Federal and State Listed Species of Texas:
Little Aguja pondweed
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Distribution map of Little Aguja pondweed (Potamogeton clystocarpus).
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Global Location
Little Aguja pondweed is only known from the Davis Mountains in Jeff Davis County, Texas.
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Description
The perennial Little Aguja pondweed lives underwater, rooted in creekbeds. Stems are light green to brown and to 60 cm long. Where leaves arise from the stem, there are two minute circular structures which produce oil and appear white to gold, but are semi-transparent. Leaves are very narrow (0.7-1.7 mm wide) with linear sides, have smooth leaf edges and pointed tips, are 3.2-7.8 cm long, and spirally arranged on the stem. Aquatic plants float partly due to visible air chambers inside the leaves. Little Aguja pondweed has one to four rows of these air chambers on either side of the conspicuous vein running down the middle of the leaf. The flowers arise on short, erect, cylindrical stalks (3.2-4.8 cm long) from the tip of the main stem or from the same location as leaves on the main stem. These stalks bear three equally spaced groups of flowers (1.5 mm apart) and each group circles the flower stalk. The brown to yellow-green, round fruits cluster in sets of four. Running along the fruit and facing away from the fruit’s stem is a tiny, smooth ridge, like the keel of a boat. Fruits have minute elongated tips (0.2-0.6 mm) which either point straight out or are slightly curved back. Although only visible when the fruit is dry (i.e., not a good field character), the fruit has 1-3 tiny projections near its base.
Little Aguja pondweed is an aquatic perennial with narrow, linear leaves that float partly due to internal air chambers on either side of the vein running down the middle of the leaf.
Credit: Ed Schneider
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Similar Species
Leafy pondweed (Potamogeton foliosus) fruit has a ridge like Little Aguja pondweed, but the ridge is wavy. Small pondweed (Potamogeton pusillus) fruit ridges are mostly absent (appearing as a rounded surface instead). Usually leafy pondweed lacks oil-producing structures, but has flowers with club-shaped stems that curve back toward the main stem. Small pondweed has generally shorter leaves (0.9-6.5 cm). The best character for identifying Little Aguja pondweed is the presence of 1-3 tiny projections near the fruit base. However, the specimen needs to be dry for the projections to be visible. Neither leafy pondweed nor small pondweed has these projections.
Small pondweed fruit ridges are mostly absent as compared to Little Aguja pondweed fruit which has tiny, smooth ridges.
Leafy pondweed fruit has a ridge like Little Aguja pondweed, but the ridge is wavy.
Credit: C. Barre Hellquist
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Floral Characters
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Habitat
Little Aguja pondweed occurs in deeper sections of calm or slow-flowing intermittent creeks. The creek bottoms are composed of sand and gravel eroded from the surrounding mountains.
Habitat of Little Aguja pondweed.
Credit: Chester Rowell
Life Cycle Events
Fruiting usually occurs from May to October.
Survey Season
Little Aguja pondweed can usually be found year-round in deeper pools or when the creeks are running (most likely in mid- to late summer during the rainy season of their semi-arid habitat). See Comments and Similar Species sections for tips for positively identifying this species.
Comments
Identification in the field of live specimens is important for rare species because harvesting plants for identification only reduces populations more. However, it has been shown that Little Aguja pondweed is very difficult to identify without first drying the plants. Positive identification of Little Aguja pondweed is complicated further by its distinguishing character (basal projections) being on the fruit (instead of the more constant leaves or stems). While it seems contradictory that an aquatic plant could live in a stream that sometimes dries up, Little Aguja pondweed has developed several strategies for such a life. Not only does it produce seeds, it also has underground stems and buds that can sustain it during occasional periodic drought.