Horned Pondweed

Foodplant / feeds on
larva of Macroplea mutica feeds on root of Zannichellia palustris
Remarks: Other: uncertain

Outside of Europe most Zannichellia are considered to be Z. palustris (W. Van Vierssen 1982). In Europe three species have been recognized based on stamen length, fruit length, podogyne length, and the rostrum to fruit length ratio. For Z. palustris in Europe the mean rostrum length is 0.78 ± 0.20deletion} mm, the mean podogyne length is 0.4 ± 0.19 mm, and the rostrum to fruit ratio is less than 0.5 (W. Van Wierssen Vierssen 1982). North American Zannichellia does not match any of these figures exactly. In North America Zannichellia has been considered historically to comprise only one species, which has been called Z. palustris. Until further research determines the range of Zannichellia and species delimitations, we areI am continuing to consider all North American material to be monospecific and am are applying the name Z. palustris to our that material.

Leaves linear, opposite or in whorls. Peduncle of the inflorescence 1-1.5 mm long. Male and female flowers subsessile; pedicels 0.5-1 mm. style very short in flower, 2-2.5 mm in fruit; stigma peltate, wavy; achenes 2-5, stalked; stalk 1-1.5 mm long, back of the achene curved and dentate.

Herbs entirely submersed. Stems to 50 cm ´ 0.2----0.6 mm. Leaves 3.5--4.2 cm ´ 0.2--1 mm, apex acute. Staminate flowers: filament 1.5--2 mm, connective prolonged into blunt tip 0.1 mm. Pistillate flowers: pistils 4--5; style 0.4--0.7 mm. Fruits 1.7--2.8 ´ 0.6--0.9 mm; rostrum 0.7--2 mm; podogyne 0.1--1.5 mm; pedicel 0.3--1.2 mm.

Distribution: A cosmopolitan species.

Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ala., Alaska, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico; West Indies; Central America; South America; Eurasia; Africa; Australia.

Fl. Per. February-March.

Flowering spring--summer.

Brackish or fresh waters of streams, lakes, or estuaries; 0--2900m.

Zannichellia palustris L. Sp. PL 969. 1753
Zannichellia intermedia Torr.; Beck, Bot. 385. 1833.
Stems slender, simple or branched ; leaves all submerged, linear, capillary, 2-10 cm. long, acute or almost pungent at the apex, 1-nerved ; stipules scarious, free from the leafbases, scarcely 2 cm. long; staminate and pistillate flowers in the same leaf -axil, subtended or enclosed by a hyaline bract ; staminate flower of a single 2-celled anther on a slender filament ; pistillate flowers of 2-10 carpels, sessile at first, often pedicellate after anthesis ; carpels flask-shaped, ribbed or toothed on the margins, or sometimes smooth ; style recurved, persistent; stigma cup-shaped, with dentate or angled edges; mature fruit 2-4 mm. long, rarely pitted.
Type locality : Kurope.
Distribution ; In fresh or brackish water nearly throughout North America, except the
extreme north.

Zannichellia palustris, the horned pondweed, is a plant found in fresh to brackish waters in the United States (especially in the Chesapeake Bay), Europe, Asia, Australasia, and South America. It is recognizable by its long, thread like leaves, and "stringy" appearance. Its roots are also long and tendril-like, and its seeds bear a distinctive horned shape, hence the common name. The species epithet palustris is Latin for "of the marsh" and indicates its common habitat. A diploid, its chromosome number was confirmed as 2n = 24.