Senna rizzinii

37.  Senna rizzinii Irwin & Barneby, nom. nov. Cassia granulata Rizzini, Leandra 4-5: 16. 1974.—. . ad Paulo Afonso, Bahia, in Caatinga ... A. P. Duarte XII-73."—Holotypus not seen, but the protologue conclusive.—Non C. granulata (Urban) Macbride, 1919.

Cassia chrysocarpa var. (?) psilocarpa Bentham in Martius, Fl. Bras. 15(2): 101. 1870.—.. in collibus arenosis prope Aracaty provinciae Ceara: Gardner n. 1568."—Holotypus, collected VII. 1838 (fl, fr), K! = IPA Neg. 907.

Shrubs 1.5-4 m, pilosulous almost throughout with fine short incumbent and scattered longer, loosely ascending hairs up to 0.35-0.7 mm, the hornotinous branchlets terete or bluntly angled, the small foliage bicolored, the lfts sublus- trously olivaceous above, paler dull beneath, usually pubescent on both faces and the hairs on upper face pustulate-dilated at base, sometimes glabrescent ventrally, the inflorescence thyrsoid-paniculate, the lower racemes often leafy- bracteate but the distal naked and well exserted.

Stipules very slenderly pliantly setiform (2-)3-7 mm, at base 0.25-0.45 mm wide, tardily deciduous with or after the lf.

Lvs 3-7 cm; petiole including discolored but scarcely swollen pulvinus (7-)l 1-26 mm, at middle 0.4-0.8 mm diam, obscurely shallow-sulcate; rachis 4-9 mm; gland 1 between proximal pair, stipitate, slenderly claviform acute 1.1-2.6 x 0.3-0.6 mm, pilosulous at least at base; distal pair of lfts asymmetrically elliptic, lance-, or ovate-elliptic obtuse or subacute mucronulate (18-)20-45 x (7—)9—15 mm, ±2-3 times longer than wide, at base cordate on proximal and cuneate on distal side, the margin revolute, the slender straight or gently incurved midrib with 5-9 pairs of camptodrome secondary veins all prominulous on both faces but very finely so above, more sharply so beneath, the tertiary venulation faint and irregular or immersed.

Peduncles with raceme-axis 2-8 cm, the peduncle 0.7-1.8 cm, the raceme rather densely 7-20-fld; bracts firm, yellowish or brownish, elliptic or obovate-elliptic acute 4-7(-10) x 2-4(-8) mm, at base embracing the pedicel, deciduous at full anthesis or subpersistent; pedicels 10-18 mm; buds globose, thinly pilosulous or glabrate; sepals yellowish, the outer elliptic-obovate 5-6 mm, the inner subpetaloid broadly oblong-obovate or suborbicular 7-9 mm; petals yellow, pilosulous dorsally, scarcely heteromorphic, oblong-obovate beyond the slender claw, the longest (10.5-) 14-19 mm; filaments thinly puberulent, of 4 shorter fertile stamens 1.2-2 mm, of 3 long abaxial ones 2.5-5.5 mm; thecae glabrous or thinly pilosulous in dorsoventral grooves, of 4 shorter median stamens 5-5.5 mm, with divaricate beak 0.45-0.6 mm, of 3 longer ones 5-6 mm, with porrect beak 0.6-1.2 mm; ovary densely shaggy-pilosulous, the less densely pubescent style 4-5 mm, gently incurved and 0.45-0.75 mm diam at apex, the stigmatic aperture 0.3-0.4 mm diam; ovules 44-58.

Pod stiffly ascending or geotropic, long-persistent in papery tatters after discharge of seed, the stipe 2-6 mm, the body plumply sausage-shaped terete ±3.5-8.5 x 1.1-1.7 cm, abruptly contracted at both ends, the thin valves becoming papery castaneous and ultimately blackish, at first thinly or remotely pilosulous, then glabrate; seeds biseriate, compressed-obovoid, ±5.5-6 x 3.1-3.5 mm, the testa blackish-brown, brilliantly lustrous, crackled, exareolate.—Collections: 26.

Caatinga, disturbed semideciduous woodland and cerrado, sometimes on stabilized dunes near the coast, from near sea-level n.-e.-ward but up to 1000 m in Bahia, scattered over n.-e. Brazil from s. Ceara e. to interior e. Paraiba, s. to n. and e.-centr. Bahia e. of Rio Sao Francisco (possibly adjacent Alagoas), on Chapada Diamantina extending s. to Sa. Agua da Rega and the middle Paraguaçu valley; apparently disjunct, in a possibly distinct, as yet poorly known form, on coastal dunes of Ceara and Paraiba.—Fl. (XII-)I-VI.

Senna rizzinii closely resembles S. chrysocarpa, which see for differential commentary. In general habit and details of the foliage it is also uncomfortably similar to partly sympatric S. macranthera var. pudibunda. The mature pedicels of var. pudibunda are longer (2.5-5, not less than 2 cm), its petals when fully expanded are longer (up to 22-30, not 14-19 mm), the dimorphism of its fertile stamens is more pronounced, and its relatively many-ovulate gynoecium ripens to a longer pod. A feature common to both is a relatively long style (3-5 mm) and both are adapted to a seasonally arid regimen. Collectively these two entities go far to bridge the morphological gap between S. chrysocarpa and S. macranthera sens, lat., species traditionally referred to different groups because of the androecial differences. The technical characters of S. rizzinii and S. macranthera var. pudibunda need careful field-study in northern Bahia, flowers and fruits from the same populations, up till now not available for comparative study, being especially wanted.

In lieu of the holotypus we have taken as representative of Cassia granulata specimens from the type-locality, between Alagoas and Paulo Afonso, A. P. Duarte 14180, NY, RB, which correspond closely with the description.