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common poolmat, horned-pondweed

Habit Herbs entirely submersed.

to 50 cm × 0.2–0.6 mm.


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.


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.

Zannichellia palustris

Phenology Flowering spring–summer.
Habitat Brackish or fresh waters of streams, lakes, or estuaries
Elevation 0–2900 m (0–9500 ft)
from FNA
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; Mexico; Central America; South America; West Indies; Eurasia; Africa; Australia
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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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 22.
Parent taxa Zannichelliaceae > Zannichellia
Name authority Linnaeus: Sp. Pl. 2: 969. (1753)
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