Herbs, annual or perennial, shrubs, or trees, unarmed; roots with bacterial nodules, rarely from woody rootstock. Stems erect, procumbent, or prostrate, branches usually straight, sometimes zigzag, glabrous or pubescent. Leaves alternate, even-pinnate; stipules present; petiolate; extrafloral nectaries or glandular hairs present or absent, extrafloral nectaries on petiole, sessile, subsessile, or stipitate, usually cup-shaped; leaflets 1–28(–32)[–40] pairs, blade margins usually entire, surfaces glabrous or pubescent. Inflorescences 1–10(–20)-flowered, axillary, racemes, erect; bracts present, inconspicuous; bracteoles 2, caducous or persistent at anthesis. Flowers caesalpinioid, asymmetric, enantiostylous; calyx bilateral, lobes 5, persistent; corolla yellow, petals unequal, blades narrowed to claw, claw sometimes red-spotted or orange reddish; stamens (2 or)3–10, equal or irregularly unequal; filaments glabrous, usually nearly equal to anthers; anthers basifixed, dehiscing by apical pores or short slits, lateral sutures ciliolate; ovary shortly stipitate, incurved, linear, often hairy, sometimes glabrous; style usually terminating in minute, stigmatic cavity. Fruits legumes, stipitate, flat, straight or curved, linear or linear-oblong, elastically dehiscent, coiling at dehiscence, glabrous or pubescent, often corrugated over seeds. Seeds 1–25+, obovoid-ellipsoid to rhomboid or trapezoid. x = 7, 8.

Distribution

North America, Mexico, West Indies, Central America, South America, Asia, Indian Ocean Islands (Madagascar, Seychelles), Australia.

Discussion

Species ca. 330 (12 in the flora).

Chamaecrista was segregated from the large genus Cassia and placed in subtribe Cassiinae, together with Cassia in the strict sense and Senna (H. S. Irwin and R. C. Barneby 1981, 1982). In recent molecular phylogenetic studies Cassia and Senna appear as sister taxa (B. Marazzi et al. 2006; A. Bruneau et al. 2008; Marazzi and M. J. Sanderson 2010), whereas Chamaecrista appears more distantly related and sister of the monospecific Batesia Spruce ex Bentham (Bruneau et al.). Among traditional caesalpinioids, Chamaecrista seems to be the only genus possessing rhizobial root nodules (H. D. L. Corby 1988; J. I. Sprent 2001). Flowers of Chamaecrista are asymmetric and specialized in relation to buzz pollination (pollen-collecting bees vibrate the flowers to release pollen from the anthers; G. Gottsberger and I. Silberbauer-Gottsberger 1988).

Of the six sections recognized in the current classification of Chamaecrista (H. S. Irwin and R. C. Barneby 1982), only sects. Apoucouita (H. S. Irwin & Barneby) H. S. Irwin & Barneby and Xerocalyx (Bentham) H. S. Irwin & Barneby appear as monophyletic, whereas the monospecific sect. Grimaldia (Schrank) H. S. Irwin & Barneby is embedded within sect. Absus (de Candolle ex Colladon) H. S. Irwin & Barneby, and sects. Caliciopsis H. S. Irwin & Barneby and Xerocalyx are nested within sect. Chamaecrista (A. Conceição et al. 2009). These molecular phylogenetic analyses suggest that a shift from a relatively species-poor group of rainforest trees to a more diverse and species-rich clade of savannah shrubs occurred early in the diversification history of Chamaecrista. The latter clade is composed of two ecologically and morphologically distinct main subclades (Conceição et al.). Almost 81% of Chamaecrista species occur in the Americas (G. P. Lewis et al. 2005).

In North America, Chamaecrista is represented by species of sects. Caliciopsis, Chamaecrista, and Grimaldia. All but C. greggii, a microphyllous shrub or small tree, are annual or perennial herbaceous plants. The United States represents the northern limit of the geographic distribution of Chamaecrista in the Americas.

Selected References

None.

Lower Taxa

Chamaecrista absus, Chamaecrista calycioides, Chamaecrista chamaecristoides, Chamaecrista deeringiana, Chamaecrista fasciculata, Chamaecrista flexuosa, Chamaecrista greggii, Chamaecrista lineata, Chamaecrista nictitans, Chamaecrista pilosa, Chamaecrista rotundifolia, Chamaecrista serpens

Key

1	Leaflets 1 or 2 pairs.	> 2
2	Leaflets 2 pairs; racemes terminal.	Chamaecrista absus
2	Leaflets 1 pair; racemes axillary.	Chamaecrista rotundifolia
1	Leaflets 2–28(–32)[–40] pairs.	> 3
3	Shrubs or trees, xerophytic, microphyllous; leaflets (2 or)3–5(or 6) pairs.	Chamaecrista greggii
3	Herbs, mesophytic, not microphyllous; leaflets 2–28(–32)[–40] pairs.	> 4
4	Leaflets 2–9 or (4 or)5–12 pairs.	> 5
5	Stems usually erect, rarely procumbent, regularly branched.	Chamaecrista serpens
5	Stems procumbent or prostrate, long and weakly or not branched.	> 6
6	Sepal venation parallel; leaflets (4 or)5–12 pairs; petals 5–14 mm; Texas.	Chamaecrista calycioides
6	Sepal venation reticulate; leaflets 2–5 or (5 or)6–9 pairs; petals 3.5–6.5(–7) or 11–15 mm; peninsular Florida and Florida Keys.	> 7
7	Leaflets (5 or)6–9 pairs; petals to 11–15 mm; Florida Keys.	Chamaecrista lineata
7	Leaflets 2–5 pairs; petals 3.5–6.5(–7) mm; peninsular Florida.	Chamaecrista pilosa
4	Leaflets (6–)8–28(–32)[–40] pairs.	> 8
8	Stems procumbent or prostate or mat-forming, branches straight or in zigzag pattern; on sandy plains and sand dunes of coastal Texas.	> 9
9	Pedicels 5–15 mm; stipules pale green becoming brownish or yellowish, 3+ times as long as wide; stems rarely from woody rootstock, branches usually straight.	Chamaecrista chamaecristoides
9	Pedicels 20–42 mm; stipules green, to 2 times as long as wide; stems often from horizontal, woody rootstock, branches often in zigzag pattern.	Chamaecrista flexuosa
8	Stems erect, branches usually straight; wide range of habitats.	> 10
10	Racemes usually 1(or 2)-flowered; pedicels 0.5–4[–16] mm; petals to.	> 3
3	5–8(–9)[–16] mm.	Chamaecrista nictitans
10	Racemes 1–4(or 6)-flowered; pedicels (6–)8–22(–26) mm; petals to (6–)8–23(–26) mm.	> 11
11	Roots horizontal and rhizomelike.	Chamaecrista deeringiana
11	Roots not rhizomelike.	Chamaecrista fasciculata