Senna polyphylla

  • Title

    Senna polyphylla

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Scientific Name

    Senna polyphylla (Jacq.) H.S.Irwin & Barneby

  • Description

    169.  Senna polyphylla (Jacquin) Irwin & Barneby, comb. nov. Cassia polyphylla Jacquin, Collectanea 4: 104. 1791.-Typus infra sub var. polyphylla indicatur.

    Stiffly much-branched microphyllous shrubs and treelets at anthesis 1.5-8 m, with long, densely leafy, widely ascending, horizontal or geotropic branches, the young branchlets and lf-stalks commonly strigulose-pilosulous with appressed or widely ascending pallid hairs to 0.2-0.4(-0.5) mm, sometimes subglabrous, the small firm leaflets commonly glabrous but sometimes thinly pubescent beneath and ciliolate, on both sides olivaceous brunnescent but a little paler beneath, the lvs dimorphic, the longer primary ones subtending condensed brachyblasts or spurs clad in fasciculate shorter lvs mixed with 1-3-fld peduncles, the longer lvs early deciduous, the inflorescence thyrsiform, the relatively large and showy fls exserted from the small foliage.

    Stipules (of primary lvs) erect, subulate-setaceous 2-5.5 mm, tardily deciduous, those of spur-lvs shorter, more persistent.

    Lvs of primary nodes of long-shoots solitary 1.2-5.5(-6) cm; petiole including moderately dilated pulvinus 2-5.5(-6.5) mm, at middle 0.45-0.7 mm diam, rounded dorsally, openly sulcate ventrally; rachis 0.6-4.5(-5) cm; gland 1 sessile between proximal pair (0.4-)0.6-1 mm, in profile obliquely ovate, semiovate or incurved-lanceolate, acute or acuminulate, glabrous (much eaten and then apparently 0); lfts 3-13 pairs not or scarcely accrescent upward, ascending from rachis face upward on wrinkled pulvinule 0.2-0.4(-0.5) mm, in outline obovate, oblong-obovate or broadly elliptic, obtuse-mucronulate or rarely subretuse, 9(- 10) x 2-4(-4.5) mm, ±1.7-2.8(-3.0) times as long as wide, asymmetrically rounded at base, the margin plane, the centric, dorsally cariniform midrib with 3-4(-5) pairs of camptodrome secondary and rare or random connecting tertiary venules all immersed above, the secondary venation faintly or decisively prominulous beneath; spur-lvs similar but mostly shorter, composed of fewer and slightly smaller lfts.

    Peduncles (4-)6-21 mm; racemes 1-3-fld, the axis 0-1(-2) mm; bracts oblanceolate concave, cucullate at tip, 1.7-2.4 mm, caducous; pedicels (9-)10-19 mm, commonly but not always subtended by stipitate glands; buds globose, glabrate above the base; sepals greenish with petaloid margins, strongly graduated, all obovate-suborbicular obtuse, the largest inner one 5-7 mm; petals yellow, either glabrous or thinly puberulent dorsally, not strongly heteromorphic, the 3 adaxial slightly smaller, obovate-oblanceolate, the 2 abaxial similar but one more oblique and more shortly clawed, this (12-) 13-22(-26) mm; androecium glabrous, the filaments of 4 median anthers free, 0.9-2 mm, those of 3 abaxial ones 1.8-3.5 mm, the anthers of 4 median stamens including very short, slightly oblique beak 3-5 mm, this opening by U-shaped slit, the body of 3 abaxial ones lunately incurved 3-4.6 mm, contracted into a slightly porrect tubular 1-porulose beak 0.7-1.2 mm; ovary either glabrous or densely strigulose-pilosulous; style 1-1.8 mm, 0.2-0.35 mm diam at apex; ovules (18-)20-46.

    Pod spreading or pendulous, the stipe 5-7.5 mm, the linear compressed, commonly decurved or irregularly or undulately contorted body (4.5-)6-14 x 0.6-0.9(-l) cm, the thin, finally papery nigrescent sublustrous valves low-mounded over the seeds, faintly and delicately transverse-venulose, when dry easily broken across through the interseminal septa; seeds oblong- or obovate-paddle- shaped, 2.7-3.7 x 2-2.5 mm, the testa chocolate- or chestnut-brown, scarcely lustrous, crackled, the elliptic or oblong-elliptic areole 1-1.5 x 0.4-0.6 mm.

    An ornamental senna, notable in ser. Rostratae for the arrangement of the 1-3- flowered racemes among fascicles of diminished leaves borne close together along stiff wandlike branchlets, these being long shoots produced during rainy periods whereas the fascicles are drought-adapted brachyblasts arising from axils of the primary leaves. While S. polyphylla usually has a marked individual facies it is only precariously distinct from S. pallida sens. lat. A quite similar differentiation of the branchlets occurs in some populations of S. pallida on the seasonally arid limestones of Yucatan as also in some winter-flowering, drought-deciduous S. pallida in northwestern Mexico. Here, however, the primary leaves when grown out become much larger and coarser, while the asymmetry of one abaxial petal (the cucullus) becomes more emphatic and the beak of the four median stamens is infraterminal rather than obliquely terminal. Although the origin of S. polyphylla by reduction and xeromorphic adaptation from the stock of C. pallida seems certain, the species is now abruptly and easily distinguished from Antillian forms of the latter by its small leaves, small plane leaflets and the peculiar architecture of the inflorescence.

    Revision of the material that has passed in recent times as Cassia polyphylla reveals that xeromorphic diminution of the foliage has not stopped with the typical phase of the species, now thought to be endemic to southern Puerto Rico and the United States Virgin Islands, but has proceeded to further stages in distantly disjunct populations localized on northern Hispaniola and the island of Anegada, described below as new varieties. In using the varietal key, care must be taken to distinguish the genuine primary leaves that subtend each brachyblast but are caducous (and absent from many fruiting specimens) from the smaller, more persisent leaves associated with the flowers.

    Key to the Varieties of S. polyphylla

    1. Lfts of primary lvs 5-13 pairs, of some spur-lvs at least 4 pairs; Puerto Rico, Virgin Is., Hispaniola.2. Primary lvs 2.5-5.5(-6) cm, the lfts (6-)7-13 pairs; ovary canescently strigulose-pilosulous; Puerto Rico and Virgin Is.

    169a. var. polyphylla (p. 519).

    2. Primary lvs 1.5-2.5 cm, the lfts 5-7(-8) pairs; ovary glabrous or transiently puberulent along the sutures; n.-w. Dominican Republic.

    169b. var. montis-christi (p. 519).

    1. Lfts of primary lvs 3-4 pairs, of spur-lvs mostly 2 pairs. Ovary glabrous. Anegada I.

    169c. var. neglecta (p. 520).