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Published In: Methodus Plantas Horti Botanici et Agri Marburgensis : a staminum situ describendi 272. 1794. (4 May 1794) (Methodus) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

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2. Chamaecrista (L.) Moench

Plants annual (perennial herbs or woody elsewhere), unarmed, with 1 to few stems; root nodules present. Leaves short- to long-petiolate, the petiole with a relatively large, sessile or stalked, more or less cup-shaped gland. Stipules well developed, with several prominent, more or less parallel, raised veins, persistent. Leaf blades evenly 1 time pinnately compound. Leaflets numerous, opposite, oblong to narrowly oblong or oblong-elliptic, asymmetrical at the base, the midvein usually somewhat off-center, the margins entire. Inflorescences axillary or lateral from just above the leaf axil, appearing as solitary flowers or small, loose clusters (actually short racemes), the flower stalks with 2 small bracts near or above middle, often twisted 180° so that the flower is resupinate. Flowers perfect, perigynous, somewhat asymmetrical. Hypanthium short, saucer-shaped. Calyces of 5 free sepals. Corollas of 5 free petals, these dissimilar in size and shape, the largest one appearing lowermost in the flower, yellow (rarely white), sometimes reddish-tinged toward the base. Stamens 5 or 10, usually all fertile, the filaments short, not fused, the anthers of different lengths, attached at the base, dehiscing by apical slits or pores. Styles curved. Fruits legumes, narrowly oblong, straight to curved, not twisted, strongly flattened, with 4–20 seeds, elastically dehiscent with coiling valves. Seeds nearly square to trapezoidal in outline, flattened, light to dark brown; pleurogram absent. About 265 species, widespread, primarily in the American tropics and temperate regions.

Although long recognized as a natural group, the generic status of Chamaecrista has been debated for over 200 years. Chamaecrista and Senna often have been included in the large genus Cassia, which in its broadest sense contains more than 600 species and is the largest genus in Caesalpinioideae (Isely, 1975; Irwin and Barneby, 1976). Bentham (1871) recognized 3 subgenera that correspond more or less to Cassia in the narrow sense, Senna, and Chamaecrista. Irwin and Barneby (1981, 1982) provided a discrete set of characters for recognizing these at the generic level and made the required nomenclatural changes. In this narrow sense, Cassia consists of only 30 species of trees and shrubs that are confined to the tropics, lack extrafloral nectaries, have very long, sigmoidally curved filaments, and have anthers that dehisce by slits or basal pores. In contrast, both Chamaecrista and Senna are large genera, each with over 250 species of trees, shrubs, and herbs. Their stamens have very short filaments and dimorphic or trimorphic anthers that dehisce by terminal slits or pores. Chamaecrista is distinguished from Senna by the large, persistent stipules, 2 small bracts on the flower stalk, elastically dehiscent legumes, stamens with usually 2 sizes of anthers, and seeds lacking a pleurogram. Senna lacks bracts on the flower stalk, has tardily dehiscent, nonelastic legumes, a graded series of anthers, and seeds with a distinctive pleurogram appearing as a depressed area. Furthermore, root nodules with nitrogen-fixing bacteria are found in Chamaecrista, but not in Senna or the majority of other Caesalpinioideae.

The leaflets of Chamaecrista are somewhat sensitive to the touch, although not as sensitive as those of certain taxa of Mimosoideae. Uprooting the plant also causes the leaflets to close, and herbarium specimens almost always have the leaves in the closed position. On their own, the leaves close and pull upward at night into a so-called sleeping position, a phenomenon known as nyctinasty, common to many Fabaceae. This movement is thought to control water loss or afford protection from herbivores.

The seed dispersal mechanism is also interesting. When the seeds are fully mature and the legume is dry, the two valves separate suddenly, flinging the seeds a meter or more away (Lee, 1984).

The two Missouri species of Chamaecrista, particularly the more abundant C. fasciculata, are important wildlife food plants and sometimes are planted for this purpose. The foliage is nutritious for deer and livestock, although it contains anthraquinone compounds that can cause irritation of the digestive tract if eaten in large quantities (Burrows and Tyrl, 2001). Birds (especially quail and turkey) are fond of the seeds.

 

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1 1. Stems 6090 cm tall, unbranched or few-branched near or above middle; flower stalks 1015 mm long; flowers showy, 2530 mm in diameter, the petals subequal, the largest petal only slightly larger than the others; stamens 10, the anthers 610 mm long ... 1. C. FASCICULATA

Chamaecrista fasciculata
2 1. Stems 3040 cm tall, usually few-branched toward the base; flower stalks 23 mm long; flowers inconspicuous, 810 mm in diameter, the petals strongly dimorphic, the largest petal almost twice the size of other petals; stamens 5, the anthers 23 mm long ... 2. C. NICTITANS Chamaecrista nictitans
 
 
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