Cassia absus

  • Title

    Cassia absus

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Cassia absus L.

  • Description

    164.  Cassia absus Linnaeus, Sp. PI. 537. 1753. — Holotypus sub var. absus indicatur infra.

    Monocarpic but potentially of extended duration and in age lignescent at base, highly plastic as to stature and amplitude of foliage, in arid circumstances flowering as a simple or almost simple erect monopodial herb 1 dm upward, in richer or moister soils developing from near as well as above the base of the central erect axis (itself seldom over 6 dm) several or many incurved-ascending branches up to 1(-1.5, reportedly -2) m, these sympodially branched, each terminal raceme being surpassed by the accompanying axillary branchlet, the usually ample foliage becoming distichous distally, the ultimate axillary branchlets slender or subfiliform and terminating in a depauperate raceme, the stems, lf-stalks and axis of inflorescence usually at once finely villosulous and hispid or hispidulous with yellowish setae to (0.4-)0.6-1.8(-2) mm, the membranous, faintly bicolored fits either villosulous on both sides and also setulose on margins and on veins beneath, or glabrous above, or glabrous on both sides and ciliolate, rarely quite glabrous, the inflorescences mostly immersed in foliage, some rarely exserted.

    Stipules thinly herbaceous or submembranous with firm midrib, at first or permanently ascending to spreading-recurved, sometimes in age reflexed, becoming stramineous or brownish, narrowly triangular-acuminate to narrowly lanceolate, (0.8-) 1.2-5 mm, persistent.

    Lvs widely ascending, divaricate, or somewhat deflexed, (1.5)2-9(11.5) cm, petioled, the petiole usually 1-2 times as long as the proximal leaflets, rarely a trifle shorter; pulvinus at base slightly transversely dilated, commonly discolored, shrunken when dry, 0.7-1.8(-2) mm; petiole (0.7-)1-5 cm, at middle openly shallow-grooved and (0.25-)0.3-0.7 mm diam; rachis (1.5-)2-11 (-14) mm; lfts 2 pairs, the distal pair larger, tilted forward from rachis, 14 face-to-face, on densely hispidulous, ventrally grooved pulvinules 0.4—1.6(-2) mm, in outline obliquely broad- obovate obtuse to rhombic-elliptic or -ovate and deltately subacute, minutely mucronulate, (5-)8-46 x (3-)5-28 mm, at base broadly rounded to subcordate on proximal side and cuneate to narrowly rounded on distal side, the entire, villosulous or setulose, rarely glabrous margin plane or incipiently revolute, the blades pale-olivaceous and dull both sides, slightly paler beneath, the slender midrib and (3-)4-6 pairs of secondary veins beneath pallid, sharply and finely prominulous, above either faintly raised or immersed, the tertiary venulation imperceptible.

    Racemes erect, sessile (the first, sometimes also the second flower leafy-bracteate), mostly 8-20-, exceptionally up to 40-fld or in some delicate and dwarf forms only 3—7-fld, the axis rapidly elongating below the 1-several simultaneously expanded fls but little prolonged above them, the nodding buds subcorymbose, the stiff stout or (few-fld) slenderly flexuous axis becoming (1-)1.5-13, exceptionally 25-30 cm; bracts submembranous, green, spreading or in age reflexed, ovate to cordate, semiamplexicaul, abruptly acute or acuminate, entire or often denticulate, 1-2.5 mm, persistent, within at base fimbriate-appendaged; pedicels at anthesis widely spreading-ascending, very slender, 1.5-4 mm, after fertilization quickly thickened, in fruit ascending, usually shallowly sigmoid, 3-6(-7.5) mm, bracteolate 0.5-4 mm below calyx; bracteoles about half as long and wide as bracts, 0.3-1.3 mm, persistent or tardily deciduous; buds ovoid or oblong-ellipsoid, obtuse, commonly setulose, sometimes also finely villosulous, rarely glabrate; sepals submembranous, pale green or red-tinged, narrowly lanceolate, narrowly oblong-elliptic, or (inner) ovate, obtuse or subacute, 3-4.7 x 0.8-2.1 mm; petals all erect, forming a campanulate perianth, yellow, early fading orange-brown or brick-red, nearly homomorphic and either of equal length or the 3 adaxial slightly longer, four symmetrically spatulate, the longest 4.3-7.2 x (0.8-) 1-3.2(-3.7) mm, the obtuse or subtruncate blade narrowed into a slender claw about half as long, the fifth petal similar but obliquely dilated on one side of midnerve; stamens 2-7, commonly 4, 5, or 6, the 1-3 adaxial usually longest, the 2 abaxial out of 7 and often 1 out of 5 smaller than the rest, sometimes dwindling to a staminode, the filaments 0.91.8 mm, the anthers 1.1-2.8 x 0.45-0.75 mm, the sutures minutely barbellate, the connective muticous or produced into a minute papilla; ovary usually villosulous along sutures and densely setose on faces, rarely glabrescent or quite glabrous; style 1.4-1.9 mm, grooved ventrally, dilated and incurved upward; ovules (4)5-8(10).

    Pod linear-oblong, straight or slightly curved forward, (22-)24-50 x (5-)5.5-7(-8) mm, the pale green valves turning stramineous or brown, nearly always hispid-setose, commonly also minutely sparsely pilosulous, but the villi often and the setae rarely also absent.

    Seeds compressed, broadly obovoid, pyriform or bluntly trapezoid, 3.4-4.8(-5.1) x 2.4- 3.6(-4.1) mm, the testa glossy black or mahogany-black, strongly or faintly pitted in lines.

    While C. absus greatly resembles in habit and appearance the perennial 4-foliolate cassias with which Bentham (1871) associated it in his series Absoideae of sect. Absus, it differs from all that have hitherto been supposed close kindred in two points: the presence of an interpetiolular appendage, often misinterpreted as a gland, between each pair of leaflets, and the modified structure of the flower. It is further distinguished by the syndrome of a monocarpic (but sometimes prolonged) life-span coinciding with distichous phyllotaxy of the mature branches. These two last features, commonly encountered together in sect. Chamaecrista, occur exceptionally, but never together, in what we now term sect. Absus, monocarpy in C. (subsect. Otophyllum) debilis, and distichous leaves in C. (subsect. Baseophyllum) coriacea and C. (subsect. Absus) belemii. Several Chamaecristae have small, autogamous flowers and reduced androecium technically similar to those of C. absus, but retain the characteristic axillary few- flowered racemes, eglandular vesture, and plurijugate leaflets of their group.

    The interpetiolular appendages of C. absus take the form of a little tonguelike blade arising from the leafstalk, that between the lower pair commonly broad-lanceolate or triangular, that between the distal pair narrower, both commonly denticulate or fimbriolate, and either green or less often livid in color. They appear quite different in shape, origin, and function from the urceolate or saucer-shaped petiolar glands found in sects. Apoucouita, Chamaecrista, Xerocalyx, or subsects. Baseophyllum and Otophyllum of sect. Absus. The appendages of C. absus may become sticky with the viscous effluvium secreted by the setules of the leafstalk near at hand, but are apparently not themselves secretory organs. There has been much disagreement in the literature over terminology for the intrapetiolular appendage. Bentham (1871, p. 558) in his definition of ser. Absoideae makes an exception of C. absus as the one member with a petiolar gland. Latterly Aubreville says (1970, p. 59) "petiole et rachis sans glande." De Wit finds a "ligulate-acute glandlet", whereas Steyaert sees the same as "appendice aciculaire (glandulaire?) caduc" but only at the lower pair of leaflets. It is faithfully figured by Brenan (1967, p. 82, fig. 2, 3) and there called a gland, but in the accompanying description its nature is properly called into question. In many species of sect. Absus (see in particular C. mollifolia) there occur between pairs of leaflets, and sometimes also axillary to stipules and floral bracts, one or several clustered spicules, either greenish or nigrescent, which seem from their position homologous to the intrapetiolular scale of C. absus. In this connection it is interesting that the bracts and stipules of C. absus give rise adaxially, at their junction with stem or inflorescence axis, to fimbriolate scales which appear quite similar, except more deeply divided, to the narrow appendage between the distal pair of leaflets. The true nature of these structures, possible stipellar in origin, and their function, if any, remain unexplained.

    The substantial basis for segregation of C. absus as a monotypic section within subgen. Lasiorhegma is the little autogamous flower, notable for the small size and short duration of the corolla, the reduced androecium of 2-7 (rarely 8) members, and the short scoop-shaped style. At the last stage of praefloration, when the petals are beginning to emerge from the calyx but are still tightly coiled together, the pores of the anthers are already dehiscing and discharging pollen, and the stigma is already receptive. The adaxial stamen, one of the two or three largest in the complement of 2-7, lies in bud directly opposed to the style, so oriented as to emit a stream of pollen either directly onto the stigma or, if a little shorter than style, directly into the style's ventral groove. Carefully dissected buds of this age often reveal pollen grains adherent to the minutely fringed stigma, and a plant of C. absus, grown isolated in the greenhouse at NY in summer of 1973, produced many pods and quantities of viable seed. At full anthesis the perianth opens briefly into a narrow cup, directed obliquely downard; the petals quickly fade orange-brown to deep red and by early afternoon of the same day are mostly withered and falling. The one lateral abaxial petal of the C. absus flower that corresponds to the hetermorphic petal of sect. Chamaecrista retains evidence of its origin in being a little transversely dilated on one side, the dilated side alternating from flower to flower upward along the raceme, in the enantiomorphic tradition of sect. Chamaecrista or Apoucouita. But here the organization of the flower has been modified to promote or even ensure self-fertilization and the heteromorphic petal has accordingly lost its functions of a landing-platform for visiting bees (Chamaecrista) or a baffle interposed between style and stamens. It seems likely that the small, irregularly pentandrous flowers of such Chamaecristae as C. nictitans have developed in parallel ways.

    Starting with Colladon (1816, p. 116) the androecium of C. absus has generally been described as pentandrous, but Britton & Brown (1930, p. 299) allow sometimes seven, and Steyaert (1952, p. 508) four to six members. It should be remembered, however, that Roxburgh had as early as 1814 described from Bengal a tetrandrous C. exigua which has been lost to sight since its reduction without comment by Bentham (1871) to C. absus. A systematic check of all our material shows that the number of stamens, while indeed most often five, in reality varies from two to eight, the extremes of two and eight being, however so rare that in practice one may evaluate the normal range at three to seven. When exactly five stamens are present, one or two of the abaxial ones are commonly smaller than the rest; when there are over five, two or more are smaller. As the number dwindles, it is the adaxial stamen and one or two immediate oppositisepalous neighbors that survive.

    A study of the distribution of stamen numbers has theoretical interest for its possible bearing on the geographical origin of C. absus, a species traditionally thought to be palaeotropical, even though its near kindred are all endemic to the Americas. Analysis of large collections show that stamen number is very constant within-populations, as are other small phenetic characters of vigor, branching-pattern, length of raceme, and density of setulose and villosulous vesture. All of these seem to be inherited, as one might expect in a species that has adopted systematic inbreeding. In the material at our disposal — we have not seen the type of C. exigua — we found no example of less than five stamens in Africa, India and Ceylon, Malesia, or Australia; nor any in South America, Netherlands Antilles, Grenadines, or Jamaica. It is otherwise in North America, but the pattern is complex. In highland Costa Rica, Honduras, and Guatemala 5-6-merous androecia are commonest, but we have one 4-merous from Honduras and three from Guatemala- In Mexico pentandrous C. absus occurs in lowland Veracruz, very locally in the Balsas basin in Mexico State (mun. Temascaltepec), and has been encountered once only, greatly isolated, in the suburbs of Culiacan in Sinaloa, where it may well have been recently introduced. From central Jalisco northward to s.-e. Arizona (disregarding the exception from Culiacan just mentioned) and in the Cape mountains of southern Baja California, the androecium is never more than 4-, oftenest 3-, rarely 2-merous. From field labels it seems likely that the majority of these tetramerous forms occur in relatively undisturbed conditions, often remote, as on Sierra Surutato in Sinaloa, or the Baboquivari Mountains in Arizona, from centers of population and commerce. There is strong presumptive evidence that this reduced type of C. absus, which we describe below as var. meonandra, is indigenous in western Mexico.

    Evidence favoring the native status of pentamerous C. absus in Africa and India or both is equally strong. Assuming that the Absus of Prosper Alpinus is correctly identified with our plant, C. absus was in Egypt, though very likely only cultivated, before 1640. The natural range of weedy plants is always difficult to ascertain, and the problem becomes more acute in the case of species such as C. absus, used from antiquity in popular medicine for treatment of ophthalmia and a variety of lesions of the skin. It occurred in Ceylon early in the XVIII century (Burman, Hermann) and both Robert Browne and Banks & Solander encountered it in stations on the coasts of northern Australia at a time when these were virtually virgin territory. Today it is well known to be often of weedy occurrence in Africa (Brenan, 1967, p. 81); in Ethiopia Serrato Valenti (1971 p. 73-4) reports it adaptable to a great range of ecological conditions between the coastal plain and the mountainous interior up to 1700 m. De Wit (1955, p. 279) brands it an introduction in Malesia, though locally abundant in Java, Timor, and Celebes. Detached occurrences of C. absus in northern Pakistan (Ali, I.c.), southern Iran, (Hooper in Kew Bull. 1931, p. 308) and Arabia are probably artificial and secondary.

    The earliest record of C. absus from the New World seems to be that of De Candolle (1825, p. 500), who had received specimens from Jamaica, presumed introduced. In 1871 Bentham recognized the species only from tropical Africa, Asia, and Australia; but it had been collected a little earlier (1865) in Venezuela by Moritz, as well as in Jamaica. The first records from Brazil, Paraguay, Bolivia, Peru and Ecuador date back no further than the end of the XIX and early XX centuries and the extremely scattered and discontinuous occurrence as known at the present time is incompatible with an aboriginally native status. In Mexico the record starts with Palmer and Pringle in Jalisco, in 1886 and 1889 respectively, and T. Brandegee in Baja California in 1899, these uniformly 2-4-merous. The pentamerous form appeared first in Costa Rica in 1899 (Tonduz), quickly followed by records from Veracruz in 1906 and that already mentioned from Culiacan in 1904 (Brandegee). The range of pentamerous C. absus remains in Mexico, as in South America, discontinuous and random, of a sort unlikely for a native element of the flora, and in this respect quite different from that of tetramerous var. meonandra which, if reservations about the Guatemalan outposts are allowed, follows an established floristic pattern. There seems some support in these data for the hypothesis that 5-7-merous introduced and native 2-4-merous forms of C. absus coexist in Mexico and Central America.

    In Brazil C. absus, always 5-merous, is known from only five collections, none over forty-five years old. The single one from the Amazon delta in Para (Macapa) is of a common villosulous type, readily matched in fine detail with African and some few Mexican phenotypes. The other four, from coastal Ceara, Paraiba, and Pernambuco, differ collectively in being glabrous except for hispid setules, the leaflets being quite hairless on both faces, and we have found no Old World C. absus exactly similar. It is an odd circumstance that an introduced phenotype, apparently confined to a homogeneous habitat in northeastern Brazil, should be one that is not known to occur in the supposed fatherland of its species, one that is not covered by any detailed description of C. absus based on purely Old World material 1). Once again there arises a question as to whether a native strain of the species may not exist in northeastern Brazil, close to the principal focus of speciation in subgen. Lasiorhegma and in particular of that group of Absoideae which it most closely resembles in habit.

    Two hypotheses, starting from the assumption that all Neotropical C. absus has reached the Americas in post-Columbian time, are theoretically defensible. In the first, the strains now present would have arisen by means of several independent introductions carrying minutely distinctive genetic potential, and here maintained in pure form by autogamy. lf this were true, forms exactly similar to each and every introduced one should be discoverable in Africa or India. The second hypothesis requires only a single but accomodates several separate introductions; some of these however are subject to rapid selective evolution subsequent to establishment in America. By the first criterion var. meonandra and the unnamed form from northeastern Brazil descend from variants as yet unrecognized in their home country; by the second they are endemic modern derivatives. The evidence at hand is insufficient for solution of the problem, which might however yet yield to a detailed biosystematic study. For the present we think it taxonomically useful, however, to distinguish at level of variety the form with reduced androecium and more or less continuous range along the Pacific slope of Mexico. Whether this is the equivalent of Cassia exigua Roxburgh remains to be determined.

    Key to the varieties of C. absus

    1. Androecium commonly 5-merous, but often with 1 -2(-3) smaller but fertile intercalated members; Africa, s. Asia, Malesia, n. Australia, probably introduced and naturalized in the Neotropics, but very rare on the Pacific slope of Mexico.

    164a. var .absus

    1. Androecium (2)3-4-merous; w. Mexico, from Jalisco n. just into s. Arizona, and disjunctly

    in Guatemala and Costa Rica; possibly also (or originally) in s. India.

    164b. var. meonandra