Senna birostris (Dombey ex Vogel) H.S.Irwin & Barneby
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Authors
Howard S. Irwin, Rupert C. Barneby
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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 1: 1-454.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Typus infra sub var. birostri indicatur.
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Synonyms
Cassia birostris Dombey ex Vogel
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Description
Species Description - Bushy shrubs at anthesis 0.4-3(-4) m, exceptionally arborescent to 6 m, with castaneous or atropurpureous annotinous branchlets, variable in pubescence (as described for each var.) from subglabrous to densely pilosulous, the subconcolorous or bicolored foliage dull olivaceous, the lfts veinless above, costate and sometimes also finely penninerved beneath, the racemes mostly axillary to and shorter than a fully developed lf, either all lateral to branchlets or crowded into a terminal panicle. Stipules submembranous or thinly herbaceous, if greenish then soon dry and brownish, mostly linear-lanceolate or -attenuate and 2.5-11 x 0.2-1.2 mm, less commonly broader and firmer, up to 1-1.5 mm wide, then suboblique at base and incipiently replicate marginally, in any case deciduous before the lf. Lvs mostly (4-)5-15(-21) cm (some low on lateral branchlets, or in the panicle, shorter and simpler, but not further noticed); petiole including little swollen pulvinus 6-27(-35) mm, at middle (0.4-)0.5-1.2(-1.6) mm diam, obtusely 3-ribbed dorsolaterally, shallowly open-sulcate ventrally; rachis (2.5-)3-10.5 cm; petiolar gland (much eaten) between or above proximal, sometimes displaced to between second pair of lfts, stipitate, in profile (1-)1.3-3(-3.4) mm tall, the slenderly ellipsoid acute or thicker claviform subobtuse head (0.1-)0.2-0.8 mm diam, rarely a second gland between the second (third) pair; pulvinules 0.3-2.2 mm; lfts (5-)6-14(-16) pairs, slightly decrescent toward base or toward both ends but otherwise of subequal length, in outline varying from narrowly lanceolate, lance- oblong or elliptic either acute mucronulate or obtuse acuminulate to ovate or ovate-oblong acute obtuse or subemarginate, the longest (6-)7-30(-32) x (2-)3-12 mm, (1.5-) 1.7-5 times as long as wide, at base inequilaterally cuneate or obliquely rounded, the margins plane, the centric midrib depressed or immersed above, cariniform beneath, all subsequent venation fully immersed on both faces or 4-7(-9) pairs of faint discolored but not or scarcely prominulous, often imperfectly camptodrome secondary venules visible beneath. Racemes loosely (4-)7-35(-40)-fld, the axis and peduncle together becoming (2-)2.5-14 cm, the open fls usually raised ± to level of the nodding buds, but these sometimes (var. birostris only) racemosely disposed above them; bracts submembranous, lance- or elliptic-attenuate (2-)2.5-8 x 0.6-1.4(-2) mm, deciduous by or long before anthesis; pedicels (12-)14-26(-29) mm; fl-buds subglobose, glabrous or pilosulous; sepals submembranous pallid or yellowish and toward middle commonly fuscous or purplish, obovate-suborbicular or oblong-obovate, not much or strongly graduated, the 2 outer ones 2.5-7 mm, the longest inner one 4.3-10.5 mm; petals yellow (whitening or not when dried, dark-venulose) glabrous, subhomomorphic or the vexillary one broader than the rest and emarginate, the lateral and abaxial pairs obovate or oblong-obovate beyond short claw, up to (6-)7-14 x 3-10 mm; androecium glabrous, the filaments of 4 median stamens 1.5-2.5(-2.8) mm, of 2 latero-abaxial ones 2.2-11 mm, of the centric abaxial one (1.8-)2-7 mm, the anthers of the 4 median stamens 2.4-4.8 mm, of the 3 abaxial ones usually subequal (3.5-)4-7.5(-7.8) mm, but the centric abaxial stamen rarely (var. totorae) staminodal or lacking, the fertile anthers all subobliquely truncate, the orifice divided by a weak, sometimes obsolescent septum; ovary pilosulous overall, or only laterally, sometimes only residually, rarely glabrous; style (0.8-)1.3-2.7(-3.4) mm, at gently incurved apex 0.15-0.3 mm diam, the stigmatic cavity terminal; ovules (8-)10-22(-28). Pod obliquely pendulous, the stipe 2-8 mm, the straight or somewhat decurved, laterally compressed body 3.5-9.5 x 0.6-1.3(-1.5) cm, the stiffly papery, green then brownish, finely venulose glabrate valves variably turgescent over the seeds, the seed-locules 3-5 mm long, as wide as the pod’s cavity; seeds broadly or narrowly but always plumply obovoid or oblong-obovoid, little compressed, ±4-5.6 x 2.7-3.2 mm, the castaneous or atrocastaneous testa lustrous, smooth or rarely pitted.
Variety Key - Key to the Varieties of S. birostris 1. Anthers of 3 abaxial stamens all fertile, of ± equal length (4-7.8 mm) and girth even though the centric one is raised on a shorter filament than its neighbors; style 1.2-2.7(-3.4) mm. 2. Lfts glabrous on upper, often nearly so on lower face, the margins and the midrib on dorsal face ciliolate; widespread along the Andes from Ecuador to Argentina. 3. Plants of Peru s.-ward from 7°S, Bolivia and Argentina; filaments of longer abaxial stamens 3-11 mm; pod (0.75-)0.8-1.3(-1.5) cm wide. 4. Range extending from s. Bolivia (Potosi, Tarija) to San Luis in Argentina; lfts thick-textured glabrous minutely ciliolate; stipe of pod 2-4.5 mm. 110a. var. hookeriana (p. 339). 4. Range extending from n.-w. Bolivia through the Peruvian Andean plateau to An- cash and along its Pacific slope from Arequipa to La Libertad; lfts thin-textured if glabrous, often pubescent dorsally; stipe of pod 4.5-8.5 mm. 5. Sepals glabrous dorsally, not much graduated, the 2 outer (4.5-)5-7 mm, the longest inner one 6.5-8.5 mm; lfts subglabrous dorsally, only the midrib remotely ciliolate; Pacific slope of Peruvian Andes at 370-2000 m between La Libertad and Arequipa. 110f. var. birostris (p. 344). 5. Sepals either pubescent dorsally or some of them smaller, in either case well graduated; e. slope of Andes at ±2200-3500 m between n.-w. Bolivia and La Libertad, Peru, there and in Ancash passing the crest to the Pacific slope. 6. Sepals densely pilosulous dorsally, the inner ones relatively large, the longest 7-10.5 mm; Pasco, Huanuco, Ancash and La Libertad. 110e. var. helveola (p. 343). 6. Sepals glabrous or thinly pilosulous dorsally, shorter, the longest inner one 4.5-6.5 mm; Huancavelica and Cuzco, Peru and n.-w. Bolivia. 110c. var. huancavensis (p. 341).
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Discussion
Accumulated evidence has done nothing to strengthen the weak contrasts brought out by Bentham (1871) between Cassia hookerana, C. arequipensis and C. birostris, or by Macbride (1943) between the last two and C. helveola, which was from the first suspected of being no more than a "very pubescent form of one of the too closely allied species of the group." While they differ ideally, one from the next, in vesture, or in differentiation of the sepals, or in size and asymmetry of the androecium, or in ovule number, or in length, width and stipe of the pod, the character states are so subject to independent fluctuation that morphological discontinuities have become blurred or bridged. The species just mentioned, together with two entities hitherto undescribed, appear to form a replacement series distributed successively, mostly above 2000 m, along the Andean cordillera between latitude 33°S and the Equator, a series most realistically treated under one specific heading. Features characteristic of S. birostris in this wide sense are: narrow caducous stipules; ±6-14 pairs of leaflets veinless on the upper face; relatively small flowers (longest petal 7-14 mm); fertile anthers subsymmetrically truncate at apex; a pod variably stipitate and variably turgescent when ripe; and plump seeds lacking an areole. However, the complex specific concept that has been built up by accretion has incorporated so much variation that S. birostris sens. lat. cannot be separated from all relatives in a neat phrase. As a consequence we emphasize below only the diagnostic features of the constituent elements within the framework of their ecology and dispersal. The earliest specific epithet applicable to a member of this complex is hookeriana, mandatory in Cassia but unfortunately preoccupied in Senna. Next in seniority are the coeval birostris and arequipensis. We have chosen to maintain the former because of its longer history and aptly descriptive form. Key to the Varieties of S. birostris 1. Anthers of 3 abaxial stamens all fertile, of ± equal length (4-7.8 mm) and girth even though the centric one is raised on a shorter filament than its neighbors; style 1.2-2.7(-3.4) mm. 2. Lfts glabrous on upper, often nearly so on lower face, the margins and the midrib on dorsal face ciliolate; widespread along the Andes from Ecuador to Argentina. 3. Plants of Peru s.-ward from 7°S, Bolivia and Argentina; filaments of longer abaxial stamens 3-11 mm; pod (0.75-)0.8-1.3(-1.5) cm wide. 4. Range extending from s. Bolivia (Potosi, Tarija) to San Luis in Argentina; lfts thick-textured glabrous minutely ciliolate; stipe of pod 2-4.5 mm. 110a. var. hookeriana (p. 339). 4. Range extending from n.-w. Bolivia through the Peruvian Andean plateau to An- cash and along its Pacific slope from Arequipa to La Libertad; lfts thin-textured if glabrous, often pubescent dorsally; stipe of pod 4.5-8.5 mm. 5. Sepals glabrous dorsally, not much graduated, the 2 outer (4.5-)5-7 mm, the longest inner one 6.5-8.5 mm; lfts subglabrous dorsally, only the midrib remotely ciliolate; Pacific slope of Peruvian Andes at 370-2000 m between La Libertad and Arequipa. 110f. var. birostris (p. 344). 5. Sepals either pubescent dorsally or some of them smaller, in either case well graduated; e. slope of Andes at ±2200-3500 m between n.-w. Bolivia and La Libertad, Peru, there and in Ancash passing the crest to the Pacific slope. 6. Sepals densely pilosulous dorsally, the inner ones relatively large, the longest 7-10.5 mm; Pasco, Huanuco, Ancash and La Libertad. 110e. var. helveola (p. 343). 6. Sepals glabrous or thinly pilosulous dorsally, shorter, the longest inner one 4.5-6.5 mm; Huancavelica and Cuzco, Peru and n.-w. Bolivia. 110c. var. huancavensis (p. 341). 3. Plants of Ecuador; filaments of 3 abaxial stamens 2-3 mm; pod 0.6-0.7 cm wide. 110g. var. campiana (p. 345). 2. Lfts pilosulous on both faces and small (the longest 7-17 mm); Pacific slope of Andes from s.-w. Peru (Arequipa) to n. Chile (Tarapaca). 110d. var. arequipensis (p. 342). 1. Anthers of 2 lateral abaxial stamens fertile and 2.4-3.5 mm long, that of the centric one much smaller and sterile or the stamen absent; style 0.8-1 mm; e. edge of Bolivian altiplano in Cochabamba and Potosi. 110b. var. totorae (p. 340).