Senna williamsii

  • Title

    Senna williamsii

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna williamsii (Britton & Rose) H.S.Irwin & Barneby

  • Description

    167.  Senna williamsii (Britton & Rose) Irwin & Barneby, comb. nov. Peiranisia williamsii Britton & Rose, N. Amer. Fl. 23(4): 265. 1930.—"Type from Bismark, above Penomene, 2000-3000 ft elevation, Panama, March 18, 1908, R. S. Williams 567."—Holotypus, NY! isotypi, NY = NY Neg. 9398, US!—Cassia williamsii (Britton & Rose) Standley, Field Mus. Bot. 18(Fl. Costa Rica): 519. 1937.

    Cassia williamsii sensu Schery, 1951, p. 70, fig. 126.

    Weakly arborescent shrubs 2-3.5 mm with trunk up to 3.5 cm diam and subterete annotinous branchlets densely leafy distally, these with ventral angle of lf- stalks pilosulous with fine spreading-incumbent pallid hairs up to 0.1-0.2 mm mixed with minute thickened orange or livid trichomes, the stems in addition nearly always hispid with stiff lustrous white setae 4.5-9 mm, the very numerous small lfts subconcolorous glabrous, the corymbose-paniculate inflorescence composed of shortly or subumbellately few-fld racemes arising from axils of coeval lvs and shorter than them.

    Stipules herbaceous, falcately lance-attenuate 5-12 x 1-2 mm, deciduous.

    Lvs 9-22 cm; petiole including little-swollen pulvinus (8-) 11-22 mm, at middle 0.6-1.2 mm diam, bluntly narrow-margined and shallowly sulcate ventrally; rachis 7.5-19 cm; glands between proximal (1-)2-3 pairs stipitate, in profile (1.6-)2-4.2 mm, the fusiform acute body 0.3-0.6 mm diam, between all other pairs a much shorter and narrower acicular gland; lfts 36-63 pairs, inserted 1.5-3.5(-4) mm apart along rachis, very gently decrescent both up- and downward from near or below middle, pitched forward from rachis on pulvinule 0.4-0.8 mm, the blades of larger ones linear-oblong from asymmetrical base, obtuse mucronulate, 7-16 x 1.3-2.5 mm, ±4.5-6 times as long as wide, the smaller distal ones often linear-oblanceolate and proportionately wider, all appearing veinless except for slender centric midrib prominulous beneath, a secondary venulation of 5-7 pairs of camptodrome nerves sometimes faintly discolored beneath but fully immersed.

    Peduncles 1-5 cm; racemes (2-)3-7-fld, the axis 1-10 mm; bracts submembranous lanceolate 2.5-5.5 mm, caducous; pedicels 18-32 mm; buds globose glabrous; sepals strongly graduated, the 2 inner ones obovate-suborbicular 10-14 mm; petals glabrous, except for one all obovate to broadly oblanceolate beyond the slender claw, the odd abaxial one obliquely or falcately lanceolate, the longest 23-29 mm; androecium glabrous, the filaments of 4 median stamens 1-1.7 mm, those of 3 abaxial ones 1.5-3 mm, the anthers of 4 median stamens 5-5.5 mm, gently incurved, the very short biporose beak lateral, those of 3 abaxial stamens slightly more incurved 5-5.7 mm, the porrectly erect biporose beak 0.9-1.5 mm; ovary puberulent; style 2-2.5 mm, near apex 0.35-0.4 mm diam; ovules 36-44.

    Stipe of pod 5-6 mm, the narrowly linear straight compressed body 10.5-15 x 0.33-0.48 mm, the interseminal septa 2.5-4(-4.5) mm apart, the seed cavity as long or longer than width of valves; seeds rhombic-obovate 2.6-3.4 mm, the testa pale brown dull, the oblong-elliptic areole 1.3-1.5 x 0.5-0.6 mm.—Collections: 10.

    Habitat little known, sometimes in disturbed rainforest ±550-950 m, scattered along the Pacific slope of the Continental Divide from s.-e. Costa Rica (Cordillera de Talamanca) through Chiriqui to Code (Valle de San Anton; Penonome) and Panama (Cerro Campana) in Panama.—FI. XI—III.

    A highly ornamental senna, closely akin to S. mutisiana, which see for commentary. The proportionately narrow, pluriovulate pod distinguishes the species from otherwise comparable Interglandulosae. Schery’s figure (l.c.) incorrectly shows some flowers solitary in leaf-axils.