The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

sessile joyweed

alligator weed, pig weed

Habit Herbs, annual or perennial, 2–6 dm. Herbs, perennial, aquatic to semiterrestrial, stoloniferous, to 50 dm.
Stems

procumbent, pubescent in lines, glabrate.

prostrate, forming mats, often fistulose, glabrous.

Leaves

sessile;

blade elliptic to oblong or oblanceolate, 1.2–5 × 0.5–2.2 cm, apex obtuse to acute, glabrous.

sessile;

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

Inflorescences

axillary, sessile;

heads white, subglobose or ovoid, 0.5–1.1 cm;

bracts keeled, ca. 1/2 as long as tepals.

terminal and axillary, pedunculate;

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

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

Flowers

tepals white, ovate to lanceolate, 2–3.5 mm, apex acuminate, hairs not barbed;

stamens 5;

anthers 3–5, globose;

pseudostaminodes subulate, margins laciniate.

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

stamens 5;

pseudostaminodes ligulate.

Seeds

lenticular, 0.9–1.1 mm.

not seen.

Utricles

included within tepals, sides exerted in mature fruit, greenish stramineous, obcordate, 1.3–1.7 mm, apex retuse.

not seen.

Alternanthera sessilis

Alternanthera philoxeroides

Phenology Flowering summer–early fall. Flowering early spring–summer.
Habitat Wet disturbed areas Ponds, ditches, streams, bayous
Elevation 0-20 m (0-100 ft) 0-200 m (0-700 ft)
Distribution
from USDA
Mexico; South America; West Indies; Central America (Belize, Costa Rica, Guatemala, Nicaragua, Panama); Africa; Asia [Introduced, Ala., Fla., Ga., La.]
[WildflowerSearch map]
[BONAP county map]
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]
[WildflowerSearch map]
[BONAP county map]
Discussion

Alternanthera sessilis is reported from Maryland, Mississippi, South Carolina, and Texas, but I have seen no specimens from these states.

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

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. 450. FNA vol. 4, p. 448.
Parent taxa Amaranthaceae > Alternanthera Amaranthaceae > Alternanthera
Sibling taxa
A. brasiliana, A. caracasana, A. ficoidea, A. flavescens, A. maritima, A. paronychioides, A. philoxeroides, A. pungens
A. brasiliana, A. caracasana, A. ficoidea, A. flavescens, A. maritima, A. paronychioides, A. pungens, A. sessilis
Synonyms Gomphrena sessilis Bucholzia philoxeroides, Achyranthes philoxeroides
Name authority (Linnaeus) R. Brown ex de Candolle: Cat. Pl. Hort. Monsp., 77. (1813) (Martius) Grisebach: Abh. Königl. Ges. Wiss. Göttingen 24: 36. (1879)
Web links