Senna oxyphylla

  • Title

    Senna oxyphylla

  • Author(s)

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna oxyphylla (Kunth) H.S.Irwin & Barneby

  • Description

    10.  Senna oxyphylla (Kunth) Irwin & Barneby, comb. nov. Cassia oxyphylla Kunth, Mimoses pl. 39. 1822 & p. 129. 1823.—Typus infra sub var. oxyphylla indicatur.

    Shrubs and treelets 1-7.5 m, the slender subterete branchlets as often also the lf-stalks, the dorsal face of lfts and the pod at least remotely and often densely resinous-punctate or -verruculose, the foliage and inflorescence varying from thinly strigulose with appressed hairs up to 0.2-0.4 mm to thinly or densely pilosulous with erect or loosely incurved hairs up to 0.3-0.65 mm, the lfts bicolored, dull or sublustrous olivaceous above, paler dull beneath, the inflorescence subcorymbose, paniculately corymbose or thyrsoid, either leafy at base, or leafy nearly throughout, or quite leafless, hence either exserted or not from foliage, its primary axis at maturity becoming abruptly flexuous.

    Stipules falcately oblanceolate-acuminate or linear, acute, 4.5-14 x 0.4-2 mm, when expanded arborescently venulose, usually caducous long before the lf, always deciduous before it.

    Lvs 7-17(-19) cm; petiole including scarcely swollen pulvinus (0.7-) 1-5.5 cm, at middle 0.7- 1.8(-2) mm diam, often a little dilated upward, openly shallow- sulcate ventrally; rachis (6-)9-37(-40) mm, either a little longer or shorter than petiole; gland between the proximal pair sessile or shortly stipitate, plumply ovate-linguiform obtuse or narrowly lanceiform acute 1.5-4 mm tall glabrous, a similar gland rarely between the distal pair, the seta caducous; pulvinules scarcely or moderately swollen, becoming finely wrinkled 2-4(-5) mm; distal pair of lfts varying independently in outline and asymmetry, commonly obliquely lance- or oblance-elliptic acute or acuminate (caudate), when relatively broad becoming obliquely ovate or obovate acute to shortly deltate-acuminate, those of larger lvs (4.5-)5-16 x 2-7 cm, 1.7-3.2(-3.6) times as long as wide, at base asymmetrially cuneate on both sides or (when broad) rounded to subcordate on proximal one, the margin revolute, the slender, usually incurved midrib with (6-)7- 13(-14) pairs of major camptodrome with or without intercalary secondary veins finely prominulous above, sharply cariniform beneath, the tertiary and reticular venulation prominulous on both faces or sometimes only beneath, the ultimate areoles variable in size, becoming smaller and more sharply defined with diminishing size of blade; proximal pair of lfts similar but often proportionately wider, as long as the distal.

    Peduncles with raceme-axis together (1.5-)2.5-11 cm; racemes densely (rarely loosely) 7-45-fld, at first subcorymbose; bracts either oblanceolate acute or lance- acuminate, (1.5-)2-6(-7) mm, usually caducous from below young buds, sometimes persistent into anthesis; pedicels at anthesis variable in length (sometimes on one raceme), (10-) 14-32 mm, but the fertile ones at least 20 mm and becoming in fruit thickened 22-36 mm; young fl-buds globose, puberulent at base or pilosulous throughout; sepals submembranous yellowish often red-flecked and hyaline-margined, delicately immersed-venulose, oblong-obovate, ovate or suborbicular, always very obtuse, little graduated, the innermost (4-)4.5-7 mm; petals yellow, puberulent externally along veins, variable in length and amplitude and sometimes moderately heteromorphic, up to 6-16 mm, the blades beyond the short claw obovate-suborbicular or oblong-oblanceolate, the 2 abaxial either a little shorter or a little longer but often a trifle narrower than the rest; androecium functionally 7-merous, the filaments either glabrous or puberulent, of 4 median stamens 1-2.5 mm, of 3 abaxial ones 2.5-3.5 mm, the anthers glabrous or puberulent along the dorsoventral grooves, those of 4 median stamens gently incurved 3.5-7 mm with divaricate blunt 2-porose beak 0.4-0.8 mm, those of 3 abaxial ones at once a little shorter, more strongly incurved and longer-beaked, the body 2.5-5.1 mm, the porrect beak (0.8-) 1-1.7 mm; ovary strigulose-pilosulous, the very short incurved style scarcely swollen, 0.6-0.9 mm diam just below oblique stigmatic orifice, this 0.3-0.4 mm diam; ovules (82-)90-146.

    Pod pendulous, the stipe 4-10 mm, the body subcompressed-terete, gradually narrowed at both ends, 11-27 x 1-1.2 cm, the valves green but brunnescent and glabrate, often resinously black-dotted, the sutures proper 1-2.5 mm wide, bordered on either hand by a thickened, smooth or papillose ridge 1-3 mm wide; dehiscence follicular, through the ventral suture, the valves finally explanate, the mesocarp tardily separating from the exocarp; seeds 2-seriate, turned broadside to the septa, embedded in thin pulp, obliquely ovoid-compressed 4.7-6.5 mm, the testa lustrous mahogany- or chestnut-brown, the areole 0 or represented by a faintly paler but not otherwise differentiated patch on either face of seed.

    This species, which we believe to be endemic to northern South America and not found, as Bentham thought, in Mexico or Central America, has always been difficult to define neatly or to separate from nearly allied ones; and so it remains, due partly to great internal variability and partly to the fact that its essential phenetic character, in context of ser. Bacillares, seems made up of negative qualities unredeemed by any feature peculiar to itself. In practice S. oxyphylla can be distinguished at anthesis from S. bacillaris by the smaller flower and revolute margin of the usually less asymmetric (and commonly smaller) leaflets; from S. viminea only insecurely by the zigzag primary axis of the mature inflorescence; from S. quinquangulata either by lack of a distal petiolar gland or by this combined with a slender style; and from sympatric races of 5. papillosa or S. dariensis by the smaller abaxial anthers (the body excluding beak 2.5-4 not

    4+ mm). The two last are handily distinguished in fruit, the first by its narrow, densely papillose pod and the second by its narrow, laterally compressed one, both of them lacking thickened borders parallel to the suture. Pods or S. oxyphylla and S. bacillaris are similar in external form, but here the seeds diner materially, those of S. bacillaris having a marked areole, lacking in the other. Both pod (lacking borders) and seed (with areole) distinguish allopatric S. fruticosa which we have not been able to distinguish by any one reliable feature of the flowering plant.

    In Venezuela S. oxyphylla is highly variable in pubescence, and the synonymy reflects an exaggerated emphasis in the past on this feature. The ranges of ap- pressed-pubescent or glabrate and of pilosulous or densely villous-pilosulous states are approximately the same, but we lack field data about possible correlation of these states with local edaphic conditions. Flowers produced early in the season are mostly axillary and immersed in foliage, but give way to a depauperately leafy or naked panicle later in the year. Although first described as a tree 50 feet tall, S. oxyphylla has been encountered since only as a shrub, treelet or sarmentose bushrope flowering at heights of two to five, exceptionally seven meters.

    The range of typical S. oxyphylla is more or less continuous along the crest and north slope of Venezuela’s coastal mountains from Sucre west to Maracaibo Basin, extending thence feebly south along Cordillera de Merida to Portuguesa and along the eastern Andes in Colombia to Norte de Santander. Remotely disjunct populations confined to the Pacific lowlands around Guayaquil Bay in Ecuador, one of which furnished the type of Cassia hartwegii Benth., seem certainly conspecific in the wide sense but differ in enough small details to deserve some taxonomic notice. Part of the gap in the whole dispersal of S. oxyphylla is occupied by the still obscure entity described herein among imperfectly known species as Chamaefistula toroana; it very possibly may eventually rank as a third geographic expression of the species.

    Key to the Varieties of S. oxyphylla

    1. Stipules mostly expanded and 0.6-2 mm wide; anthers of 3 abaxial stamens small, the body (below beak) 2.5-4 mm; borders parallel to the pod’s sutures smooth; n. Venezuela and n.-e. Colombia.

    10a. var. oxyphylla (p. 120).

    1. Stipules linear-setiform 0.3-0.5 mm wide; anthers of 3 abaxial stamens longer, the body 4.3-5 mm; thickened borders parallel to the pod’s sutures densely papillose.

    10b. var. hartwegii (p. 121).