Senna praeterita

  • Title

    Senna praeterita

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna praeterita H.S.Irwin & Barneby

  • Description

    108.  Senna praeterita Irwin & Barneby, sp. nov., S. mandoni et S. cruckshanksii ut videtur affinis, ab ilia, quoad folia, antherarum formam ovulo- rumque numerum congrua, praesertim floribus minoribus (petalo maximo ±7.5 nec 9.5-14 mm longo) styloque abbreviato vix incurvo (nec hamato), ab hac foliolis exacte 3 (nec 4-5)-jugis margine tenui planis, antheris breviter infra apicem constrictis necnon ovulis ± 16 (nec 9-11), ulterius ab ambabus patria distantissima certe diversa.—PERU: Amazonas: Sesuya, Chachapoyas, anno 1840, Andrew Mathews 3276.— Holotypus, K (hb. Hook.) = NY Neg. 10631; isotypus, BM.

    Shrubs of unknown stature, with terete striate, at length purplish and fissured hornotinous branchlets, except for rudimentary puberulence of stem and pulvinules and for sparingly ciliolate bracts glabrous throughout, the foliage bicolored, the lfts dull green above, pallid glaucescent beneath, the inflorescence a terminal subcorymbose, shortly exserted panicle of racemes.

    Stipules linear-lanceolate ±4-6 x 0.5-0.7 mm, caducous.

    Lvs 6-9.5 cm; petiole including dilated pulvinus 1.8-3 cm, narrowly sulcate ventrally; rachis 2-3 cm; gland between the proximal and sometimes also the second pair of lfts, including its short stipe 2-2.6 mm tall, the narrowly oblong- ellipsoid body 0.4-0.7 mm diam; lfts exactly 3 pairs, strongly accrescent distally, the distal pair broadly elliptic emarginate 2.7-4.2 x 1.2-2.1 cm, 1.8-2.3 times as long as wide, at very oblique base semicordate on proximal and cuneate on distal side, the membranous margin plane, the slender centric midrib immersed above, finely prominulous beneath, the 7-9 pairs of secondary veins either weakly raised or immersed and discolored, tertiary venulation imperceptible.

    Peduncles from distal axils 3.5-5 cm; racemes loosely 6-18-fld, the expanded fls raised to level of nodding glabrous globose buds, the axis by late anthesis ±1-3 cm; bracts submembranous, narrowly lanceolate 3.5-5 x 0.5-0.8 mm, persistent into anthesis, then deciduous; pedicels (fertile) becoming ±2 cm; sepals submembranous, fuscous broadly pallid-margined, moderately graduated, the outermost ovate ±3.5-4.5 mm, the innermost obovate ±5-6 mm; corolla zygomorphic, the petals glabrous, yellow drying whitish dark-veined, all obovate or the vexillary one obcordate, of subequal length, ±7.5 mm; androecium glabrous, the obtusely quadrate staminodes 1-1.4 mm diam, the filaments of 4 median stamens 1.2-1.5 mm, of 2 exterior abaxial ones 2.5 mm, of the centric abaxial one ±2 mm, the anthers brown, the 4 median 3-3.3 x 0.9-1 mm, little incurved, the 3 abaxial lunately incurved 4.5-5.5 x 1.1-1.2 mm, all gently constricted 0.5 mm below apex and thence a trifle expanded into the subhorizontally truncate orifice, this divided by a slender septum; ovary glabrous; style slightly incurved, 1.2-1.5 x 0.15-0.2 mm, the minute stigmatic orifice looking upward; ovules 16.— Collection: 1.

    Habitat not recorded, to be expected in thickets or woodland margins, known only from the type-locality in Amazonas, Peru.—Season of bloom unknown.

    The type-collection of S. praeterita was examined by Bentham who passed it over with the remark, in annotation, that it resembled Cassia bicapsularis but differed in its bracts and in its small flowers. It was incautiously reidentified by a recent student as C. pendula var. pendula. The low ovule-number, 16 in one flower examined, prefigures a piano-compressed pod of a type seen in the habitally similar S. mandoni, and is incompatible with any close kindred of S. bicapsularis or S. pendula. We suppose S. praeterita to be related to S. mandoni, from which it differs (at anthesis) in the smaller flower and especially in the short, very slightly incurved and not distally hooked style. At anthesis S. praeterita is suggestive of S. cruckshanksii, but the strictly plane leaflets, apparently stabilized at exactly three pairs, the apically constricted anthers and the rather more numerous (16, not 9-11) ovules are differential characters which we confidently expect will be reinforced by comparison of the pods. The fundamentally different dispersal and (presumably) ecology of S. praeterita, on a source of the Amazon in equatorial latitudes (near 6°S), and S. cruckshanksii, in the Mediterranean climate of central Chile, preclude any chance of them proving conspecific.