Scientific name: Potamogeton pectinatus L.
Common name: Fennel Pondweed
Description
Habit: Aquatic perennials. Stem not compressed. Hybrids are rather frequent in this genus.
Leaves: Leaves mostly alternate, some opposite, submerged, subtending inflorescences, all with membranous sheath or stipules; submerged leaves, linear or thread-like, usually less than 2mm wide, but occasionally wider, obtuse or acute, stalkless, 3-5-veined but laterals very faint; stipules united with the leaf-base to form a sheath with free margins, wrapped around the stem, open, convolute, usually white-margined.
Flowers: In spikes or heads; spike consisting of 4-5 whorls of flowers, at first cylindrical, later becoming more or less interrupted; peduncle very slender and flexuous; usually borne above the water-surface; perianth of 4 free, greenish segments; carpels usually 4, free; stamens 4, anthers stalkless, attached to the base of the adjoining perianth-segment.
Fruits: Drupes or achenes, 1 or more present, 3-5mm, brown, with a short but distinct beak, with thick pericarp, soft on outside but with bony inner layer.
Habitat: Lakes and ponds, more rarely in rivers or canals, usually in base-rich and sometimes brackish water.
Distribution: Frequent near the coast, occasional inland.
Native status: Native
Of conservation interest: No