Cassia orbiculata Benth.

Authors

Howard S. Irwin, Rupert C. Barneby

Authority

Irwin, Howard S. & Barneby, Rupert C. 1978. Monographic studies in Cassia (Leguminosae, Caesalpinioideae). III. Sections Absus and Grimaldia. Mem. New York Bot. Gard. 30: 1-300.

Family

Caesalpiniaceae

Scientific Name

Cassia orbiculata Benth.

Type

Typus infra sub var. orbiculata indicatur.

Synonyms

Cassia orbiculata Benth. var. orbiculata

Description

Species Description - Shrubs and small trees highly variable in stature and pubescence, at anthesis 0.5-4 m tall, the fruticose forms either diffuse or bushily rounded, the treelets with crooked trunks and amply rounded head of foliage, the older branchlets thickened and corky, abruptly tapering distally, the stems of the year, the lf-stalks (especially ventrally) and margins of the large plane leathery 2-3-jugate lfts livid-setulose, livid-verruculose, resin-dotted, or both setulose and viscid-puberulent, the faces of the lfts often glabrous but sometimes thinly pilosulous dorsally along and near midrib, or sometime? (both young and adult) finely pilosulous on both faces, the inflorescence a complex terminal exserted panicle of 1-several variably ramified racemes, the axes (and sepals) always viscid, commonly pilosulous and setulose, the pilosulous hairs sometimes lacking, the setules sometimes replaced by hispid setae. Stipules ascending or appressed, subulate or linear-subulate, 1-4(-5) mm, sometimes concealed by the dilated pulvinus, early dry and fragile, deciduous. Lvs horizontally divaricate or widely ascending (7-)9-18 cm, petioled; pulvinus ovoid, dilated but insensitive, 2-3.5 mm, coarsely wrinkled; petiole stout, 2.5-7 cm, at middle 1.1-2(-2.2) mm diam, proximally terete or subcompressed, upward obtusely 2-carinate and narrowly sulcate; rachis of 4-foliolate lvs (1-) 1,6-3.3(-3.7) cm, of 6-foliolate lvs up to 4-5.5 cm; lfts commonly 2, less often 2-3 or largely 3 pairs, of equal size or slightly accrescent distally, all displayed at right angles to the rachis, tilted edgewise to the meridian on horny, insensitive, when dry coarsely rugulose pulvinules (1 -) 1.5-3 mm, from ventral view appearing sessile, in outline orbicular to very broadly rhombic-or ovate-orbicular, obtuse, emarginate, or very broadly and shortly deltate-apiculate (2.5-)3-7.5(-8) cm in greatest diam, slightly longer to slightly shorter than wide, muticous or minutely mucronulate, at base sinuately truncate or shallowly semi-cordate, the (adult) blades stiffly coriaceous, not at all glutinous, dull olivaceous sometimes reddish- or purplish-tinged or bluish-green, on both faces commonly glabrous but sometimes dorsally or both sides thinly softly villosulous, the essentially entire but often irregularly crenulate margin greatly thickened, obtuse, in age corneous (in one local var. sharply thin-edged) either glutinously livid-setulose or livid-verruculose or resin-dotted, the subcentric midrib and (5-)7-10(-12) pairs of major secondary veins sharply raised both sides, the tertiary connecting and subsequent venules more slender but also elevated, forming an irregular mesh of areoles mostly up to 1.5-3.5 mm diam, a finer mesh sometimes prominulous and the reticulation then smaller. Inflorescence a complex narrow, corymbiform, or pyramidal panicle 1 -3(-4) dm composed of 1-several 1-3-times ramified (exceptionally simple) loosely few-fld racemes arising near together from nodes of a condensed, leafless or partly leafy-bracteate terminal axis, throughout densely viscid-villosulous and setulose, or the villi sometimes suppressed, or the setules exceptionally reduced to viscid warts, or (in a rare variety) replaced by hispid setae up to 1.5—3 mm, the individual racemes mostly 2-15(-20)-fld becoming 2-16(-20) cm; bracts subulate or lanceolate, entire or 3-denticulate, 1-3 mm, persistent; pedicels ascending 1.3-3.5 cm, bracteolate 0.5-9 mm below calyx; bracteoles like the bracts, 1-2 mm, persistent; buds ovoid or ovoid-ellipsoid, usually both villosulous and setulose, the villi sometimes 0, the setules rarely reduced to glandular verrucae, or (vars.) prolonged into hispid setae; sepals firm except for membranous margins, brownish-yellow, at anthesis widely expanded, elliptic to oblanceolate, obtuse, 8-16.5(-17) x (3.7-)4-6.6 mm; petals yellow sometimes with darker basal and central flash, very unequal, the four plane ones flabellate-cuneate, the adaxial largest, bannerlike, up to 17-35 x (16-) 17-35 mm, the fifth much shorter, falcately oblanceolate, coiled; ovary usually densely setulose, always glandular, the setules sometimes reduced to verrucae or mixed with pallid villi; ovules (5-)6-10(-11) Pod erect or ascending, linear-oblpng, (3-)3.7-6.5(-7.3) x 0.7-0.9(-1) cm, the valves glutinously castaneous, either setulose and villosulous, simply villosulous, or glandular-verruculose, in one var. hispid-setose; seeds (few seen) 6-6.5 x 4-4.5 mm, the testa dark brown, dull, lustrously lineolate- pitted.

Discussion

While C. orbiculata was first discovered in an outlying station in central Minas Gerais, its main range lies west of Rio Sao Francisco, where it extends the length of Espigao Mestre southward on both slopes from near 11° S and thence throughout the highlands of southern Goias as far as 50° W and 17° S. In this immense area the species is represented by a number of local but taxonomically insignificant races differing in stature, pubescence, leaflet-number, and flower-size. Crossing the boundary between Goia's and Minas in 1834, Riedel encountered C. orbiculata both in the form of a lowly bushlet and that of an arborescent shrub. His experience has been repeated often in modern times, and it seems impossible to distinguish between individuals that flower from diffuse or prostrate branches from those that become at maturity treelets with the crooked, trunk and irregularly rounded crown of typical cerrado life-form. The foliage of C. orbiculata was originally described as glabrous, and is commonly truly so except for the sticky setules or warts around the characteristically thickened rim of the leaflets, but close examination reveals, even in the type, a few hairs around and above the pulvinules, and plants with foliage fully glabrous and finely villosulous either beneath only or on both sides, but otherwise identical, have been found side by side (10 km s. of Brasilia. Irwin & Soderstrom 5633, Irwin & al. 8574; s. of Cristalina Irwin & at. 9731). The average flower of C. orbiculata has the enlarged adaxial petal about 2.5—3 cm long, but there are scattered records of extremely large flowers, up to 3.5 cm long, sometimes (as Irwin & al 18081), but not always, combined with 3-jugate leaflets. Over the greater part of the range of C. orbiculata all leaves are 4-folialate, but in south-central Goias and the Federal District a few 6-foliolate leaves occur sporadically among 4-foliolate ones, and locally in Chapada dos Veadeiros the 6-foliolate condition becomes dominant, sometimes linked with a decrease in size of the individual leaflets. But here again there seem to be no correlated differences in the habit or flower. The viscous inflorescence of C. orbiculata is ordinarily both villosulous and setulose, but the villi are sometimes lacking, and the setules may be pallid or yellowish, sparse or dense.

Isolated at the eastern and near the western edge of the species range are three forms sufficiently differentiated and geographically detached to deserve taxonomic rank. One. endemic to the thin mineralized soils of Serra Dourada in south-central Goias, already described as the distinct species C. trichothyrsus Harms, has the foliage and habit of typical C. orbiculata but an inflorescence and pod hispid with long yellow setae; we accept this as a variety. The two others are far distant in Serra do Espinhaço in Minas Gerais: a var ustulata, differing from the smaller, more diffuse and thinly villosulous states of var. orbiculata in having finely and intricately reticulate leaflets combined with flowers less than 2 cm long; and a var. cercidifolia which approaches C. celiae in the scarcely dilated, smooth margins of the leaflets, but differs from it in having one petal greatly reduced in size.