Cassia cathartica

Title

Cassia cathartica

Author(s)

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Cassia cathartica Mart.

Description

5.  Cassia cathartica Martius in Spix & Martius, Reise Brasil. 1: 548. 1823.

Erect or assurgent, intensely glutinous subshrubs from knotty xylopodia becoming shrubs with blackish, leafless but scarred trunks corymbosely or paniculately branching distally into a derise crown of foliage, at anthesis (0.3-)0.5-2.5 m, except for the simply villosulous (rarely glabrate) upper If-face densely viscid-villosulous and hispidulous throughout with weak yellowish or livid setules to 0.25-0.8 mm, the foliage bicolored, the lfts either brownish-nigrescent or bluish-green above, paler brown-olivaceous beneath, the not or scarcely exserted racemes leafy- bracteate throughout, the fls therefore appearing solitary and axillary.

Stipules erect or spreading, narrowly subulate or setiform, (0.6-) 1-4(-5) mm, either tardily or promptly deciduous.

Lvs ascending or spreading on arcuately recurving If-stalks, either homomorphic or heteromorphic (as described under the vars.), 2-16 cm, shortly petiolate; pulvinus little dilated, sometimes livid, 1-2.4 mm; petiole (4-)6-22(-25) mm, at middle subterete but narrowly sulcate, 0.5-0.85 mm diam; lfts of major lvs (2-)3-18 prs, ascending from rachis, turned half face to face on discolored, scarcely dilated pulvinule 0.6-1.3 mm, either accrescent or decrescent distally, in outline oblong- to lance-elliptic, ovate, or oblong-ovate, mostly obtuse minutely mucronulate, sometimes subacute or shallowly emarginate, 7-30 x 3-13(-16) mm, at base ¹/2-cordate to rounded on proximal side, subcordate to broadly cuneate on ventral side, the entire margin revolute or almost plane, the blades submembranous or chartaceous, above varying from dark green and nigrescent to bluish-green or brownish-olivaceous, finely villosulous or glabrate, beneath paler, both villosulous and setulose, the midrib and 3-6(-7) pairs of major secondary veins above immersed or faintly prominulous, elevated but very slender beneath, the tertiary venulation obscure or imperceptible.

Fls solitary in axils of 3-many distal lvs, 1-2 of each branchlet simultaneously expanded and elevated ±to or beyond the buds; pedicels strictly ascending, (1.5-)2.2-4.3 cm, bracteolate 1-7 mm below calyx; bracteoles resembling stipules, 1.5-4 mm, deciduous; buds shortly before anthesis becoming horizontal or nodding, ovoid-acuminate or -apiculate, simply setulose or villous-setulose; sepals red or red-tinged, ovate-to obovate-elliptic, acute, the longer ones (8-)9.5-15 x 3-6.5 mm; petals bright yellow, 4 subrotately expanded, strongly unequal, the adaxial 1 largest, broadly obovate-flabellate, (14-) 16-24 mm long and ±aswide, 1 abaxial slightly smaller, 2 intervening usually much shorter and proportionately narrow, obovate to oblanceolate, the fifth yet shorter, erect, obliquely obovate or dimidiate, coiled; ovary densely viscid-setulose; ovules 3-9.

Pod oblong, oblong-elliptic, or linear in outline, straight or curved downward, (17-)20-36 x 6.5-10 mm, the livid-castaneous, ultimately blackish valves glutinously setulose; seeds 3.8-5.4 x 1.7-2.5 mm, the usually lustrous, rarely dull black testa faintly lineolate.

The Sene do Campo of the Brazilian Planalto, long used as a native substitute for the cathartic senna of the Old World tropics, is an intensely glutinous cassia widespread over highlands of southeastern Brazil, where it may be instantly distinguished from all but the rare C. adenophora by the presence of a pinnate leaf under each flowering pedicel, the flowers therefore solitary and axillary, not racemose. The technically similar C. adenophora, highly localized in Distrito Federal, where C. cathartica is unknown, differs from var. cathartica, the only form of the species occurring in neighboring Goias or Minas Gerais, in the syndrome of simple stems, plane leaflets, and smaller, less irregular flowers, of which the dimidiate petal is longest and not by much the shortest of the five.

As here defined, C. cathartica is a polymorphic assemblage of minor forms variable both between neighboring populations and to some degree within them. Flowering plants vary much in stature, taking the form sometimes of a humble undershrub 3-5 dm tall with one or few equably leafy stems rising directly from a xylopodium, and sometimes that of a shrub up to 2 m tall with naked black trunks paniculately branched distally into a wide rounded head of foliage. It is not known to what degree size of the plant at anthesis is genetically determined, or whether stature is simply a reflection of age or accidents of environment. The foliage of C. cathartica is often heteromorphic, the primary cauline leaves produced before anthesis being often longer and more complex than those associated with the flowers. And the flowers themselves are quite variable in size, particularly in the amplitude of the large, adaxial and abaxial petals. At relatively great elevations in the southern Serra do Espinhapo the species is represented by a series of forms in which all leaves, and not merely the uppermost, are reduced in length and number of leaflets. We suspect that members of this series may be independently derived from more typical, plurifoliolate, vicariant or sympatric races of the species, but it seems convenient for the present to unite them under a comprehensive var. paucijuga, of which the internal variation is analyzed below.