|Approximately 70 pondweed species grow in temperate regions. Two of these are very common: curly-leaved pondweed and Richardson’s pondweed. The only feature these two share is their characteristic flower, a spike, on which many male and female flowers are clustered.
Their rhizomes provide both Richardson’s pondweed and curly-leaved pondweed with an effective means of reproduction. Richardson’s pondweed forms small winter shoots that break loose from the rhizome to colonize other areas. Curly-leaved pondweed propagates even more effectively since it has more than one mode of vegetative propagation. It grows early in the spring and forms very resistant buds. By the end of June, the plant is very tall and begins to lose leaves at the base of the stem while becoming highly branched at the crown. When adult plants die during the summer, the buds break loose and take root, contributing to a new late-summer growth phase.
Pondweeds thrive on fine soils such as muck, and sometimes on gravel or sand. Curly-leaved and Richardson’s pondweed can grow at depths exceeding 1 m. They are found in both stagnant water and strong currents and can tolerate a wide range of climatic conditions.
Curly-leaved pondweed is characteristic of eutrophic (nutrient-rich) waters. It can survive in sewer water, water that is turbid or clear, and even in brackish (slightly salty) water.
Richardson’s pondweed lives for more than two years (i.e., it is a perennial), thanks to its rhizomes. This species has very leafy, usually highly branched stems that may creep or grow upright. Its spikes always rise out of the water and may measure up to 3.5 cm; the whole plant can reach a considerable height (1.2 m).
Curly-leaved pondweed is fully submerged and can reach lengths of up to 1.2 m. Like Richardson’s pondweed, it is a perennial, due to its rhizomes. Its spikes are approximately 1.5 cm long. The slightly branched stems bear wavy-edged oval leaves. Curly-leaved pondweed is highly branched at the crown.