Senna uncata

Title

Senna uncata

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Senna uncata H.S.Irwin & Barneby

Description

50.  Senna uncata Irwin & Barneby, sp. nov., petiolis brevissimis, perianthii an- droeciique forma et imprimis racheos seta indurata vulneranti S. cornigerae manifeste affinis sed ab ea habitu arborescenti (nec scandenti), foliorum (superiorum tantum notorum) breviorum 6-13 (nec 10-20) cm longorum rachi abbreviato 1-2.3 (nec 4-5.5) cm longo foliolisque dis- talibus parvis 4.5-9.5 (nec 10-14) cm longis plano-marginatis (nec re- volutis), seta indurata abrupte uncato-recurvata (nec prorsus patula), sepalo interiori maximo minori ±10 (nec 11-15) mm longo, patriaque remotissima peruviana dispar.—PERU. Amazonas: Quebrada Chichi- jam Entsa, monte, 1100 ft [±330 m], 24.IV. 1973 (fl), Ernesto Ancuash 289.—Holotypus, NY; isotypus, MO.

Arborescent vines of unknown stature, the flowering branchlets stout stiff terete striate, the young parts and axes of inflorescence strigulose with incumbent hairs 0.1-0.2 mm, the lfts bicolored, dull brownish-olivaceous glabrous above, paler dull and densely puberulent beneath, the inflorescence elongately thyrsiform-paniculate, distally exserted from foliage.

Lvs at base of inflorescence 6-13 cm, those lower on stems unknown (perhaps larger); petiole including shrunken pulvinus 8-13 mm, at middle 1.2-2.4 mm diam, obscurely shallow-sulcate; rachis 10-28 mm, longer than petiole, produced beyond the distal pair of lfts as a rigid, backwardly arcuate, vulnerantly acute hooklike seta 4-8.5 mm; gland 1 sessile between proximal pair of lfts, plumply ovoid obtuse 3-4.5 x 1.8-3.3 mm glabrous; pulvinules 3-5.5 mm; distal pair of lfts symmetrically ovate abruptly obtusely short-acuminate 4.5-9.5 x 3-5.4 cm, 1.3-1.7 times as long as wide, at base equilaterally shallow-cordate, the margin plane but ± undulate, the straight centric midrib impressed on upper and cariniform on lower face, the 8-12 major camptodrome secondary with connecting tertiary venulation finely prominulous on both.

Racemes solitary or rarely geminate, ±7-20-fld, the axis including stout, stiffly erect peduncle 5-12 cm; bracts ovate-elliptic or -deltate 1.5-2.5 mm, early dry and deciduous at or soon after anthesis; pedicels at anthesis 3-3.5 cm; buds nodding globose, glabrous except at very base; sepals strongly graduated, the outermost ± half as long as the innermost, all submembranous, delicately venulose, broadly obovate-suborbicular, the largest ±10 mm; petals exactly of S. cornigera, the adaxial one 23-25 mm; functional stamens 7, the filaments thinly puberulent, those of 4 median and 1 abaxial 2-2.5 mm, swollen distally, of 2 abaxial 4-5.5 mm, the anthers glabrous or nearly so, those of 4 median stamens slightly incurved 6-7.5 mm with divaricate 2-porose beak ±0.5 mm, those of 3 abaxial ones lunately incurved 12.5-14.5 mm with porrect beak 1—1.3 mm, two of them cupped in an abaxial petal; ovary densely gray-strigulose; style scarcely dilated, ±0.7 mm diam just below stigma, the orifice 0.2 mm diam; ovules ±124.

Pod geotropic, the stout stipe ±1 cm, the body up to 30 x 1 cm, laterally compressed but up to 0.5 mm thick, in cross section oblong-elliptic, the broad sutures 2-3 mm wide, undulately depressed between seeds, the faces low-convex, the thin-textured valves becoming purplish-brown, closely investing the seeds, apparently at length breaking transversely along the septal lines; seeds 1-seriate, turned broadside to the septa, in wider profile ±9 x 5.5 mm, 3 mm thick, the lustrous castaneous testa crackled, exareolate.—Collections: 2.—Fig. 19.

In the virgin monte at 200-350 mm, apparently rare, known only from the middle Maranon and lower Santiago valleys in Amazonas, Peru.—Fl. IV-V. Tam-push; naek tampush.

Due to paucity of collections our accounts of S. uncata and S. cornigera are obviously incomplete, and firm differential characters can only emerge as the species become better known. Together with S. acuparata they are distinguished from all other Bacillares by the modified seta of the leaf-stalk, a shared feature which, reinforced by essentially similar flowers, suggest a close relationship. While the setae are homologous, they differ in form, that of S. cornigera being turned back at right angles from the leaf-stalk and its tip lifted a trifle forward, whereas that of S. uncata is abruptly recurved into a grappling hook. We have seen of each only leaves associated with the thyrsiform panicle, but these are shorter in S. uncata, the pairs of leaflets are separated by a shorter rachis, and the blade-margins are undulate but not revolute as in S. cornigera. The known ranges of the two species stand about 2800 km apart near opposite margins of the Amazonian Hylaea. Comparison of the pods must await discovery of that of S. cornigera. In general morphology and arrangement of the seeds the pod of S. uncata resembles that of S. georgica but is nearly twice as wide.