Senna unijuga (Rose) H.S.Irwin & Barneby
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Authors
Howard S. Irwin, Rupert C. Barneby
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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 2: 455-918.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Holotypus, US! isotypi, GH, MEXU, MO, NY, US!-Palmerocassia unijuga (Rose) Britton ex Britton & Rose, N. Amer. Fl. 23(4): 254. 1930.
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Synonyms
Cassia unijuga Rose, Palmerocassia unijuga (Rose) Britton
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Description
Species Description - Stiffly branched but not or scarcely thorny, often gnarled and crooked micro- phyllous shrubs and treelets at anthesis (0.3-)0.5-3 m, with gray or fuscous terete, ultimately lenticellate trunks and branches, the hornotinous stems, lvs, and inflorescence up to the glabrate interior sepals densely pilosulous with erect or ascending, mostly straight hairs up to 0.4-1 mm, the short bifoliolate lvs homomorphic, all solitary on long-shoots or a few fasciculate on axillary brachyblasts but these scarcely smaller, the racemes of few, proportionately large fls lateral to long-shoots, irregularly paniculate. Stipules erect linear-attenuate or setiform, often livid, those of primary lvs mostly 2-4.5(-6) mm, tardily deciduous, those of brachyblasts shorter persistent. Lvs 8-15 mm; petiole including little differentiated pulvinus 1-4.5(-5.5) mm, at middle 0.3-0.5 mm diam, obscurely depressed-sulcate ventrally; gland 0; pulvinules 0.4-0.6 mm; lfts 1 pair, broadly flabellate-obovate or obcordate, emarginate mucronulate or subtruncate acuminulate, 5-12 x 5-11 mm, 0.8-1.3 times as long as wide, at base broadly rounded or cordate on proximal and more narrowly so on distal side, the margin strongly revolute, the upper face veinless, the midrib always and often 3-5 pairs of weak, widely ascending secondary veins prominulous beneath. Racemes subumbellately 1-3-fld, the very short axis together with peduncle (4-)8-27 mm; bracts submembranous purplish or livid, lance- or elliptic-acuminate 4-5.5 x 1.2-2 mm deciduous; pedicels (7-) 10-15 mm; young fl-buds globose pilosulous, the glabrate inner sepals early emergent; sepals firm livid except for pallid margins, well graduated, the smallest outer one elliptic obtuse 4.5-6 mm, the broadly obovate-suborbicular innermost one 7.5-9 x 5.5-7 mm; petals glabrous yellow fading brownish-yellow dark-veined, 4 subhomomorphic except for size, oblong-obovate beyond the claw, one abaxial thick-clawed and heteromorphic, its blade turned at ±90° to claw, the longest petal (fully expanded) 18-26 mm; androecium glabrous, the staminodes 1.1-1.4 mm wide, the 7 fertile stamens only a little differentiated, the anthers all oblong from bluntly sagittate base a little incurved and ±1.4-2 mm diam, somewhat dorsoventrally compressed, the filaments of 4 median stamens 1.2-1.5 mm, of 2 latero-abaxial ones 1.5-2.5 mm, of the centric abaxial one 3-4.5 mm, the beaks of 4 median anthers latero-terminal very short, those of 3 abaxial more porrect but only 0.5-0.6 mm, all dehiscent by short slits; ovary glabrous; style (sometimes indistinctly demarcated from ovary) ±1.2-1.5 mm, gently incurved, 0.25-0.5 mm diam just below the terminal minute stigmatic cavity; ovules ±20-24. Pod (little known) ascending, the stipe 6-9 mm, the piano-compressed straight or slightly decurved body ±9-13 x 0.6 cm, bicarinate by the broad sutures, the stiffly papery, brown or atropurpureous glossy, faintly venulose valves scarcely raised over the seeds, their thickened margins in age cracking transversely the whole length of the pod, the seed-locules ±4.5 mm long; seeds (poorly known) compressed parallel to the valves, obtusely rhombic in outline, ±4.3 x 3.1 mm, the dull purplish-castaneous testa minutely pebbled, the lustrous elliptic areole ±1 x 0.4 mm.-Collections: 13.
Distribution and Ecology - Thorn-forest and thin oak woodland, on calcareous, gypseous and metamorphic bedrock, 1300-2000 m, narrowly localized in the Tehuacan Desert in s.-e. Puebla and closely adjoining n.-w. Oaxaca, Mexico.-Fl. VI-X(-XI).
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Discussion
A very distinct species, readily recognized by its villous-pilosulous stems and foliage, small bifoliolate leaves, broadly flabellate-obcordate, marginally revolute leaflets, and large asymmetric corolla. The transverse cracks that appear along the thickened margins of the ripe pod-valves recall S. atomaria.
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Distribution
Puebla Mexico North America| Oaxaca Mexico North America|