Senna subtrijuga

Title

Senna subtrijuga

Authors

Howard S. Irwin, Rupert C. Barneby

Scientific Name

Senna subtrijuga H.S.Irwin & Barneby

Description

19.  Senna subtrijuga Irwin & Barneby, sp. nov., foliolis symmetrice obovato- ellipticis basi utrinque cuneatis dorso glabris S. acutisepalam simulans, sed ab ea sepalis oblongo-ovatis obtusissimis ideoque alabastris globosis (nec ovoideis acutis), glandulisque petiolaribus inter amba (nec proximali solo) foliolorum paria cito separanda.—BRAZIL. Bahia: mata costeira, Santa Cruz Cabralia, 8.II. 1967 (fl), R. P. Belem & R. S. Pinheiro 3312.— Holotypus, CEPEC; isotypi, NY (2 sheets).

Vines to 10 m, the young branchlets, pulvinules and axes of inflorescence sub- appressed-pilosulous with weakly incurved or subsinuous hairs up to 0.2-0.3 mm, the smooth glabrate mature branches obscurely angulate, the thinly chartaceous lustrously olivaceous concolorous foliage glabrous or almost so, the small terminal corymbose panicle of racemes leafy-bracteate, not exserted.

Stipules erect narrowly lance-setiform 5-7 mm, at base 0.6-0.9 mm wide, early dry and deciduous before the lf.

Lvs 8-17.5 cm; petiole including cylindric pulvinus ± 2-4 cm, at middle 1-1.4 mm diam, trigonous, keeled dorsally, coarsely green-margined ventrally, the sulcus a shallow open gutter; rachis of 4-foliolate lvs 1.5-2.5 cm, a little shorter than petiole, that of 6-foliolate lvs up to 5 cm; pulvinules narrowly flask-shaped wrinkled 2-3 mm; glands sessile between each pair of lfts, plumply or narrowly ovoid, 1.6-2.3 mm tall; distal pair of lfts ascending from petiole, symmetrically elliptic- obovate, abruptly short-acuminate (4.5-)6.5-9 x 2-4 cm, a little over twice as long as wide, at apex obtuse mucronulate, at base symmetrically cuneate, the margins strongly revolute, the stout pallid tapering midrib cariniform beneath, impressed above, giving rise on each side to 9-12 major camptodrome with or without intercalary secondary veins, these with the tertiary connecting and reticular venules subequally prominulous on both faces, the ultimate defined reticulum irregular, the areoles > and <1 mm diam.

Peduncles with raceme axis 3-5 cm; racemes ±7-10-fld; bracts papery yellowish elliptic-cymbiform 3.5-5 mm, thinly puberulent dorsally ciliolate, deciduous at anthesis; pedicels 16-23 mm; buds globose glabrous; sepals scarcely graduated, broadly ovate or oblong-ovate obtuse 9.5-11 mm, all yellowish, the outer firm with membranous margins, the inner subpetaloid; petals yellow, pubescent dorsally, especially along the prominent veins, the blades oblong-obovate beyond the short claw, 2-2.2 cm; filaments puberulent, of 3 abaxial stamens 2.5-4.3 mm, of 4 median ones 1.5-2 mm; thecae glabrous, of 4 median stamens 6-7.6 mm, with short divaricate-ascending beak 0.5-0.7 mm, of 3 abaxial ones 6-7 mm with porrectly ascending beak 1.1-1.6 mm; ovary densely silky-pilosulous; style ±2.5 mm, thinly strigulose, at apex incurved but little swollen, ±0.8 mm diam; ovules ±92.

Pod and seed unknown.—Collection: 1.

Littoral forest, known only from the type-locality near Sta. Cruz Cabralia, near 16°20'S on the coast of s.-e. Bahia.—Fl. II.

Senna subtrijuga is perhaps most nearly related to S. acutisepala, which is similar in the symmetric outline of the leaflets but different in the lanceolate acute (not broadly obtuse) sepals and consequently in the ovoid acute (not globose) flower buds. The leafstalk of S. acutisepala bears only one gland, between the lower pair of leaflets, whereas that of S. subtrijuga bears a gland also between the distal pair. No other Bacillaris of eastern Brazil resembles S. subtrijuga at all closely. The epithet refers to an occasional, possibly freakish 6-foliolate leaf present on branchlets of the type-collection, the only instance that we have come across in ser. Bacillares of leaves with more than four leaflets. Until the pod of S. subtrijuga is discovered there will be some margin of doubt as to the true affinity of the species, but the morphology of the flower and the high number of ovules are characteristic of ser. Bacillares.