An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
LEAFY PONDWEED-Potamogeton foliosus Raf.
DESCRIPTION-Perennial aquatics from slender rhizomes; reproducing by seed, rooting at the nodes of the rhizomes, and by winterbuds. The threadlike stems, little branched below, but bushy branched above, are up to 3 1/2 feet high, varying according to the depth of the water. The alternate narrowly linear leaves are all submerged, deep green to bronze, the principal ones to l/10 inch broad, and to 4 inches long, have 3 to 5 veins, and the stipules at the leaf bases are 1/4 to 3/4 inch long. In the var. macellus, also found in Arizona, the leaves are bright green, the principal ones to 1/18 inch broad, and l/4 inch long, have 1 to 3 veins, and the stipules are l/8 to 1/2 inch long. The winterbuds are stalkless in the leaf axils or at the end of very short branches, but in the var. macellus the branches are longer.
The tiny flowers have 4 brownish petallike parts, only 1/25 inch long, are stalkless, and arranged in pairs of 2 to 12 flowers, in short headlike flower clusters (spikes). The few flower spikes, I/8 to l/4 inch long, in the upper forks of the stems are on stalks up to 1 inch long, and are slightly thickened upward. The flower clusters are above the water surface while in flower for wind pollination, but submerged by the time the fruits are mature. The nutlets are greenish brown, unequally circular, about 1/10 inch in diameter, with a prominent knife-edged, often scalloped keel on its back. The beak is erect with a broad base.
DISTRIBUTION-Leafy pondweed grows in rather shallow, still, slowly running, or swift streams, lakes, or ponds; in fresh and alkali, usually hard, or sometimes brackish water. The entire plant is submerged except the flowers. It has become a nuisance in the irrigation ditches and reservoirs in the commercial cropland areas in Arizona. Often the plants are so dense as to actually retard the water flow. Found in Coconino, Mohave, Maricopa, Gila, Pima, and Santa Cruz counties; 1,000 to 8,500 feet elevation; flowering July to October.
Copyright (c) 1972 The Arizona Board of Regents