Senna arnottiana (Gillies ex Hook.) H.S.Irwin & Barneby

  • Authors

    Howard S. Irwin, Rupert C. Barneby

  • Authority

    Irwin, Howard S. & Barneby, Rupert C. 1982. The American Cassiinae. A synoptical revision of Leguminosae tribe Cassieae subtrib Cassiinae in the New World. Mem. New York Bot. Gard. 35, part 1: 1-454.

  • Family


  • Scientific Name

    Senna arnottiana (Gillies ex Hook.) H.S.Irwin & Barneby

  • Type

    Lectoholotypus (Gillies, fr) and paratypus (Macrae, fl), mounted on one sheet, K (hb. Hook.)! = NY Neg. 1568; isotypus (Gillies), FI!

  • Synonyms

    Cassia arnottiana Gillies, Cassia andina Phil., Cassia arnottiana var. andina (Phil.) Reiche, Cassia lorentzii Niederl.

  • Description

    Species Description - Low several-stemmed shrubs of bushy outline 1.5-8 dm, with leafless trunks at first brown smooth corpulent, then gray or grayish-brown and toughly woody, up to ±1 cm diam, permanently angulate by prominent, dorsally blunt-keeled lf-spurs distally wider than the associated lf-stalk, the densely leafy young stems, lf-stalks and axes of inflorescence minutely pilosulous or remotely puberulent with fine spreading, incumbent or curly white hairs up to 0.15-0.3 mm, the firmly chartaceous or subsucculent foliage olivaceous or glaucescent, often yellowing in age, the subconcolorous lfts glabrous or remotely ciliolate only along midrib beneath, the leafy-bracteate few-fld racemes subterminal, shortly exserted. Stipules erect herbaceous linear-lanceolate or -subulate 2-5 x 0.4-0.9 mm, tardily deciduous. Lvs (1.3-)2-5 cm; petiole including wrinkled pulvinus (1.5-)2.5- 10(-13) mm, at middle 0.7-1.2 mm diam, when dry carinate dorsally, the ventral sulcus narrow shallow; rachis (5-)9-32 mm; gland between proximal pair (rarely also between second pair, or only one and this displaced to rachis between proximal and second pairs), shortly or subobsoletely stipitate, in profile 0.6-1.7 mm tall, the erect or incurved, slenderly ovoid acute or subulate head 0.15-0.5 mm diam, the whole gland not seldom degenerate, spiculiform or even 0; pulvinules variably dilated, usually yellowish and wrinkled when dry, 0.4-0.9(-1.2) mm; lfts commonly 3-6, locally (in Chile) up to 6-8 pairs, little or not graduated along the rachis, mostly broadly obovate obtuse or emarginate (obscurely deltate-acuminulate) or less often oblong-elliptic obtuse up to 7-14 mm, at scarcely or slightly oblique base either rounded or cuneate, the margin plane, the venation (both between plants and between lvs of one plant), variable, of thick-textured lfts fully immersed except for the midrib dorsally, of thinner (or immature) ones the midrib giving rise to 2-4 pairs of camptodrome (and rarely 1-2 faint intercalary) secondary veins raised ± sharply on dorsal but at best faintly so on ventral face, a tertiary venulation rarely incipient, then weak and irregular. Racemes loosely 2-5-fld, the first open fls raised to or beyond level of nodding buds, the axis together with peduncle becoming 2.5-5.5 cm; bracts submembranous elliptic obtuse cymbiform 2.5-5 mm, usually persistent into early anthesis, then deciduous; mature pedicels 12-25(-31) mm; fl-buds subglobose, usually puberulent at base, glabrous distally; sepals subpetaloid, yellowish or brownish, delicately several-nerved from base, not much graduated, all obovate or broadly oblong-oblanceolate obtuse, the longest 7-10 mm; petals orange-yellow, when dried brown-veined but not whitening, of subequal length, the 3 abaxial ones broadly obovate-flabellate obtuse or shallowly emarginate, the 2 abaxial narrower, elliptic-obovate or -oblanceolate, nidulating the long stamens, the longest petal 12-14.5 mm; androecium glabrous, the staminodes obovate or obcordate 1.1-1.5 mm wide; filaments of 4 median stamens 2-2.8 mm, of 2 longest abaxial ones 4-8.5 mm, of the centric abaxial one 2.5-7.5 mm, the anthers of 4 median stamens 3.6-4.3 mm, of the long pair of abaxial ones 5-5.5 x 1.1-1.3 mm, of the centric abaxial one 4-4.6 x 1-1.3 mm, all anthers obliquely truncate at apex and dehiscent by 2 short slits separated by a shallow notch; ovary either glabrous or puberulent; style linear-subulate, evenly incurved 0.9-1.6(-1.8) x 0.2-0.3 mm, the minute stigmatic cavity terminal; ovules (5-)6-14. Pod obliquely spreading-declined from ascending pedicel, its stout stipe 2-3 mm, its body narrowly oblong, straight or decurved, often variably and randomly distorted or strangulated where ovules abort, (2.5-)3.5-7 x 1.1-1.6 cm, laterally compressed but turgidly mounded over the expanded ovules, bicarinate by the sutures, the thin-textured valves becoming brown and papery, pallid or yellowish along the sutures, delicately cross-nerved, the membranous interseminal septa well-developed, the seed-locules broader than long; seeds vertical to the pod’s long axis but turned edgewise to the valves and presenting their broad faces to the septa, plumply compressed-obovoid or oblong-obovoid 6-8.5 x 3.8-7 mm, the dull chocolate-brown testa smooth, the areole broadly elliptic-obovate 4-5.2 x 3-4 mm.—Collections: 20.

    Distribution and Ecology - Dry stony hills and talus slopes of rocky quebradas, ascending from the e. foothills of the Andes at (800-)900-2500(-2800) m along and w. of the crest, locally plentiful along the main Cordillera, in Argentina from Mendoza s. through Neuquen to s.-w. Rio Negro (lat. 33°-41°25'S) and in Chile from e. margin of Coquimbo (dept. Illapel) s. to Bio Bio (lat. 31°40'-37°30'S).—Fl. X-XII.

  • Discussion

    This is an easily recognized senna, the generally xeromorphic habit, the sturdy leafless old stems angulately ribbed by proportionately exaggerated leaf-spurs, the thick-textured, at first glaucescent but later yellowish foliage and the coarse turgid pods all contributing to a peculiar facies. It is somewhat variable in number and venulation of the leaflets. On the Argentine slope of the Andes, where the species ranges from the foothills to the high valleys near the watershed, the leaflets are consistently few, in larger leaves 4-6 pairs, and lack externally visible venulation other than the dorsally prominulous midrib. On the Chilean slope, where S. arnottiana is not recorded from below 2000 m, the leaflets vary from veinless to sharply penniveined dorsally and rise in some populations to 6-8 pairs. With increase in number the leaflets dwindle in size and tend to shrink from broadly obovate-obcordate to oblong-elliptic. From the protologue it appears that C. andina was based on specimens in which visible venulation coincided with 8 pairs, but we now know that number and prominence of the veins are not correlated and that relatively numerous leaflets are not geographically segregated. In consequence we follow Bentham, Burkart, and annotations by Sandwith at Kew, in accepting C. andina as a synonym of S. arnottiana. Cassia arnottiana var. sericea Burkart ex Bravo, Darwiniana 23(1): 266, fig. H. 1981, based on R. Martinez Crovetto 32 (SI, not seen) from the department of Huiliches, Neuquen, appears to be an individual variant with densely pubescent branchlets.

  • Common Names

    sen, tara, trapela guen

  • Distribution

    Mendoza Argentina South America| Neuquén Argentina South America| Rio Negro Argentina South America| Coquimbo Chile South America| Bío-Bío Chile South America|