Senna aurantia (Ruiz & Pav. ex G.Don) 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 1: 1-454.
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Family
Caesalpiniaceae
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Scientific Name
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Type
Holotypus, BM! = NY Neg. 165; isotypi, FI, MA (hb. Pavon. 14/15), P!
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Synonyms
Cassia aurantia Ruiz ex Pav. & G.Don, Cassia dombeyana Vogel, Cassia comosa (E.Mey.) Vogel, Senna barnebyana Lass.
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Description
Species Description - Low diffuse shrubs sometimes wider than tall, except for glabrous or glabrescent upper face of lfts and dorsally glabrous inner sepals pilosulous throughout with simply incurved or subsinuous hairs ±0.3-0.6 mm, the foliage strongly bicolored, dull olivaceous above, pallid and densely pilosulous beneath, the racemes axillary to distal lvs and shortly exserted. Stipules spreading-ascending or subreflexed linear-attenuate, marginally revolute 2-5 x 0.35—0.7 mm, caducous. Lvs (ignoring some small distal ones) 6-13 cm; petiole including pulvinus 10-22 mm; rachis 3-7 cm; gland between proximal pair of lfts stipitate, in profile including the puberulent stipe 1-2 mm, the lance-ellipsoid body 0.25-0.6 mm diam; pulvinules 1-1.5 mm; lfts (4-)5-7 pairs, a little accrescent distally, oblong or oblong-obovate obtuse, minutely mucronulate, the distal pair 2-A.6 x 0.6-1.9 cm, 2.3-3.3 times as long as wide, at base inequilaterally rounded or proximally cordate and distally cuneate, the straight midrib with 6-9 pairs of slender camptodrome secondary veins immersed or faintly prominulous above, prominulous beneath, subsequent venation fully immersed or obscure. Racemes (8-) 15-35-fld, the expanded fls raised almost to level of nodding buds, the peduncle and ± elongating axis together 7-16 cm; bracts narrowly lanceolate 2.5-5 x 0.5-0.9 mm caducous; pedicels 16-27 mm; fl-buds globose when young and thinly pilosulous, the outer sepals firm 3-4 mm, the early emerging inner ones obovate-suborbicular glabrous ciliolate subpetaloid 6-8 mm; corolla zygomorphic, the glabrous petals yellow or orange-yellow drying ochroleucous dark- veined, the longest 10-12 mm; androecium glabrous, the trapezoid blade of staminodes ±2 x 1.2 mm, the filaments of 4 median stamens ±1.5 mm, of 2 latero-abaxial ones 4-5 mm, of the centric abaxial one 2.5-3 mm, the anthers of 4 median stamens 3-3.5 mm, of 2 long abaxial ones 5-6 x 1-1.3 mm, of the centric abaxial one 4-4.5 x ±0.8 mm, the 7 fertile anthers obscurely strangulated 0.3-0.5 mm below obliquely truncate apex, the biporose orifice divided by a slender septum; ovary pilosulous; style 2-3 x ±0.2 mm, not or scarcely thickened upward, the minute stigmatic orifice introrsely terminal; ovules 33-50. Pod (little known) ±5-6.5 x 0.6-0.7 cm, the body subterete, the seeds (not seen fully ripe) 2-seriate exareolate.—Collections: 9.
Distribution and Ecology - Stony hillsides and streambeds, 2000-3300 m, locally plentiful on the sources of rios Huallaga and Perene in s. Huanuco (prov. Huanuco, Ambo) and n.-w. Junin (prov. Junin, Tarma) in centr. Andean Peru.—Fl. I-IV.
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Discussion
While we provisionally maintain S. aurantia as a discrete species we find that its claim to specific status is precarious. At anthesis and even in fruit it closely simulates the form of S. pendula var. praeandina that has been collected several times at 1800 m and lower in the Palca-Chanchamayo valley in northern Junin. This differs technically in having numerous petiolar glands, longer filaments and style, more numerous ovules and truly plane-margined leaflets, but the overall resemblance is disturbing and suggests that S. aurantia may be in reality a high- altitude variant of S. pendula. It appears related also to the north Peruvian S. lasseigniana, which is similar in the re volute leaflet-margin, but is quite different in the compressed pod and fewer, uniseriate seeds. The existence on the Hualla- ga-Perene divide, within the same elevational limits and, so far as known, in the same habitats as S. aurantia, of the grossly similar S. (Stipulaceae) birostris var. huancavensis introduces the possibility of hybridization between it and outlying populations of S. pendula var. praeandina, which could conceivably have generated S. aurantia or its ancestors. Field observation of these sennas is required. Senna aurantia was cultivated in early XIX century in the Madrid Botanical Garden under the name "Cassia prostrata" and a garden specimen, probably of this stock, was sent to DeCandolle by Lagasca as "C. procumbens" (G). There are two collections of S. aurantia in the Pavon Herbarium (MA) numbered 14/15 and 14/23 ("Cassia hirsuta. Huanuco") and it was from one of these that the typus of Cassia dombeyana must have been acquired by Humboldt and that of C. aurantia G. Don by Lambert. A collection specifically attributed to Dombey (P) is an abnormal form in which inhibited sterile branchlets consisting mostly of stipules are found in most leaf-axils, giving rise to the unpublished epithet comosa. In modern times Britton & Rose described in manuscript (NY) from Macbride 3559 and 3994 a supposedly new species dedicated to the collector, and Macbride 3194 from Ambo has recently furnished the type of S. barneby ana. We regard all of these Macbride collections as representing S. aurantia, which has obviously been and even now remains a challenging puzzle to taxonomists.
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Distribution
Huánuco Peru South America| Junín Peru South America|