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alligator weed, pig weed

Habit Herbs, perennial, aquatic to semiterrestrial, stoloniferous, to 50 dm.

prostrate, forming mats, often fistulose, glabrous.



blade narrowly elliptic, elliptic, or oblanceolate, 3.5–7.1 × 0.5–2 cm, herbaceous, apex acute to obtuse, glabrous.


terminal and axillary, pedunculate;

heads white, globose, 1.4–1.7 cm diam.;

bracts not keeled, less than 1/2 as long as tepals.


tepals monomorphic, white, lanceolate or oblong, 6 mm, apex acute, glabrous;

stamens 5;

pseudostaminodes ligulate.


not seen.


not seen.

Alternanthera philoxeroides

Phenology Flowering early spring–summer.
Habitat Ponds, ditches, streams, bayous
Elevation 0-200 m (0-700 ft)
from FNA
AL; AR; CA; FL; GA; IL; KY; LA; MS; NC; SC; TN; TX; VA; West Indies; native to South America [Introduced in North America]
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[BONAP county map]

Alternanthera philoxerioides is said to reproduce only vegetatively in North America. I have seen no fruit or seed.

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

Source FNA vol. 4, p. 448.
Parent taxa Amaranthaceae > Alternanthera
Sibling taxa
A. brasiliana, A. caracasana, A. ficoidea, A. flavescens, A. maritima, A. paronychioides, A. pungens, A. sessilis
Synonyms Bucholzia philoxeroides, Achyranthes philoxeroides
Name authority (Martius) Grisebach: Abh. Königl. Ges. Wiss. Göttingen 24: 36. (1879)
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