Senna weddelliana

  • Title

    Senna weddelliana

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna weddelliana H.S.Irwin & Barneby

  • Description

    103.  Senna weddelliana Irwin & Barneby, sp. nov., affinitatis fructu ignoto in- certae sed adspectu toto S. lasseignianam arete simulans et quoad pube, stipulas aliasque notulas ei vero simillima, sed foliolis lanceo- lato-acuminatis nec ellipticis, anthera centrica abaxiali cassa necnon ovulis minus numerosis ±15-18 (nec 28+), ulteriusque patria procul aliena certe diversa.—BOLIVIA. Cochabamba: Liriumi, 2570 m, III. 1946 (fl), M. Cardenas 3636.—Holotypus, US 1564478 = NY Neg. 10597.

    Shrubs and slender trees at anthesis 1.5-4 m, the terete brown hornotinous stems, lf-stalks and axes of inflorescence pilosulous with erect or widely ascending yellowish hairs up to 0.35-0.55 mm, the ample thin-textured foliage bicolored, the lfts above dark green puberulent or glabrate, beneath paler and charged with minute thickened orange trichomes mixed with soft weak hairs, the inflorescence of racemes at first axillary to and surpassed by lvs, these becoming smaller distally and the latest racemes often paniculate and shortly exserted.

    Stipules reflexed, thinly herbaceous or submembranous, lanceolate plane 3.5-6 x 0.7-1.2 mm, early dry deciduous.

    Lvs 7-19 cm; petiole including the wrinkled pulvinus 2.5-6 mm, sometimes reduced to the pulvinus itself, 1-1.5 mm diam; rachis (4-)5-11 cm, bluntly narrow- margined and openly shallowly sulcate ventrally, the longer interfoliolar segments 15-22 mm; glands between proximal only or sometimes also between 1-2 succeeding pairs of lfts, sessile or substipitate, in profile 1-1.6 x 0.5-0.7 mm, the body ovoid-acuminate or obpyriform; lfts 4-6 pairs, strongly accrescent distally, all broadly lance-acuminate, the distal pair 4-8 x 1.1-2.3 cm, 3.2-4 times as long as wide, at very tip abruptly acute mucronulate, at base cordate or broadly rounded on proximal and rounded or broadly cuneate on distal side, the margin strongly revolute, the centric midrib depressed-sulcate above, cariniform beneath, the ±9-12 pairs of slender camptodrome with faint random intercalary secondary veins delicately raised beneath only, subsequent venulation immersed.

    Racemes densely ±15-35-fld, the 2-several simultaneously expanded fls raised to level of the crowded spreading-ascending, densely pilosulous subglobose fl- buds, the axis with peduncle together 5-11 cm; bracts submembranous lance- acuminate 4-8 x 0.8-2 mm, early dry, deciduous before or by anthesis; pedicels at anthesis very slender 16-25 mm; sepals obovate subpetaloid, yellowish faintly veined, moderately graduated, the firmer outermost one 3.5-4.5 mm, the largest dorsally glabrescent inner one 5-6.5 mm; petals glabrous orange-yellow drying pale yellow delicately brown-veined, zygomorphic, the vexillary one widest obcordate, the longest 8-12 mm; androecium glabrous, functionally 6-merous, the filaments of 4 median and the centric abaxial stamens 2-2.5 mm, of the 2 long abaxial ones 3.5-4 mm, the anthers brown, those of 4 median stamens straight obliquely truncate 2.7-3.2 x 0.8-0.9 mm, of the centric abaxial one sterile 2.5-3 x 0.4-0.6 mm, of two long abaxial ones 3.5-4.8 x 1-1.2 mm, subhorizontally truncate at apex, 2-porose; ovary rather thinly pilosulous; style glabrous linear 1.8-2 x 0.2 mm, incurved from ovary but straight or almost so distally, the stigmatic cavity terminal; ovules (2 counts) 15-18.

    Pod and seeds unknown.—Collections: 3.

    Moist forested hillsides near 2500-2700 m, apparently local on headwaters of Rios Beni and Mamore in Cordillera de Cochabamba, near 17°S, in centr. Bolivia.—Fl. XII-III.

    Senna weddelliana has been compared in our diagnosis with S. (Coluteoideae) lasseigniana, superficially similar, but is nevertheless provisionally assigned to a different series on account of the low ovule number which in all probability foretells a compressed pod and seeds broadside to the valves appropriate to ser. Pachycarpae. Within its range of dispersal it will be readily recognized by the syndrome of ample subsessile leaves, 4-6 pairs of broadly lance-acuminate, marginally revolute leaflets, small brachystylous flower and 15-18-ovulate pistil. Its systematic relationships will not be ascertained until the pod and seed are known. The species is named in memory of Hugh Algernon Weddell, who first collected it on Rio Ayopaya in December 1846.