8. Potamogeton pectinatus L. (fennel‑leaved pondweed, sago pondweed)

Pl. 191 a, b; Map 777

Stuckenia pectinata (L.) Börner

Coleogeton pectinatus (L.) Les & R.R. Haynes

Plants with slender rhizomes ending in white tubers. Stems usually branched, circular in cross‑section, lacking purplish black spots or glands at the nodes. Leaves all submerged, the leaf blades flat, with 1 main vein, 3–10 cm long, 0.5–1.5 mm wide, linear, the tip pointed, the base tapering, sessile, the margins entire, the stipular sheath 1–4 cm long, fused to the leaf base in the basal 1/2–4/5 and usually clasping the stem. Spikes 1–4 cm long, the stalks 3–10 cm long, slender. Fruits 3.0–4.5 mm long including the curved, 0.4–0.6 mm long beak, obovate, the sides rounded, sometimes each with a low, rounded ridge, the back acute or sometimes with a low keel, lacking a toothlike basal appendage. 2n=78. May–September.

Scattered nearly throughout Missouri (nearly worldwide, except for Australia and the Pacific Islands). Submerged aquatic in a variety of still or moving waters, including ponds associated with alkaline seeps.

The leaves of this species have a bigger length‑to‑width ratio than do those of other narrow‑leaved Missouri pondweeds. The relatively long stipules sometimes overlap on the stems, and the spreading mass of leaves often appears fan‑shaped under the water.