Senna centranthera 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, NY; isotypi, GH, US.
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Description
Species Description - Arborescent shrubs with trunk to 3(-?) cm diam, becoming 4-5 m tall, the hornotinous branches densely clad in long multifoliolate lvs and terminating in an ample panicle of many-fld racemes, except for the glabrous upper or both faces of the dull olivaceous, either subcon- or discolorous lfts and for the dorsally glabrous sepals commonly pilosulous throughout with spreading-ascending pale hairs to 0.2-0.45 mm, sometimes glabrate except for residually puberulent lf- stalks, the panicle of racemes at least distally leafless and exserted from foliage. Stipules early reflexed, herbaceous, deltate-ovate-acuminate or broadly lanceolate 6-12 x 2.5-5(-6) mm, deciduous. Lvs 15-35 cm; petiole including little swollen but discolored pulvinus 2-3.5 cm, at middle 1-1.6 mm diam, rounded dorsally, narrowly winged and open-sulcate ventrally, the wings of lf-stalk segments slightly widened upward and the sulcus there deeper; petiolar glands 0; lfts 20-33 pairs, the proximal ones smaller but the rest not or little graduated, all ascending from rachis, face upward, on scarcely dilated pulvinule 0.7-1.3 mm, in outline lance- to narrowly ovate-oblong or lance- elliptic, obtuse mucronulate (8-)15-40 x (3-)4-12 mm, 2.7-4 times longer than wide, at strongly assymmetric base rounded on both sides or broadly cuneate distally, the slender midrib with ±8-10 pairs of major camptodrome and often some intercalary secondary veins finely prominulous on both faces, the tertiary venulation yet finer, scarcely raised. Racemes crowded along a straight primary axis 1-2.5 dm, the lower ones leafy- bracteate, at first densely then loosely 10-45-fld, the 1-2 simultaneously expanded fls standing well below the unopened buds, the axis including peduncle becoming 7-20 cm; bracts submembranous lance- or ovate-acuminate 2-4.5 mm, caducous from below young buds at first elongation of pedicel; pedicels at and after full anthesis 9-16 mm; fl-buds obovoid-ellipsoid obtuse, except for sometimes minutely ciliolate sepals glabrous; sepals submembranous, brown except where exposed in vernation, the inner ones subpetaloid, all broadly oblong-elliptic concave, finely many-nerved from base, subequal in length but the inner a little broader, the longest 9-11.5 mm; petals yellow drying stramineous brown-veined, all glabrous, little heteromorphic but varying from broadly oblanceolate to obovate-cuneate beyond the slender claw, the 3 adaxial a trifle longer than the abaxial pair, the longest 13-20 mm; androecium glabrous, functionally 2-merous, the filaments of 4 median stamens 1.8-2.5 mm, of the 3 abaxial ones 3.3-5 mm, the anthers of 4 median and the centric abaxial one sterile or greatly reduced in size, shallowly sigmoid 3-4.5 mm, with porrect beak 0.7-1.3 mm, those of the 2 large abaxial ones lunately incurved 10-14 mm, almost imperceptibly narrowed distally into an erect beak dehiscent by minute terminal, ultimately confluent slits, all anthers strongly dorsoventrally compressed, sagittate at base, the acute descending spurs of the larger anthers 1.5-2.5 mm; ovary glabrous, narrowed into a filiform incurved or hooked style 4.5-6.5 mm; ovules ±24-30. Pod obliquely pendulous, the stipe ±3 mm, the broadly linear body 7-11 x ± 1.4 cm, strongly piano-compressed and carinate by the sutures but the lustrous green, at length stiffly papery valves raised over each seed as a prominent fuscous umbo, the seed-locules ±4 mm long and twice as wide, occupying a little more than half the pod’s width; seed unknown.—Collections: 12.—Fig. 28.
Distribution and Ecology - Seasonally wet open woodland and semi-deciduous scrub thickets in hill-savanna, sometimes on pedregal and probably confined to volcanic bedrock, 1350-2000 m, local along the Pacific slope and crest of Sa. Madre del Sur in s. Jalisco (mun. Autlan), w. Michoacan (mun. Tsitsio, Quitupan, Cotija de la Paz and Coalcoman), Guerrero (mun. Tixtla and Chilpancingo), and w. Oaxaca (distr. Juxtlahuaca), Mexico.—Fl. VI-XI.
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Discussion
Senna centranthera appears to be a submontane derivative of lowland S. nicaraguensis, morphologically modified by reduction of stipules and bracts and by simultaneous doubling in number and halving in size of the leaflets. It might appear a priori that this evolutionary sequence is reversed, for foliaceous stipules and ample colored bracts must surely be advanced features in Senna as a whole. In the narrower context of ser. Pictae, however, the petaloid bracts, unless they have made independent parallel appearances in North America, South America, Africa and Australia, which seems unlikely, are antecedent to the smaller, more conventional ones found in S. centranthera and its Andean kindred described below. The range, habitat and superficial gross aspect of S. centranthera roughly coincide with those of S. (sect. Chamaesenna) multifoliolata and possibly may give rise to misidentification. The glandless leaf-stalk, the exserted panicle, and most importantly the androecium proper to sect. Senna, not to mention the cristate pod, are the fundamentally distinctive characters of S. centranthera.
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Common Names
Palo Maria
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Distribution
Jalisco Mexico North America| Michoacán Mexico North America| Guerrero Mexico North America| Oaxaca Mexico North America|