds (turions) in autumn, which sink to the bottom and give the impression that the plant has been killed by frost; come spring, these grow back into long stems, slowly filling up the pond.

Coontails were first described by Carl Linnaeus in 1753 with Ceratophyllum demersum as the type species. The genus is considered distinctive enough to warrant its own family, Ceratophyllaceae, but was once considered a relative of Nymphaeaceae and included in Nymphaeales in the Cronquist system. Recent research has shown that the plant is not closely related to Nymphaeaceae or any other extant plant family. Some early molecular phylogenies suggested it was the sister group to all other angiosperms, but more recent research suggests it is the sister group to the eudicots, a notion supported upon sequencing of the C. demersum genome in 2020. The APG IV system placed the family in its own order, the Ceratophyllales.

More than 30 species of coontail have been described, but the specifics of how many are valid is yet to be settled. A narrow interpretation rejected over 23 of these taxa as variants, accepting only 7 species, and even creating subspecies was rejected. A 2018 phylogenetic analysis found support for 4 species being monophyletic, while 3 others are paraphyletic. It found C. australe to be a divergent lineage of C. tanaiticum, rendering C. tanaiticum paraphyletic, but still regards C. australe as a separate species due to significant morphological differences and geographic isolation. C. demersum and C. platyacanthum were recovered as paraphyletic with respect to each other, and could possibly be considered one species, although their morphologies and ecologies are distinct.

Reader's Guide

Ceratophyllum is notable as the only extant genus in its family and order, making it a unique lineage among flowering plants. Its phylogenetic position has been debated: early molecular phylogenies suggested it was the sister group to all other angiosperms, but more recent research, supported by the 2020 sequencing of the C. demersum genome, indicates it is the sister group to the eudicots. The APG IV system places it in its own order, Ceratophyllales. The genus is also distinctive for its complete lack of roots and stomata, and for producing turions that overwinter on pond bottoms. Taxonomically, the number of valid species remains unsettled, with a narrow interpretation accepting only 7 species out of more than 30 described. A 2018 phylogenetic analysis revealed paraphyly among several species, suggesting that some may be conspecific, though morphological and ecological differences have kept them separate. For aquarium and aquatic plant enthusiasts, coontails are a hardy, rootless, submerged plant that can fill ponds with long stems, and their ability to form overwintering buds makes them resilient in temperate climates.

Did You Know?

• Ceratophyllum is the only extant genus in the family Ceratophyllaceae and the only extant family in the order Ceratophyllales.
• The plant completely lacks roots, even in the embryonic stage, and has no stomata on any species.
• In autumn, coontails form thick buds called turions that sink to the bottom and regrow into long stems in spring.
• A 2018 phylogenetic analysis found that Ceratophyllum demersum and Ceratophyllum platyacanthum are paraphyletic with respect to each other and could possibly be considered one species.