Flower:

Separate male and female flowers on the same plant (monoecious). Flowers are few, inconspicuous, alternating with leaves at the leaf nodes, about 2 mm long, stalkless, the males with pink to red stamens, the females with a single, yellowish, spine-like style.

Leaves and stems:

Plants are entirely submersed. Leaves are whorled all along the stem with 5 to 12 leaves in a whorl, the whorls 1 to 2+ inches in diameter. Leaves are limp, the largest usually forked 3 or 4 times with thread-like segments that are toothless or have a few minute teeth along the edge. Leaves are stalkless and often conspicuously inflated just above the base.

Whorls at stem and branch tips may be more crowded and compact than farther down the stem, but not dramatically so.

Stems are light green to reddish, brittle and easily break apart, smooth and much branched, the branches ascending to spreading. Plants have no roots and may be free floating but are more often anchored in the substrate by whitish modified leaves. Turions (winter buds) are formed later in the season, drop off the parent plant and form new shoots the next spring.

Fruit:

Fruit is an oval, slightly flattened seed with 2 spines at the base, one at the tip, and several along the edges, all connected by a narrow wing. Rarely the spines at the base are absent.

Fruit is dark green to brown at maturity, 4.5 to 6 mm long, excluding the spines. Spines are straight to curved, the basal spines 1 to 5 mm long, the terminal spine 1.5 to 7.5 mm long, spines along the edges 2 to 13 mm (to ½ inch) long.

Notes:

Spiny Coontail is occasional in Minnesota, where it reaches the western edge of its range, except for disjunct populations on the west coast. It produces very little seed and spreads mostly vegetatively, from stem fragments and turions, though it is not known to form large or dense mats. It is becoming uncommon to rare in much of its range due to habitat destruction, pollution and invasive species. It prefers clear, slightly acidic waters that may be transitory, such as beaver ponds.

Ceratophyllum species are recognized by forked leaves that are whorled all along the stem with 5 to 12 leaves in a whorl, flowers at the leaf nodes, fruit that have a spine at the tip and usually spines at the base and/or along the edges; plants lack roots and are completely submersed, commonly anchored in the substrate by modified leaves. C. echinatum has 5 or more leaves in a whorl, leaves are limp, barely toothed, often inflated just above the base, the largest leaves forked 3 or 4 times with thread-like segments; fruit has a narrow wing and spines along the edges. It most closely resembles C. demersum (Common Coontail), which is much more common, has 6 or more leaves in a whorl, leaves are forked only once or twice and have more conspicuous teeth, the leaf segments are broader and more firm, and fruit lacks spines along the edges with only a pair at the base and one at the tip.

The overall form of Ceratophyllum is like some other aquatic species, notably Myriophyllum (Water Milfoil), all but one of which have leaves whorled in 4s, the leaves compound with a central stalk and multiple spreading leaflets, and most with an emersed terminal spike of flowers and fruits.