Senna silvestris

  • Title

    Senna silvestris

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna silvestris (Vell.) H.S.Irwin & Barneby

  • Description

    3.  Senna silvestris (Vellozo) Irwin & Barneby, comb. nov. Cassia silvestris Vellozo, Fl. Flum. 169, 1825.—Typus infra sub var. silvestri indicatur.

    Subshrubs, shrubs and trees, polymorphic in mature habit and stature, often precociously flowering when not or scarcely woody but potentially arborescent, at anthesis (0.5-)2-20(-30) m tall, varying from almost glabrous to densely strigulose, pilosulous or villous-tomentulose with commonly golden or rufescent hairs up to 0.1-0.6 mm, the membrano-chartaceous, moderately bicolored dull or lustrous foliage either glabrous or pubescent on either face, the inflorescence a corymbiform panicle or elongate thyrse of densely-fld corymbiform racemes.

    Stipules caducous, erect or incurved to erect, linear-setiform or subulate 4-8 x 0.5-1 mm, absent from most mature flowering and all fruiting specimens.

    Lvs (below the inflorescence) mostly 1.5-6 dm; petiole including wrinkled pulvinus 2.5-8 cm, at middle 1-2.3(-2.5) mm diam, subterete except for the very shallow open ventral sulcus; rachis (5-)8-30(-34) cm; petiolar glands 0; pulvinules 1.5-4.5(-6) mm; lfts (3-)4- 11 (-13) pairs, accrescent upward but usually only to a point beyond middle of rachis, thence often a little diminished, in outline symmetrically obovate-, oblong-, ovate- or lance-acuminate, obtuse mucronulate or acute, at base rounded or cordate, marginally revolute, the larger of fully developed lvs 4-13(-15.5) x 1.4-6(-6.5) cm, 1.8-4.5(-5.3) times as long as wide, the straight centric midrib depressed-sulcate above, cariniform beneath, the (8-)9-17(-18) pairs of camptodrome with random or alternating intercalary veins and subsequent venulation varying on upper face from subimmersed to finely prominulous, on the lower face from sharply delicately subprominulous to very strongly raised, then circumscribing sunken areoles.

    Racemes densely (7-)10-80(-105)-fld, the open fls elevated to or beyond level of succeeding buds, the axis scarcely elongating, together with stout spreading- incurved peduncle becoming (2-)2.5-16(-23) cm; bracts caducous from below very young fl-buds, ovate acute or lanceolate 1.2-2.5 mm; pedicels (excluding hypanthium) at and after anthesis (14-) 18-36(-40) mm; fl-buds obovoid or sub- globose, puberulent proximally or rarely puberulent up to periphery of inner sepals, these however ciliolate; hypanthium 2-3.5(-4) mm; sepals submembranous yellowish, brownish or livid with paler edges, concavely obovate-suborbicular or oblong-obovate, strongly graduated, the 2 outer 3.5-5.5 mm, the innermost (6.5-)7- 12(-13) mm, all early deflexed; petals glabrous yellow with darker yellow- orange veins or yellow with red flare at base, strongly clawed, subhomomorphic, their blades symmetrically broadly obovate or flabellate obtuse or widely emarginate, the longest (claw included) 13-23 (exceptionally 9-13) mm; androecium functionally 7-merous glabrous (the anthers rarely remotely pilosulous), the 3 staminodes linear, the filaments of 4 median stamens 2-3.5(-4.3) mm, of 3 abaxial ones (3.5-)4.5-7(-8) mm, those of the 2 long stamens dilated distally, the anthers all sagittate basally, those of 4 median stamens nearly straight 3-6 mm, their porrect biporose beak 0.6-1.2 mm, that of the centric abaxial stamen linear-lanceolate straight (3.5-)4-7.5 x 0.8-1.3(-l.5) mm, those of 2 latero-abaxial ones lunately lanceolate in outline (5-)6-10.5(-11) mm, at insertion of filament 1.3-2.2 mm diam, the often obscurely differentiated erect beak (0.5-)0.7-1.7 mm, its orifice divided by a slender septum; ovary either glabrous, pilose-ciliate along sutures, or pilosulous overall; style 2-4 mm, at apex incurved, slightly thickened (0.3-)0.35-0.7 mm diam, the stigmatic cavity introrsely lateral, minutely barbel- late; ovules 26-60.

    Pod obliquely declined or pendulous, the stipe 5-12 mm, cuneately expanded into the body, this linear or linear-oblong piano-compressed straight or slightly decurved (8-)10-27 x 1-3.3 cm, bicarinate by the scarcely thickened sutures, the glabrous or early glabrate, reddish or purplish-castaneous, often paler-margined valves becoming chartaceous or subcoriaceous ± lustrous, either finely or very coarsely venulose, low-corrugate over seeds, the transverse seed-locules either 1-seriate homomorphic oblong-elliptic in outline or 2-seriate and alternately oblong and bottle-shaped, the scarcely elevated septa 3-5.5 mm apart; seeds narrowly oblong or oblong-oblanceolate 5.3-8 x 2.3-3 mm, the brown, castaneous or atropurpureous testa smooth and lustrous, the shadowy and obscure or precisely differentiated areole linear or linear-elliptic 3-5 x 0.5-1.3 mm.

    Study of the extensive material that has accumulated in herbaria under the names Cassia sylvestris, C. lucens (or racemosa, misapplied) and C. sapindifolia demonstrates that the differential characters of number and outline of leaflets upon which Bentham principally relied to distinguish these species are no longer decisive, failing to coincide with morphological discontinuities or with patterns of dispersal. A search for more reliable criteria in the androecium or corolla merely confirms the fact, already perceived by Bentham, that granted some variation in size these are essentially uniform throughout ser. Sapindifoliae. The pod, of which Bentham had few samples, is now known to vary significantly in width, in texture and venulation of the valves and in alignment of the seeds; and the venulation of the leaves, more or less closely correlated with vesture, is closely linked to distribution. While Bentham’s three species have dwindled to fairly well-marked varieties, emphasis on some new criteria and the much more complete picture of dispersal built up in a century of collecting in South America enable us to define within a multiracial S. silvestris six infraspecific taxa. These cluster readily into two groups characterized by reticulation of the leaflet blades, one, the presumably more specialized subsp, bifaria, endemic to campo cerrado and related savanna communities in Brazil and adjacent Bolivia and Paraguay, the other, subsp, silvestris, primarily Hylaean but with disjunct representatives in coastal southeastern Brazil and the Paraguai valley.

    Review of the nomenclature in the light of our taxonomic decisions has brought to light a vexatious misapplication of the epithet silvestris, stemming probably from Vogel (1837, p. 36), but become traditional since Bentham’s monographs (1870, 1871). At this point we need only note that the genuine Cassia silvestris of Vellozo belongs properly to and, being older, must replace C. lucens Vog., the plant that Bentham, in another error (already corrected by Amshoff), called C. racemosa Mill. The taxon treated by Bentham as Cassia silvestris is technically undescribed; it appears here as S. silvestris var. bifaria. The points are discussed further below in the synonymy and commentary on vars. silvestris and bifaria. The emended spelling sylvestris of Vellozo’s epithet, first published by Vogel and later maintained by Bentham, has neither philological nor historical justification and should not be perpetuated.

    We are unable to refer to any particular variety of S. silvestris the fine portrait published in Flora Brasiliensis 15(2): t. 38, the model for it being unknown. As a generalized likeness of the species, sensu lato, it could hardly be improved, the details of corolla and androecium being especially lifelike. The leaves suggest our subsp, bifaria, the narrow pod containing about 30 seeds aligned in one row either var. unifaria or var. velutina.

    Key to the Subspecies and Varieties of S. silvestris

    1. Lfts glabrous above, either pubescent beneath (along major veins only or also between them) with straight appresssed or loosely ascending hairs, rarely glabrous on both faces; tertiary and subsequent venulation of dorsal face of lfts not so strongly raised as to form sunken areoles; Hylaean forest from Venezuela s. of the Orinoco and s.-e. Colombia to w.- centr. Bolivi, e.-centr. Paraguay and Mato Grosso, Brazil, thence interruptedly s. on the Atlantic slope in Brazil from e. Bahia to Sta. Catarina; subsp, silvestris:2. Lfts pubescent beneath, at least along secondary veins and midrib, and the larger ones mostly 7-13 cm, at base varying from cuneate to shallowly cordate, but if cordate the pulvinules 2.5-6 mm; ovules 36-60; Hylaean n.-ward from 17°S and disjunct along the Atlantic slope and coast between 13° and 27°S.3. Lfts of larger lvs (4-)6-11(-13) pairs, the largest 2-4 cm wide; range as above except for coastal Brazil in lat. 13-20°S.

    3a. var. silvestris (p. 89).3. Lfts of larger lvs (3-)4-5 pairs, the largest 3-6 cm wide; coastal forest of Bahia and Espirito Santo in lat. 13-20°S.

    3b. var. sapindifolia (p. 91).2. Lfts at once glabrous beneath and deeply cordate at base, the longest 4-7 cm, and their pulvinules only 1.5-2.2(-2.5) mm; s. Mato Grosso and e. Paraguay.

    3c. var. guaranitica (p. 91).

    1. Lfts finely (sometimes inconspicuously) puberulent above, densely pilosulous beneath with spreading, incumbent or curly hairs; tertiary and subsequent venulation of lower face of lfts sharply raised, circumscribing deeply recessed areoles; range entirely s. of, or in enclaves within the s. margin of, the Hylaean forest; subsp, bifaria:4. Large inner sepals golden-strigulose dorsally at the middle; pod 26-30-ovulate, the valves (±10-12 mm wide) chartaceous and finely venulose (like those of var. silvestris); middle Xingu, Tocantins and upper Parnaiba valleys in s.-e. Para, n. Goias and s. Maranhao in lat. ±7-9°S, s. in w. Bahia to ±13°S.

    3d. var. velutina (p. 93).4. Large inner sepals glabrous dorsally; pod 30-58-ovulate, the valves stiffly coriaceous, coarsely venulose; Brazilian Planalto and upper Paraguai valley in lat. 12-24°S.5. Pod 11-14 mm wide, 30-38-ovulate, the seed-locules 1-seriate, all alike oblong-elliptic; s. Mato Grosso and adjoining s.-e. Bolivia and Paraguay.

    3e. var. unifaria (p. 93).5. Pod 18-30 mm wide, 40-58-ovulate, the seed-locules biseriate, alternately shorter elliptic-oblong and longer bottle-shaped (the bottleneck accommodating the funicle); n.-e. Mato Grosso through highland Goias to n.-centr. Minas Gerais, thence s. to e. Sao Paulo.

    3f. var. bifaria (p. 94).