Senna rupununiensis

  • Title

    Senna rupununiensis

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna rupununiensis H.S.Irwin & Barneby

  • Description

    33.  Senna rupununiensis Irwin & Barneby, sp. nov., petiolo 2-glanduloso sepalisque late obovato-suborbicularibus S. lourteigianae et S. undulatae propiuscula, a priori foliolis angustioribus basi asymmetricis, mflores- centiae axibus petalisque dorso puberulis necnon legumine tereti (nec argute 4-angulo), a secunda imprimis bracteis floralibus parvis angustis (nec dilatatis sepaloideis) ulterius sepalis magnis (interioribus 10-12 nec 6—8.5 mm longis) breviter tantum (nec diu) ante anthesin expansis manifeste diversa.—GUYANA: near mouth of Charwair Creek, basin of Rupununi River, near 2°35'N, 1-4.XI. 1937 (fr), A. C. Smith 2358. Holotypus, NY; isotypi, F, G, K, MO, US. BRAZIL. Terr, do Ro- raima: Boa Vista, Rio Branco, VII. 1913 (fl), J. G. Kuhlmann s.n. in RB 3232—Paratypus (fl), NY.

    Vines of unknown length, with terete, in age obtusangulate and pallid branchlets, the lower face of the chartaceous lfts and the inflorescence strigulose-pilosulous with subappressed-incumbent hairs up to 0.1-0.25 mm, the foliage bicolored, lustrous olivaceous and sharply venulose above, pale dull and smooth or almost so beneath, the inflorescence of racemes axillary to living lvs or forming a small terminal leafless panicle, this sometimes well exserted from foliage.

    Stipules erect firm linear-attenuate 2.5-7 x 0.4-0.5 mm, deciduous.

    Lvs 6-12 cm; petiole slender 1.5-3.5 cm, at middle 0.7-1 mm diam, obtusely triquetrous, keeled dorsally, openly shallow-sulcate ventrally; rachis (0.7-) 1-2 cm, shorter than petiole; glands between both pairs of lfts, sessile or shortly stipitate, 2-3 mm tall, the head ovoid or claviform glabrous livid; distal pair of lfts narrowly elliptic-oblanceolate, elliptic, or rarely ovate, obscurely short- acuminate, at very apex obtuse mucronulate or minutely retuse, (4.5-)5-8.5 x (1-) 1.3-3.2 cm, 2-4.5(-5.4) times longer than wide, at very base asymmetrically broadly cuneate, the margins revolute (not undulate), the gently incurved midrib bluntly prominulous above, cariniform beneath, the ±10-16 pairs of camptodrome and intercalary secondary veins with tertiary and reticular venulation all strongly prominulous above, faintly so or almost immersed beneath; proximal pair of lfts similar, 1/2-3/4 as long, proportionately scarcely broader or more oblique.

    Racemes 3-10-fld, the axis with peduncle becoming 1-8 cm; bracts firm lance- ovate acute 3.5-5.5 x 1.2-1.8 mm, persistent into anthesis but then deciduous; pedicels 16-28 mm; buds globose, thinly puberulent when young, the inner sepals glabrate, these shielding the androecium until shortly before true anthesis; sepals yellowish petaloid-margined, broadly spatulate-obovate or suborbicular, moderately graduated, the outermost 7-8, the inner up to 10-12 mm; petals yellow, puberulent dorsally, beyond slender claw flabellate-obovate subhomomorphic except the adaxial one broadest, the longest up to 16-19 mm; functional androecium 7-merous, the filaments thinly puberulent, those of 4 median stamens ±1.5 mm, those of 3 abaxial ones 3-4 mm, the anthers glabrous, those of 4 median stamens nearly straight 6.5-7.5 mm, with very short divaricate 1- or 2-porose beak, those of 3 abaxial ones slightly more incurved 6-7 mm, with almost erect beak ±1.5 mm; ovary densely strigulose; style very short, not dilated, near apex 0.8 mm diam; ovules ±100.

    Pod pendulous short-stipitate, the stout stipe ±3 mm, the cylindric (by abortion of ovules irregularly constricted or deformed), slightly incurved body 8-12 x 1.3-1.5 cm, the sutures apparently without thickened margins, the stiffly coriaceous valves becoming brown smooth or coarsely low-venulose; dehiscence follicular, along the ventral suture; seeds biseriate, turned broadside to the septa, broadly compressed-ovoid 4.5-5.3 x 3.2-4.2 mm, the testa mahogany-brown, highly lustrous, cross-crackled, exareolate.—Collections: 3.

    Thickets on savanna and margins of gallery forest, ±250-300 m, apparently localized on and near the Rio Branco-Rupununi divide in n.-e. Territorio do Roraima, Brazil (near Boa Vista) and adjoining Guyana (Charwair and Sand creeks).—Fl. VII-IX.

    The fruiting type-collection of S. rupununiensis was identified as an unnamed relative of S. undulata, from which it differed obviously in the narrowly elliptic, almost willow-like leaflets, a character now known not to be truly diagnostic (see Wilson-Browne 137, K, with ovate leaflets). Flowering material which we confidently associate with Smith’s fruiting typus shows the species to differ gravely from S. undulata in the small firm (not large sepaloid and colored) floral bracts and in substantially larger sepals which remain closed over the androecium, like those of S. latifolia, until immediately before true anthesis of the flower. In details of the flower S. rupununiensis resembled the equally localized S. lourteigiana, which is readily distinguished, however, by the broader, basally symmetrical leaflets glabrous and venulose on both faces, the glabrous inflorescence and petals, and the peculiar quandrangular pod. Marginally sympatric S. latifolia, which has as already noted almost the sepals of S. rupununiensis and can, very occasionally, have a gland between the distal as well as the proximal pair of leaflets, is more readily separable by the much larger plane-margined, not conspicuously revolute leaflets.