The Ceratophyllaceae is a cosmopolitan family of specialized aquatic herbs entirely without roots, comprising a single genus.

Distribution
Ceratophyllum is found almost throughout the world in floating masses that can form very rapidly and choke waterways.

Diagnostic features
The species of Ceratophyllum are entirely submerged herbs that cannot tolerate periods of emergence. Roots are completely lacking, even in the embryo, but sometimes colorless, root-like branches develop which anchor the plant to the substrate. The stems are usually branched but never develop more than one branch at a node. The leaves are whorled with three to ten leaves at a node. Each leaf is rather rigid, often brittle, and one to four times forked; the ultimate leaf-segments bear two rows of minute teeth and are tipped by two bristles.

The flowers are unisexual and solitary in the axil of one leaf in a whorl. Male and female flowers are usually found on alternate nodes. The perianth consists of eight to 12 linear, bract-like segments that are united at the base. The stamens are numerous; the filaments are short or absent but the connectives are prolonged apically into short spurs. The anthers are extrorse. The ovary is superior, solitary, comprising one carpel with a single pendulous ovule. The fruit is a one-seeded nut, tipped by a persistent, spine-like style and often with additional basal or marginal spines

Classification
Ceratophyllum is very variable and at the species level taxonomically difficult. There are two well-defined cosmopolitan species, Ceratophyllum demersum and C. submersum. More than 30 local species have been described and defined mainly on the basis of fruit-spine number and position, but most of them are probably no more than variants of the main species.

The family as a whole is highly specialized and very reduced aquatics. They lack roots, cuticle, stomata and woody or fibrous tissue. The flowers are also reduced and specialized for pollination under water. The pollen is without an aperture, smooth and with a very thin exine (outer wall). The lack of comparable characters makes it difficult to determine the affinities of this family. It is usually considered to be allied to the Nymphaeaceae. The one-seeded fruit, and the seed containing a large embryo with large, fleshy cotyledons, a well-developed plumule but no radicle, endosperm or perisperm suggest a particular relationship with the genus Nelumbo (Nymphaeaceae).

Economic uses
Ceratophyllum usually floats in mats just below the surface of the water. These mats provide a valuable protection for fish fry but also provide protection for bilharzia-carrying snails and malaria- or filaria-carrying mosquito larvae.