Senna multijuga (Rich.) H.S.Irwin & Barneby

Authors

Howard S. Irwin, Rupert C. Barneby

Authority

Irwin, Howard S. & Barneby, Rupert C. 1982. The American Cassiinae. A synoptical revision of Leguminosae tribe Cassieae subtrib Cassiinae in the New World. Mem. New York Bot. Gard. 35, part 2: 455-918.

Family

Caesalpiniaceae

Scientific Name

Senna multijuga (Rich.) H.S.Irwin & Barneby

Type

Typus infra sub. subsp, multijuga indicatur.

Synonyms

Cassia multijuga Rich.

Description

Species Description - Trees and treelets at maturity attaining 6-40 m with trunk 1-6 dm diam, often precociously flowering as shrubs only (3-)4-6 m, most commonly encountered as slender trees ±6-15 m, varying from fully glabrous to densely pilosulous throughout (as described for vars. following), the annotinous branchlets subterete verruculose canaliculate, the hornotinous ones ribbed, densely leafy, the long narrow multifoliolate lvs strongly bicolored, dark green (when dried often brunnescent) and dull or sublustrous above, pallid beneath, the inflorescence a fully exserted or at base partly leafy-bracteate, either simple thyrsiform or complexly branched pyramidal or pseudo-corymbose panicle of racemes, its axes commonly finely pilosulous, sometimes glabrous, sometimes setulose. Stipules 3-14 mm, either linear-setiform or asymmetrically dilated at base and the blade there undulate or replicate on itself, in any case caducous, absent from many mature flowering and all fruiting specimens. Lvs often ± heteromorphic, those low on annotinous branchlets and those in and near the panicle often shorter and simpler than the rest, the larger ones (6-)7-31(-35) cm (these only described hereafter); petiole including discolored, variably dilated pulvinus 4-32 mm, at middle 0.5-1.8 mm diam, shallowly margined and shallowly open-sulcate ventrally; gland between proximal pair stipitate or sessile, the stipe when present either glabrous or pilosulous, the whole in profile (0.8-)1-4.5(-5) mm, the ovoid or fusiform, sometimes lanceiform or hornlike body 0.3-0.65(-0.8) mm diam, a similar gland sometimes at second pair and (in var. multijuga) sometimes also at a few distal pairs, minute subuli- or verruculiform glands commonly present between all other pairs, these sometimes represented by a tuft of glandiform spicules or sometimes 0; pulvinules (as seen in dorsal view) 0.3-2(-2.4) mm; lfts (13-)15-56 pairs, inserted along rachis at points 1.5-13(-16) mm apart, very gradually decrescent upward and downward from a point below middle of rachis, the whole blade in expanded outline therefore very narrowly lanceolate, the larger lfts varying from linear or linear-oblong to lance- oblong, oblong or oblong-elliptic, deltately subacute, obtuse or truncate-emarginate, the largest 0.75-5.3 cm, usually conspicuously mucronulate by the excurrent costa, at base strongly inequilateral, the margins usually revolute at least near the pulvinule, sometimes plane, the midrib cariniform beneath, immersed or impressed above, the secondary venation of 5-11 major camptodrome (sometimes with intercalary) pairs either fully immersed or prominulous, but only delicately so, on one or both faces, tertiary venulation 0 or faint and irregular, sometimes immersed but discolored beneath. Peduncles 1-4.5(-6) cm; racemes 3-16(-25), the more vigorous of any panicle mostly at least 5-fld, the axis becoming (0.2-)0.4-4(-8) cm, but some distal racemes of a complex panicle often depauperate and 2-5-fld with axis 0.1-0.4 cm; bracts lance-elliptic or ovate cymbiform (1-) 1.5-6 mm, shielding the very young bud but early caducous; pedicels becoming (13-) 14-32 mm, not subtended by a gland; buds globose when very young, opening long before true anthesis, glabrous or basally puberulent; sepals when mature subpetaloid, yellow, greenish or brownish, strongly graduated, obovate or orbicular very obtuse, the smaller firmer outer ones ±1/2-1/3 as long as the inner, the longest (3.5-)4-7.5(-8) mm; petals yellow, commonly glabrous dorsally, sometimes puberulent externally along veins, heteromorphic, the 3 adaxial and 1 abaxial similar (except the latter often larger), obovate-oblanceolate 7-21 mm, contracted into a stalklike claw, the fifth (abaxial, alternately right and left up the raceme) sessile, very obliquely semi- ovate or boomerang-shaped, coarsely veined, commonly largest of all and (measured along the mid-vein) 14-23(-25) mm; androecium usually glabrous, the free filaments rarely and anthers exceptionally pilosulous, the filaments of 4 median and 1 latero-abaxial stamens 0.6-2.3 mm, those of 2 abaxial ones (1.8-)2.5-7(-9) mm, the anthers of 4 median stamens slightly incurved, at apex truncate or obscurely strangulated into a short neck, the lateral beak 0.3-0.5 mm, dehiscent by 2 parallel slits, the body of 3 abaxial stamens lunately incurved (4.5-)5-9 mm, contracted into a porrect, ventrally 2-porose beak (0.8-)1-1.8(-2.2) mm; ovary glabrous, glabrous laterally but ciliolate, pilosulous overall, or both pilosulous and remotely pilose; style 1-2 x 0.3-0.6 mm, glabrous; ovules 48-76. Pod erratically geotropic in attitude, stipitate, the stipe 2-9 mm cuneately dilated upward, the broadly linear, abruptly obtuse body (6.5-)8-20 x 1. 3-2.1 (-2.5) cm, bordered by prominulous sutures undulately constricted only at aborted ovules, the very flat reddish or purple-castaneous, seldom greenish, ultimately papery, nigrescent, transversely venulose valves obscurely expressed over seeds as narrow transverse mounds, the interseminal septa 2-4 mm apart, the individual seed-chamber much wider than long; seeds narrowly oblong or oblong-ellipsoid, bifacially or subquadrately compressed (4.3-)4.8-8(-9) x 1.5-2.1 mm, the pale brown or fawn-gray testa dull or sublustrous crackled, the linear or linear-elliptic areole 2.3-4.5 x 0.25-0.5 mm, 5-11 times as long as wide.

Variety Key - Key to Subspecies and Varieties of S. multijuga 1. Stipules at base inequilaterally dilated, the herbaceous blade there 0.8-2.5 mm wide and undulately crimped or folded on itself; Amazon Basin from s. Goias, Brazil and Yungas, Bolivia n. to s.-e. Colombia, Guayana Highland, the Guianas, Trinidad, and the s. affluents of the Orinoco in Venezuela; disjunct in coastal s.-e. Brazil (Bahia); cultivated or naturalized or both in Colombia (Meta), Panama, Costa Rica, West Indies, East Indies, and widely planted in tropical botanical gardens: subsp, multijuga: 2. Lfts of larger lvs 16-31 pairs, up to ±2-5 cm long, inserted at points up to (5-)6-11 (-15) mm apart along rachis; range as given except coastal s.-e. Brazil. 161/Ia. var. multijuga (p. 495). 2. Lfts of larger lvs 26-56 pairs, up to 0.8-1.4 cm long and inserted at points 1.5-4 mm apart along rachis; s.-e. Brazil (Bahia, Espirito Santo). 161/lb. var. verrucosa (p. 496). 1. Stipules linear-attenuate or setiform, equilateral at base and there not over 0.6 mm wide, both margins plane; native either in s.-e. Brazil (coastal centr. Bahia to centr. Minas Gerais, s. to Santa Catarina) or s.-e. Mexico (Veracruz, Oaxaca, Chiapas); naturalized in s.-e. Venezuela (Bolivar) and n.-w. Colombia (Bolivar); subspp. lindleyana and doylei:3. Lfts at once relatively long or relatively broad (or both), the larger ones at least 2 cm long and 5.5 mm wide, and spaced at points up to (5-)6-11(-15) mm apart along rachis; native in s.-e. Brazil, cultivated in United States, Fiji and probably elsewhere. 161/IIa. var. lindleyana (p. 498). 3. Lfts smaller and narrower, the largest not over 15 mm long or over 4.5 mm wide and spaced up to 2.5-5 mm apart along rachis; one sympatric, one remotely allopatric. 4. Pairs of lfts in larger lvs 15-32; coast ranges of s.-e. Brazil (Rio de Janeiro to Santa Catarina), sympatric with var. lindleyana, naturalized in Venezuela and Colombia. 161/IIb. var. peregrinatrix (p. 499). 4. Pairs of lfts in larger lvs 33-53; s.-e. Mexico (Veracruz, Oaxaca, Chiapas). 161/III. subsp, doylei (p. 500).

Discussion

Our concept of S. multijuga is the traditional one established in Bentham’s monograph, modified only so as to accommodate Cassia verrucosa (as predicted necessary by Bentham himself) and the more recently described C. doylei. So defined it differs from other Interglandulosae, except S. mutisiana, S. williamsii and some plurifoliolate forms of S. pallida and S. acuruensis, in the numerous leaflets (at least 16 pairs in larger leaves), from the first two just mentioned in the smaller sepals (the large inner ones ±4-7.5, not 8-14 mm) and lack of lustrous hispid setae on the young stems, from all of S. pallida in the several-flowered racemes and absence of fusiform glands at base of the pedicels, and further from all these three together in the very broad pod and narrowly oblong seeds. Its closest relative, S. acuruensis, which is vicariant in the seasonally arid caatinga country of northeastern Brazil, resembles S. multijuga in the pod and seeds, but in those cases where the leaflets (in var. acuruensis only) attain equality in number the leaf-stalks and axes of inflorescence are densely viscid-setulose. The species varies much in stature, sometimes flowering as a softly woody arborescent shrub but capable of attaining the port and girth of a genuine forest tree. The vesture varies erratically in density, in quality, and independently in color from whitish to sordid or golden-yellow, the filiform hairs being mixed in some populations both north and south of the Amazonian Hylaea with erect orange setules. Bentham already commented on the range of flower-size, which now appears to be both seasonal and racial, although the determining factor is often open to conjecture. Most arresting visually is the variation in size and number of leaflets, the two modes of variation being mutually adjusted to stabilize the total photosynthetic area exposed to sunlight and simultaneously governing the distance between pairs of leaflets along the rachis, smaller leaflets being always more crowded. Finally the stipules, though inconveniently caducous and lacking from most mature specimens, vary with significant geographic correlation from linear-setiform to basally dilated and falcately hemilanceolate in outline, the dilated blade being nearly always undulate or folded on itself. Analysis of the phenetic variation has shown that S. multijuga can be divided into three major geographic blocs by the character of the stipules, blocs that coincide with recognized patterns of floristic dispersal. The dilated stipule is circum-Hylaean and Guayanan, with a detached outpost in the wet coastal forest of Bahia. The setiform stipule replaces this in southeastern Brazil southward from central Bahia and is the only type encountered in Mexico. Within each of the two South American blocs, which we term subspecies, are encountered parallel modifications of size and number of leaflets, taxonomically recognized at the varietal level. A random variation in vesture is found almost throughout South America but is feebly, if at all, correlated with dispersal or with other phenetic characters. Senna multijuga is one of the handsomest of the Neotropical sennas, an ornamental tree of rapid growth, free of disease and prolific in flower. Its var. multijuga was early taken into cultivation and by mid-XIX century was already naturalized in Malesia and southern India, probably having been brought originally by the Dutch from Surinam to Java. Other introductions, from Trinidad to Puerto Rico, of a setulose form of var. multijuga into Martinique, of var. lindleyana into Fiji, very likely from Rio de Janeiro, and into California from Sao Paulo, are a matter of record, but the origin of much of the material planted in the American tropics as a garden or street tree is lost to view. The literature contains records of Cassia multijuga, sens, lat., from Argentina (Tucuman), Central America, and West Indies, but we have found no evidence that it is native in any of these countries. Key to Subspecies and Varieties of S. multijuga 1. Stipules at base inequilaterally dilated, the herbaceous blade there 0.8-2.5 mm wide and undulately crimped or folded on itself; Amazon Basin from s. Goias, Brazil and Yungas, Bolivia n. to s.-e. Colombia, Guayana Highland, the Guianas, Trinidad, and the s. affluents of the Orinoco in Venezuela; disjunct in coastal s.-e. Brazil (Bahia); cultivated or naturalized or both in Colombia (Meta), Panama, Costa Rica, West Indies, East Indies, and widely planted in tropical botanical gardens: subsp, multijuga: 2. Lfts of larger lvs 16-31 pairs, up to ±2-5 cm long, inserted at points up to (5-)6-11 (-15) mm apart along rachis; range as given except coastal s.-e. Brazil. 161/Ia. var. multijuga (p. 495). 2. Lfts of larger lvs 26-56 pairs, up to 0.8-1.4 cm long and inserted at points 1.5-4 mm apart along rachis; s.-e. Brazil (Bahia, Espirito Santo). 161/lb. var. verrucosa (p. 496). 1. Stipules linear-attenuate or setiform, equilateral at base and there not over 0.6 mm wide, both margins plane; native either in s.-e. Brazil (coastal centr. Bahia to centr. Minas Gerais, s. to Santa Catarina) or s.-e. Mexico (Veracruz, Oaxaca, Chiapas); naturalized in s.-e. Venezuela (Bolivar) and n.-w. Colombia (Bolivar); subspp. lindleyana and doylei:3. Lfts at once relatively long or relatively broad (or both), the larger ones at least 2 cm long and 5.5 mm wide, and spaced at points up to (5-)6-11(-15) mm apart along rachis; native in s.-e. Brazil, cultivated in United States, Fiji and probably elsewhere. 161/IIa. var. lindleyana (p. 498). 3. Lfts smaller and narrower, the largest not over 15 mm long or over 4.5 mm wide and spaced up to 2.5-5 mm apart along rachis; one sympatric, one remotely allopatric. 4. Pairs of lfts in larger lvs 15-32; coast ranges of s.-e. Brazil (Rio de Janeiro to Santa Catarina), sympatric with var. lindleyana, naturalized in Venezuela and Colombia. 161/IIb. var. peregrinatrix (p. 499). 4. Pairs of lfts in larger lvs 33-53; s.-e. Mexico (Veracruz, Oaxaca, Chiapas). 161/III. subsp, doylei (p. 500).