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Roemer senna, twoleaf senna, twoleaf wild sensitive plant

coffee senna, septicweed

Habit Herbs, perennial, to 0.7 m. Leaves slightly sclerophyllous, 2.5–9.5 cm, hairy; stipules caducous; extrafloral nectary 1, between leaflet pair, shortly stipitate; leaflet pairs 1, blades lanceolate-oblong or lanceolate, 20–70 × 4–14 mm. Herbs, perennial, bushy, to 2.2 m; branches dark green and blackish.
Leaves

mesophyllous, 11–26 cm, glabrous or glabrate;

stipules caducous;

extrafloral nectary 1, base of petiole, sessile or subsessile;

leaflet pairs 4 or 5(or 6), blades lanceolate- or ovate-acuminate, 45–100 × 12–38 mm.

Racemes

1–5-flowered;

bracts caducous.

usually (1 or)2–5-flowered;

bracts caducous, longer than bud, often blackish green.

Pedicels

9–16 mm.

8–21 mm.

Flowers

monosymmetric;

calyx caducous, pale green;

corolla yellow or orange-yellow, longest petal 12–17 mm;

androecium not heterantherous, stamens 7, staminodes 3;

anthers 2.2–3.3 mm, dehiscing by 1 apical pore, apical appendage 0;

gynoecium nearly linear, ovules 22–40;

ovary densely hairy;

style slightly incurved.

monosymmetric;

calyx pinkish or fuscous;

corolla yellow, longest petal 12–17 mm;

androecium heterantherous, stamens 6, staminodes 3 + 1;

anthers of middle stamens 3.2–5.2 mm, of abaxial stamens 4.9–6.6 mm, elongated beyond pores, dehiscing by U-shaped pore, apical appendage linguiform, thickened;

gynoecium incurved, ovules 40–60;

ovary densely hairy;

style slightly incurved.

Legumes

erect, subcylindrical, straight or slightly curved, 20–35 × 4.5–6.5 mm, corrugated over seeds, dehiscing apically downward.

ascending, flat, slightly curved or straight, linear, 80–135 × 6.5–9.5 mm, corrugated over seeds, dehiscent.

Seeds

brown or pinkish brown, paddle-shaped or pyriform.

olive green or brownish, obovoid.

2n

= 28.

= 26, 28.

Senna roemeriana

Senna occidentalis

Phenology Flowering spring–early fall. Flowering mid summer–early winter.
Habitat Mesquite grasslands, chaparral, draws in shortgrass prairies, barren hillsides, desert washes, roadsides. Disturbed habitats, waste places, roadsides.
Elevation 100–2000 m. (300–6600 ft.) 0–1200 m. (0–3900 ft.)
Distribution
from FNA
NM; OK; TX; Mexico (Chihuahua, Coahuila, Nuevo León)
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; FL; GA; IA; IL; IN; KS; LA; MA; MD; MO; MS; NC; NY; OK; SC; TN; TX; VA; Mexico; Central America; South America; West Indies [Introduced in North America; introduced also in tropical and subtropical Eurasia, Africa, Australia]
[WildflowerSearch map]
[BONAP county map]
Discussion

Although Senna occidentalis is probably native to the tropical New World, the species is now weedy in so many countries worldwide, including also other parts of the New World, that the exact range of its geographic distribution as a native is a matter of speculation (H. S. Irwin and R. C. Barneby 1982). In the flora area, it is considered as naturalized (R. Kral et al. 2012; R.

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

Source FNA vol. 11. FNA vol. 11.
Parent taxa Fabaceae > subfam. Caesalpinioideae (excluding Mimosoid clade) > Senna Fabaceae > subfam. Caesalpinioideae (excluding Mimosoid clade) > Senna
Sibling taxa
S. alata, S. armata, S. artemisioides, S. atomaria, S. bauhinioides, S. corymbosa, S. covesii, S. durangensis, S. hebecarpa, S. hirsuta, S. ligustrina, S. lindheimeriana, S. marilandica, S. mexicana, S. multiglandulosa, S. obtusifolia, S. occidentalis, S. orcuttii, S. pendula, S. pilosior, S. pumilio, S. ripleyana, S. surattensis, S. wislizeni
S. alata, S. armata, S. artemisioides, S. atomaria, S. bauhinioides, S. corymbosa, S. covesii, S. durangensis, S. hebecarpa, S. hirsuta, S. ligustrina, S. lindheimeriana, S. marilandica, S. mexicana, S. multiglandulosa, S. obtusifolia, S. orcuttii, S. pendula, S. pilosior, S. pumilio, S. ripleyana, S. roemeriana, S. surattensis, S. wislizeni
Synonyms Cassia roemeriana, Earleocassia roemeriana Cassia occidentalis, Ditremexa occidentalis
Name authority (Scheele) H. S. Irwin & Barneby: Mem. New York Bot. Gard. 35: 282. (1982) (Linnaeus) Link: Handbuch 2: 140. (1829)
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