Chamaecrista serpens

Title

Chamaecrista serpens

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Chamaecrista serpens (L.) Greene

Description

26. Chamaecrista serpens (Linnaeus) Greene, Pittonia 4: 29. 1899. Cassia serpens Linnaeus, Syst. ed. 10, 1018. 1759.—Typus infra sub var. serpenti indicatur.

Slender herbs with several or many pliantly humifuse (exceptionally assurgent), simple or sparingly branched stems radiating from the crown of a blackish taproot or ultimately (especially in arid climate) a weakly suffruticulose caudex, commonly both puberulent with short incurved hairs and hispid with at least a few, sometimes with many fine divaricate septate setae up to (0.5-)0.8-1.4(-1.8) mm, the incurved hairs often aligned in vertical strips along stem and pedicel, the latter often concentrated on the petiole, but sometimes extending to stipule- and lft-margins, the stems, and dorsal face of lfts (or to some of these), but sometimes wholly lacking, the pod often likewise both puberulent and pilose with yet longer, ± flexuous filamentous hairs, but sometimes only puberulent, the usually thin- textured lfts either concolorous dull olivaceous or olivaceous above and cinnamon-brown beneath.

Stipules erect, subappressed to stem, narrowly lanceolate to narrowly ovate- acuminate or -caudate, (1.5-)2-7 x (0.2-)0.3-1.2 mm, the submembranous persistent blades 3-7(-9)-nerved from pulvinule, at base slightly oblique or (var. oaxacana) incipiently semicordate.

Lvs divaricate or ascending, commonly displayed horizontal to the meridian (7-) 10—35(-42) mm, short-petiolate, the expanded blade ovate in outline; petiole (including wrinkled pulvinus) 1.5-4 mm, narrowly sulcate ventrally, in profile 0.2-0.8 mm wide; gland situated near middle of petiole proper, discoid or cupulate, usually reddish, 0.2—0.5 mm diam, elevated on a stipe 0.2—1.1(—1.4) mm, sometimes accompanied by a second smaller petiolar gland, and exceptionally by1-2 yet smaller on rachis; rachis (3-)5-26(-30) mm; lfts 3—9(-12), of some adult lvs at least 4 pairs, the middle usually slightly largest, in outline narrowly oblong to oblong-oblanceolate, dimidiately narrow-obovate, or obliquely obovate, obtuse or deltately acute, mucronulate or aristate by excurrent costa, 3—12(—14) x 0.4-6.3 mm, at base auriculate on proximal side, straight or slightly falcate, the submembranous or less often firmly chartaceous blades commonly glabrous on both faces, sometimes setose beneath, the margin glabrous, minutely ciliolate, or erratically setose, the displaced midrib with, on its broader side, 2-3(-4) primary veins palmately ascending from pulvinule and on the narrow side 3-4 weak secondary pinnate venules all finely or (adult) coarsely sharply prominulous on both faces, sometimes when young subimmersed.

Peduncles axillary, up to 1 (— 1.5) mm, l(-2)-fld; pedicels at anthesis ascending toward meridian, subfiliform or very slender, in fruit a little thickened and commonly divaricate or deflexed and geniculate under the pod, 1.2-4(-4.5) cm, glabrous or puberulent; bracteoles above middle of pedicel, lanceolate to narrowly ovate, 0.8-2.5 mm; buds ovoid-acuminate, glabrous or thinly setose; sepals membranous, pallid or greenish seldom tinged with red or yellow, the longer ones lanceolate or ovate-acuminate, 3—12(—13.5) mm; petals yellow, at anthesis expanded into a campanulate but highly asymmetrical perianth, the 3 adaxial ones smallest, oblanceolate to narrowly obovate, a little shorter to a little longer than the sepals, the 2 abaxial longer, one of them resembling the 3 adaxial in outline, the other broadly falcate-obovate, 5-19(-20) mm, its distal margin incurved but not concealing the androecium; stamens 10, the 5 oppositisepalous larger than the reduced inner whorl, the yellow anthers all subsessile, the longest 2.5-9.5 mm; style varying in length with petals and stamens, 2-10 mm; ovary often both strigulose and pilose with weak ascending hairs, but the latter sometimes few or 0; ovules 3— 10(— 12).

Pod linear-oblong, short-stipitate, 14-40(-45) x 3-5 mm, the pale green or reddish valves ripening stramineous, castaneous, or ultimately dark brown, at once incurved-puberulent and pilose with fine flexuous hairs to 1.5—3 mm, or the latter wanting; seeds compressed-pyriform or prismatic, 2.3—3(—3.3) mm, the testa dull, pale or dark brown, lineolate with crateriform pits usually appearing as small dark, pale-centered rings, mucilaginous when wetted.

In the foregoing description of Ch. serpens we have extended the concept of Bentham (1870, p. 162) so far as to admit two or three more pairs of leaflets to the average adult leaf and a corolla slightly larger than that of the already relatively large-flowered var. grandiflora. As redefined, the species accommodates at one extreme the small-flowered Jamaican plant to which the epithet was originally applied and on the other a series of forms progressively larger-flowered that culminates in the Mexican entities that have passed recently as Cassia wrightii, C. palmeri and segregates from these. In habit Ch. serpens resembles the related and partly sympatric Ch. pilosa, a usually more coarsely leafy and, in the common range, more hispid plant that is, however, most reliably distinguished by the pentandrous androecium. The also related Ch. trichopoda, which where sympatric with var. serpens is similar in flower size, will be readily recognized by its many (11+ not 3-8) pairs of leaflets.

Conspicuous variation within Ch. serpens follows two independent modes, one trichotic, the other floral. The double vesture of short incurved and long septate setose hairs characteristic of the group is present at least potentially in all forms of the species, but the proportions of the two sorts of hair, the relative and absolute density and length of each, and the extent to which setae extend outward from the petiole, where most prevalent, to the stem, stipules, leaflets and sepals are too often subject to erratic modification to serve as taxonomic characters. It is otherwise with flower-size, which appears generally to have strong correlation with geographic dispersal patterns, and is furthermore linked to some degree with minor traits of foliage and even pubescence. The large-flowered varieties appear to have arisen independently in North and South America, and have acquired the greatest substance near and outside the Tropic lines in southern Paraguay and adjoining Argentina (var. grandiflora), and in northwest Mexico (var. wrightii). Each is tied in to the matrix of small-flowered tropical forms by sympatric or vicariant types of intermediate flower-size which they resemble more closely in minor characters of foliage than they do races of comparable flower-size in the opposing hemisphere.

A unicate specimen from Yhú in southeastern Paraguay (Hassler 9531, G) strongly suggests a hybrid Ch. serpens x rotundifolia, the 3-4 pairs of leaflets being fewer and broader than elsewhere in Ch. serpens, but obviously different from the single broad pair of Ch. rotundifolia. The intermediate flower size might have been derived from combination of the typical variety of either species with the var. grandiflora of the other.