Chamaecrista kunthiana

Cassia kunthiana sensu Vogel, 1837, p. 57.

Cassia tagera sensu Bentham, 1870, p. 162; 1871, p. 570; auct. plur. recentior. Chamaecrista tagera sensu Britton & Rose, 1930, p. 276. Non Cassia tagera Linnaeus, nom. confus.; cf. Irwin & Barneby, Brittonia 28(4): 436. 1976.

Perennial herbs from blackish, white-tipped, often richly nodular roots, the many slender pliant, freely branching stems humifusely radiating from the root- crown or in age from a shortly branched, weakly suffruticulose caudex, forming dense mats of small foliage (l-)2—11 dm diam, either subglabrous below the always basally hispidulous calyx and puberulent ovary to thinly pilosulous and setose with fine spreading septate hairs to 0.7-1.6 mm, the pilosulous vesture of incurved short hairs often reduced to a minute puberulence along the ventral side of the petioles, the pedicels, or the stem (in lines), the setae confined mostly to the dorsal side of petiole, the margins of stipules and lfts, rarely extending to the lower face of lfts, the herbage green concolorous, the small flowers raised from the mat of foliage on filiform pedicels, the perianth little expanded even at sunrise, closing by noon.

Stipules erect, appressed to stem, persistent, broadly lance- or ovate-acuminate from symmetrically cordate-auriculate base, (2—)3—10(—11) x (0.7-) 1-4.5 mm, the blades membranous becoming hyaline, prominently (7-)9-15-nerved from base, the nerves all passing distally into a strong marginal one, the central nerve produced as a spinule, the faces usually glabrous, the margin either glabrous or thinly setose.

Lvs 5-17(-20) mm, the expanded blade 6-foliolate subcircular or broadly flabellate and longer than the abbreviated rachis; petiole including wrinkled pulvinus (2-)2.5-6 mm, at middle 0.3-0.5 mm diam, openly grooved ventrally; gland situated near or above middle of petiole, urceolate, the head 0.2-0.4 mm diam, the slender stalk 0.25-0.6 mm, at least as long as the head’s diam; rachis (1-) 1.5-3 mm, dilated under each lft; lfts 3 pairs, by day displayed face upward, the proximal pair directed backward, the median pair horizontally divaricate, the distal (and widest) pair forward, in sleep (or wilted, as in most spms) all forwardly imbricated, in outline dimidiately obovate, obtuse or deltately acuminate, mucronulate by the excurrent, strongly displaced midrib, at base cuneate on the distal and shallowly auriculate on the proximal side, the distal pair 3—10(—12) x (1.5—)2—5(—6) mm, the rest usually at once a little shorter and narrower, the proximal pair sometimes dimidiately oblanceolate, the wider ones palmately 2- the narrower 1-nerved from base on proximal side of midrib, these primary veins with few pinnate venules prominulous on both faces but beneath more sharply so and usually pallid.

Peduncles exactly axillary, up to 1 mm, l(-2)-fld; pedicels at anthesis filiform, incurved under calyx, firmer in fruit, (3-)5-30(-34) mm; bracteoles linear-lanceolate or subulate, 1.3-3.3 mm; buds ovoid-acuminate, horizontally spreading, glabrous beyond the usually hispidulous base; sepals green or brownish-red, ovate- or broadly lance-acuminate, the longest 3—4.2 mm; petals yellow, at full anthesis forming a subglobose perianth (never widely opening), 4 obovate-cuneate of somewhat unequal length, the 2 adaxial slightly larger, up to 3.5—5 mm, the fifth very obliquely obovate, broader than the rest but scarcely longer, incurved over the androecium and gynoecium; stamens 5-7, heteromorphic, 2-3 adaxial with short oblong anthers borne on a slender filament ± as along as themselves, 1 abaxial, borne on a short stout filament, 2—3 variably degenerate or fully sterile, sometimes reduced to a linear rudiment; gynoecium only slightly askew, ovary appressed-strigulose or spreading-hispidulous; style linear, 1—1.9 mm, incurved distally; ovules l-4(-5).

Pod horizontal or declined, minutely stipitate, the body oblong (when 1-seeded ovate) in outline, (4-)7-12(-15) x 3-4.5(-5) mm, the brown, ultimately nigrescent valves finely strigulose or pilosulous; seeds irregularly obtusely rhomboid, 2.2-3.1 (—3.6) mm, the testa light brown or ochraceous dull, faintly lustrous-pitted, with faint fuscous transverse line at distal end, filamentous when moist. Collections: 163.

Savannas, llanos, campos, glades in pineforest (Centr. Amer.) and cerrado (Brazil), often in sandy or disturbed soils, an abundant and successful weed of waysides and fallow fields, and of pastures where resistant to browsing and forming part of the sod, mostly below 600 m but ascending in Mexico (Veracruz) to 1000, in Honduras to 1200, in Panama to 1500, and in the Brazilian Plateau (Goiás) to 1150 m, discontinuously dispersed to the n. and s. of the Amazonian Hylaea: s. Mexico (Guerrero to Veracruz and Chiapas, e. into Yucatan Peninsula) and w. Cuba (Isla de Pinos) s. through Central America to Panama; middle Orinoco valley, upstream from Parmana, in Guárico and Bolívar, Venezuela and adjoining Vichada, Colombia, to headwaters of Rio Negro in Amazonas, Brazil; Brazilian Planalto from Tocantins valley in n. Goiás and adjoining Maranhão s. through Goiás, extreme w. Bahia and Distrito Federal to the Triângulo of w. Minas Gerais, thence w. through s. Mato Grosso into Santa Cruz, Bolivia; sometimes cultivated, as at Belém (Pará) from seed collected on upper Rio Negro.—Fl. both n. and s. of the equator primarily at end of the rainy season and onward, but in lowlands irregularly throughout the year.—Golondrina (Ven.).

A species readily recognized by its prostrate, mat-forming habit of growth and especially by the small, sensitive, 6-foliolate leaves. The six leaflets, densely set along a very short rachis, form when expanded a blade of broadly fan-shaped or almost circular outline, face upward to the meridian, but in sleep or when wilted (as in most herbarium specimens) fold forwardly together, face to face, each pair clasping that next above it. The small fleeting flower, which generally fades by noon of the day it opens, is well suited to autogamous fertilization, the reproductive organs of both sexes being enclosed together within the sac of the larger incurved fifth petal. As would be expected, a fertile pod is produced by virtually every flower.

The variable vesture of Ch. kunthiana is of the double type common to many chamaecristas, composed of short incurved hairs and fine spreading septate setae. In Mexico, Cuba, and Central America southward to Belize and El Salvador the average plant appears almost glabrous, setae being absent or nearly so, and the stem, ventral margins of the petiole and pedicels are alone thinly puberulent. From Nicaragua southward and in the Orinoco valley setae appear regularly on the dorsal keel of the petiole, or along margins of some upper stipules and leaflets, or on some of these, occasionally extending to the dorsal face of the leaflets. North of the Amazon the ovary and pod are strigulose with subappressed hairs, but in southeastern Brazil, where the vesture of the stems and foliage is essentially that of southern Central America, the ovary is densely hispidulous and the pod that ripens from it is loosely pilose. The correlation between vesture and dispersal is, however, imperfect, two forms occurring occasionally together and the few collections known from Bolivia being of the glabrate type. A slight variation in flower-size appears to occur sporadically through the range of the species, which is in other respects variable only in stature and amplitude of leaflets, subject to influence of habitat, age and season. ’

In Panama (La Jagua, prov. Panamá) Dr. J. A. Duke observed leaf-cutter ants of the genus Atta carrying away leaves and especially flowers of Ch. kunthiana, presumably for use in their subterranean nurseries.