Cassia zygophylloides

Title

Cassia zygophylloides

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Cassia zygophylloides Taub.

Description

152.  Cassia zygophylloides Taubert in Flora (Regensb.) 75: 79. 1892.

Slender, repeatedly ramified shrubs or treelets 1-4 (5) m, with longitudinally striped older stems and trunks, the densely leafy branchlets of the year like the lf-stalks and axes of inflorescence at least thinly, often densely hispidulous with glandular setules up to 0.25-0.5 mm, sometimes in addition variably villosulous, the thin-textured, bicolored lfts eglandular but quite variably pubescent, almost always pilosulous dorsally at base, especially along the distal side of midrib near and often on the pulvinule, less often thinly pilosulous overall, above commonly glabrous but sometimes pilosulous, the sessile or very shortly pedunculate racemes terminal to all the branchlets, either shortly few-fld and sub-immersed in foliage or elongately many-fld and far-exserted, then sometimes incipiently paniculate-branched.

Stipules erect, firm, subulate to triangular-subulate, 0.6-1.6(-2) mm, commonly nigrescent at apex, persistent.

Lvs loosely ascending and widely spreading, slender-petiolulate, 2-6.5(-7) cm; pulvinus ovoid slightly dilated, pallid or discolored, (0.4-)0.6-1.8 mm; petiole very slender, (11 -) 14-38 mm, mostly 1.5—3 times as long as the lower pair of lfts, at middle (0.25-)0.3-0.4 mm diam, very narrowly winged and grooved; rachis 1.5-7(-10) mm; lfts 2 pairs, displayed as other Absoideae, on linear or slightly dilated, when dry wrinkled, almost always pilosulous pulvinule 0.7-1.4 mm, the distal pair a little larger, in outline commonly obovate and broadly to shallowly emarginate, rarely narrowly obovate, exceptionally elliptic, muticous or minutely mucronulate, (7-)9-30(-33) x 4-16(-22) mm, the entire, glabrous or thinly ciliolate margin either plane or in age revolute, at base asymmetrically rounded or on proximal side subcordate, the blades membranous or thinly chartaceous, above dull olivaceous, beneath almost always paler and often faintly pinkish- mottled, varying from villosulous overall on both sides to glabrous except for a patch of hairs near midrib just above pulvinule on lower side, the slender midrib with (3-)4-6 pairs of secondary and often some connecting tertiary venules either all above immersed and prominulous beneath, or all the venation equally prominulous on both faces.

Racemes terminal to leafy branchlets, shortly pedunculate or rarely sessile, (3-)5-65-fld, becoming 1-20 cm, the 1-3 simultaneously expanded fls raised in shorter racemes almost to level of the corymbose unopened buds, in longer ones standing far beneath the racemose buds; bracts deltate to triangular-subulate, 0.8—1.6 mm, persistent; pedicels ascending, (5-)6-17(-19) mm, bracteolate (2-)3-8(-11) mm below calyx; bracteoles resembling bracts, little smaller; buds sub- globose, rarely ovoid, always obtuse, either glabrous, thinly setulose, or densely villosulous, the villous pubescence rarely yellowish; sepals submembranous, pallid greenish or purple-tinged, 5-8.5 mm, the outer ones elliptic-oblanceolate, the inner obovate, 2.2-3.7 mm wide, all obtuse; petals yellow, the four plane ones varying from obovate-cuneate to broadly oblanceolate, of unequal size, usually 2 larger and 2 smaller, the longest up to 8-15(-16) x (4.5-)5-8 mm, the fifth ±as long, coiled; ovary either setulose or glabrous; ovules 4-7(8).

Pod 2.2-3.8(-4) x (0.5-)0.55-0.8 cm, the castaneous or purplish valves both villosulous and setulose or glabrous and lustrous; seeds atrocastaneous, 3.5-4.8 x 2.5-3.1 mm, not highly lustrous, lineolate.

In form of the leaves, with a very slender, proportionately long petiole bearing near tip two crowded pairs of small, ordinarily obovate leaflets, C. zygophylloides resembles most nearly the procumbent herb C. fagonioides, but is erect and shrubby or even arborescent, notable for the longitudinally striped bark of the old trunks and branchlets, and has yellow, not orange flowers. It differs from the partly sympatric C. viscosa, also shrubby but less intricately branched, in the long-petiolate, less viscous leaves, and from the more closely related C. brevicalyx, similar as to the foliage, in the smaller flowers. In its vast discontinuous range extending from near 19° N in Puebla, Mexico to 17° S in eastern Brazil, C. zygophylloides is represented by numerous, mutually isolated populations that differ between themselves in pubescence of foliage and inflorescence, in length of raceme, in size of flower, and in pubescence of pod. The type of C. zygophylloides itself, from Minas Gerais, a densely pubescent plant with far-exserted racemes of many small flowers already racemosely elongate when in bud, and that of C. enneandra, from Oaxaca, which is glabrate, with subcorymbiform racemes of few, larger flowers immersed in foliage, are so different that direct comparison suggests two perfectly distinct specific lines. These extreme forms are, however, linked by a series of intermediate ones in which states of pubescence, flower-sizes and inflorescences of varying vigor appear in all possible combinations. The small taxonomic value that can be attached to leaf-pubescence in this species is demonstrated by a single collection (Irwin & al. 23185) of var. zygophylloides from Minas Gerais, in some plants of which the leaflets are densely villosulous dorsally and thinly so ventrally, but in others glabrous except for a little tuft of hairs in one basal angle of the midrib beneath, a pubescence pattern that recurs here and there northward into Mexico. A less forceful but significant example is furnished by two collections (Irwin & at. 30731, 32651) of var. colligans from Serra do Tombador in central Bahia, obviously conspecific in the narrowest sense but the first glabrate with some far-exserted racemes, the latter densely and softly hairy but with all racemes abbreviate and few-flowered.

While pubescence of the leaves and length of raceme, which contribute much to the facies of the individual plant or population, have little practical taxonomic significance in C. zygophylloides, a species obviously genetically plastic in these features, it is otherwise with flower-size and vesture of the pod. The populations north of the Amazon River have relatively large flowers in comparison with those of eastern Brazil. In each group as delimited by flower-size and dispersal there are geographically and probably ecologically segregated forms with glabrous and pubescent pods. Pronounced leaf-pubescence combined with elongate racemes occurs only in the southern, small-flowered group; glabrate foliage and short racemes occur together in both areas but are common together only northward. Using these criteria it is possible to distinguish within C. zygophylloides four geographic varieties:

Key to varieties of C. zygophylloides

1. Fl relatively small, the longer petals 8-11 (-12) mm; racemes commonly many-fld and laxly elongate, the unopened buds usually but not consistently racemose; e. Brazil, s.-ward from Ceara.

2. Ovary and pod villosulous and viscid-setulose; buds consistently racemose; Minas Gerais and Bahia.

152a. var. zygophylloides

2. Ovary and pod glabrous; buds either racemose or subcorymbose; centr. Bahia n. to Ceara.

152b. var. colligans

1. Fl larger, the longer petals 12-15(-16) mm (if exceptionally only 10—12 mm the raceme depauperate, immersed, and the unopened buds corymbose); Guayana (Terr. Roraima, Brazil, and adjacent interior Guyana (British Guiana); lower Orinoco valley, Venezuela) to s. Mexico.

3. Ovary and pod villosulous and viscid-setulose; inland and upland Guayana and disjunctly in centr. America (Honduras, British Honduras, Guatemala, s.-e. Mexico).

152c. var. deamii

3. Ovary and pod glabrous (sometimes a few hairs along sutures but the faces of the valves lustrously glutinous and smooth); coastal chaparral below 30 m in Sucre, Venezuela.

152d. var. caribaea