Potamogeton nodosus Poir.: American pondweed, longleaf pondweed. Potamogetonaceae (pondweed family).
Native perennial. Submersed plant, growing rooted in substrate from slender white rhizomes marked with red. The stem, growing to 6 ft (1.8 m), carries two forms of leaves, submersed and floating, both alternate. Submersed leaves have slender stalks to 6 in (15 cm); blades are narrow and linear, pointed at the tip and tapering to the stalk, 8 in (20 cm) long; they are thin and flimsy. Floating leaves, lying flat on the surface, are oval, rather leathery and shiny, to 4.3 in (11 cm) long, the blades taper to leaf stalks that are up to 8 in (20 cm) long. From 7 to 15 veins can be counted on the upper side, and the underside has a prominent midvein. Stipules at the base of the leaves are relatively long, to 4 in (10 cm), and pointed; those underwater are more frayed and fibrous. Flower stalks, thicker than the stem, arise from nodes of floating leaves to emerge from the water; they carry club-like spikes of densely packed, inconspicuous flowers.
Clasping Leaf Pondweeds
Potamogeton richardsonii (Benn.) Rydb.; Clasping leaf pondweed, Richardson pondweed.
Potamogeton praelongus Wulfen: Clasping leaf pondweed, whitestem pondweed. Potamogetonaceae (pondweed family).
Native perennials. These submersed species have similar traits, but differ in size. They each have only one type of leaf, and lack differentiated surface/floating leaves. In both, the alternate, stalkless leaves have wide leaf bases that clasp or wrap almost completely around the stem. In P. richardsonii the leaves are 0.8 - 3.5 in (2 - 9 cm) long, in P. praelongus they are significantly larger, 4 - 16 in (10 - 40 cm) in length. Leaves are spear-shaped, broader at the base and pointed at the tip, and smooth-edged (compare to P. crispus which has teeth along leaf margins). The leaf tips of P. praelongus are cupped or hollowed, and the tip splits if pressure is applied to flatten it. Its stems become whitish and angled at the nodes, looking zig-zag. Papery, frail stipules occur in both, being much longer in P. praelongus. Flower spikes are held at or above surface, with flower stalks about the same thickness as the stems. P. praelongus is usually found in deep water with P. richardsonii growing closer to the shore.
Potamogeton crispus L.: Curlyleaf pondweed, crisp pondweed. Potamogetonaceae (pondweed family).
Non-native perennial. This submersed plant has rooting rhizomes and stolons and lacks floating leaves; it can grow in water to 15 ft (4.5 m). Reproduction is from rhizomes and stiff, hard winter buds. Stems are pale, with reddish nodes, flat, and often angled back and forth in a zig-zag pattern. There is frequent branching and high leaf density. The alternate leaves are attached directly to the stem without stalks. They are firm, 1.2 - 4.75 in (3 - 12 cm) long, narrowly rectangular to 0.6 in (1.5 cm) wide, with rounded to broadly-pointed tips and conspicuously toothed and wavy margins. The prominent midrib is often pale to reddish. Short flower spikes are on a stalk that may curve as seeds ripen. The compact, thickened buds, or turions, are armed with stout spiky teeth on the margins of their compressed leaves. They provide efficient reproduction, but once they have fallen to the substrate are a nuisance to swimmers. This plant spreads aggressively within a season and increases its range from year to year, eliminating native vegetation. Its extremely dense stands can impair fishing, swimming and all other water uses.
Potamogeton zosterformis Fern.: Flatstem pondweed, fern pondweed, eelgrass pondweed. Potamogetonaceae (pondweed family).
Native perennial. Found in still or slow-moving water, 3.3 - 8.2 ft (1 - 2.5 m) deep, rooting from slender rhizomes. This pondweed has only submersed leaves of a single shape, and few branches. The underwater stem is flattened, or strap-like, with slight projections or wings that produce a running edge. Leaves arise alternately along the flat stem; they are narrow, linear, without a leaf stalk, smooth-edged, coming to a sharp, tough little point at the tip and narrowing slightly at the base, usually 4 - 8 in (10 - 20 cm) long, and somewhat wider than the stem. They have a smooth margin, and 3 main parallel veins. Stipules, 0.4 - 2.4 in (1 - 6 cm) long, are attached to the nodes only at the base; they fray with age. The stem of the club-like flower spike emerges from water and is usually curved.
Floating Leaf Pondweed
Potamogeton natans L.: Floatingleaf pondweed. Potamogetonaceae (pondweed family).
Native perennial. Grows in still and slow-moving water, preferring depths of about 5 ft (1.5 m). Floating and submersed leaf shapes differ; stems seldom branch. Submersed leaves are stalkless, extremely narrow, linear, and rather stiff, tapering evenly along a length of 4 - 20 in (10 - 50 cm) to a thread-like tip. Floating leaves are oval, to 4 in (10 cm) long. Leaf stalks are slender and usually longer than the blade. The base of the floating leaf blade is wider than the pointed tip; where it meets the stalk it can be slightly indented (heart-shaped) or almost straight across, making this juncture look right-angled or square-cut rather than tapered. Stipules clasp the stem; they are long and fibrous and sharply pointed at the tip. The stalk of the emergent flower spike is thicker than the leaf-bearing portion of the stem.
Potamogeton illinoensis Morong: Illinois pondweed. Potamogetonaceae (pondweed family).
Native perennial. Plants found in water to 15 ft (4.5 m) deep. Slender rhizomes form a network in the substrate; they can have red mottling. Stem is stout and branching, to 6 ft (1.8 m). Submersed and floating leaves differ, although floating leaves are often absent. Submersed leaves are linear lance-shaped, tapering at both ends, and up to 8 in (20 cm) long; a leaf stalk may be present, to 2 in (5 cm) long, or absent. These underwater leaves are thin-textured and flimsy, their edges often wavy or rippling. There is a prominent midrib on the underside; leaves may arch, but not into as pronounced a crescent-shape as in P. amplifolius. Floating leaves have a longer leaf stalk; blades are broad, leathery, oval, to 5.5 in (14 cm) long, 2.75 in (7 cm) wide, tapering or rounded at either end, and often forming a hard point at the tip. Stipules are as long as the leaf stalks of the floating leaves, firm and persistent, with two ribs or keels along the outer side. The stalk of the club-like flower spike is thicker than the stem.
Largeleaf Pondweed, Bass Weed
Potamogeton amplifolius Tuckerman: Largeleaf pondweed, bassweed. Potamogetonaceae (pondweed family).
Native perennial. This robust plant grows in water of lakes and rivers to 9 ft (2.7 m), rarely to18 ft (5.4 m). It has two types of leaves, although floating leaves are not always present. P. amplifolius is unusual for pondweeds, in that both floating and submersed leaves are wide, and the underwater leaves can be larger than those at the surface. Submersed leaves are thin and flimsy with flaccid margins; they frequently collapse or fold in half inwards, arching upwards along the prominent midrib to a crescent shape. The blades are basically oval, 3 - 8 in (7.5 - 20 cm) long, broadly pointed at the tip and tapering into the short leaf stalks. Floating leaves are flat, firm, and oval, 2 - 7 in (5 - 17.5 cm) long, and rounded, rather than tapering, at the base; 24 to 48 veins are visible on the upper surface, with several of these being ridged. The sharply pointed stipules tend to be longer than the leaf stalks of the submersed leaves and shorter than the stalks of the floating leaves; the stipules have two ridged veins down the back. The flower spike emerges from among the floating leaves; it is club-like and borne on a stout stalk.
Potamogeton pusillus L.: Narrowleaf pondweed, small pondweed, baby pondweed. Potamogetonaceae (pondweed family).
Native perennial/annual. Growing submersed, from fibrous roots, or rarely very slender rhizomes, in ponds and streams. Has numerous submersed leaves of a single shape; there are no floating leaves. The slender, sometimes flattened, much-branching stems are held erect underwater, to 3.3 ft (1 m). Leaves are alternate, narrow, ribbon- or grass-like, slightly pointed, 0.4 - 2.75 in (1 - 7 cm) long, with very slender leaf stalks. A prominent midvein is found on the lower side of the blade; one or more pairs of parallel side veins are seen. Two tiny glands, visible as hard round yellow dots, are at the base of the leaf or stipule. Stipules are thin, membrane-like, making a half- to completely-open tube around base of leaf; 0.7 in (1.7 cm) long, they wear away with age. Flower spike stalks are slender to thread-like. Plant can produce winter buds. Grows in mixed stands of plants that may cause water use/access problems.
Potamogeton robbinsii Oakes: Flatleaf pondweed, fern-leaf pondweed, Robbin's pondweed. Potamogetonaceae (pondweed family).
Native perennial. Submersed plant with a single leaf type and no floating leaves; grows up to 10 ft (3 m) but remains low in the water-column, stems often not reaching the surface until they flower. Individual leaves are rigid, linear, 1.2 - 4.75 in (3 - 12 cm) long, narrowing to a point at the tips and becoming narrower towards their bases where they meet the stem. Lower on the stem the leaves are spaced farther apart but near the top the stiff dark-green leaves emerge closer together, flattened in a single plane; they resemble fern fronds or palm leaves. They may emerge so close together that they look like stiff ribs of a fan. Stipules are pointed, up to 1.2 in (3 cm) long, and clasp the stem at their base; they often are worn away so that only the veins remain. Flower spikes are borne on slender, 1 in (2.5 cm), stalks that are stiffer and flatter than those of other pondweeds.
Stuckenia pectinata (L.) Boerner (formerly Potamogeton pectinatus) : Sago pondweed, thin-leaved pondweed. Potamogetonaceae (pondweed family).
Native perennial. An extensive network of slender rhizomes forms dense mats and anchors the plant in the substrate. Rhizomes produce spherical starchy tubers or bulblets, 0.8 in (2 cm) in diameter, at their ends. Whole plant is submersed, growing to 13 ft (4 m) in length, and branching freely near the apex so branches and leaves fan out and can become very dense at the water surface. Single leaf type, no floating leaves. Leaves are coarse and slender, grass-like, 2 - 14 in (5 - 35 cm) long, tapering to a pointed tip, with 1 to 3 veins. Stipules form a sheath up to 2 in (5 cm) long that holds the lower part of the leaf blade against the stem; the upper stipule is free of the stem and leaf. This stipule can be peeled away from the stem to reveal the lower part of the leaf and the node from which the leaf originates. The slender flower stalk, up to 4.75 in (12 cm) long, is visible in the uneven gaps between the whorls of flowers or nutlike fruits on the flowering spike. This plant can create dense stands that clog irrigation canals and produce major problems for water flow and access, but it is very important in natural habitats as a wildfowl food source.
Suckenia filiformis (Pers.) Boerner (formerly Potamogeton filiformis): Threadleaf pondweed, fineleaf pondweed, slender-leaved pondweed. Potamogetonaceae (pondweed family).
Native perennial. Whole plant is very slender and thread-like, to 20 in (50 cm) tall, growing submersed and with only one type of leaf. Stems emerge from a network of rhizomes that can form tubers at their tips. Stems to 0.04 in (1 mm) wide, and slightly flattened, branching into two near the base of the plant. Leaves are very thin, 2 - 4.75 in (5 - 12 cm) long; they have one main vein. The lower part of the stipule sheathes the stem and the base of the leaf blade; the upper part is free of the stem and up to 0.2 in (0.5 cm) long. The stipule can be pulled away from the stem to reveal the lower part of the leaf blade. Flower spike stalks are slender to thread-like; the flowers and later nut-like fruits are spaced rather than crowded along the stalk.
Variable Leaf Pondweed
Potamogeton diversifolius Raf.:Variable-leaf pondweed, waterthread pondweed. Potamogetonaceae (pondweed family).
Native perennial. Found in shallow slow-moving or still water, where thread-like rhizomes produce stems to 4.5 ft (1.4 m). This is one of the smaller pondweeds to have floating leaves and these differ from the submersed leaves in shape. Leaves are generally arranged alternately on the stem, although they can arise so close together as to look opposite. Submersed leaves are extremely narrow, thread-like, to 2.4 in (6 cm) long, and taper to a sharp bristle-like point. Floating leaves are leathery, oval to elliptical, slightly wedge-shaped or tapering at the base and tapering or rounded at the tip, to 1.6 in (4 cm) long; these leaf stalks are slender and up to 1 in (2.5 cm) in length. Stipules are present on both types of leaves and are partially attached to the base of the leaf stalk; those on floating leaves are prominent, 0.75 - 1 in (2 - 2.5 cm) long. Flowering spikes are borne at nodes of both floating and submersed leaves; the former spikes are more club-like, the latter shorter and more spherical.