Monographs Details: Cassia midas 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:Caesalpiniaceae
Discussion:

11bis. Cassia (ser. Tetrapleurae) midas Irwin & Barneby, sp. nov., racemis ramulo hornotino terminalibus, bracteis bracteolisque peracta anthesi persis- tentibus, staminumque ante petala sitorum antheris erectis cum ser. Tetrapleuris, ulterius floribus parvulis (petalis 10-14 mm longis) toto- que inflorescentiae adspectu cum C. ferruginea (Schrad.) Schrad. ex DC. omnino congrua, ab hac stipulis foliaceis late sagittatis, foliolis 3-8 (nec 10-23)-jugis magnis ovato-acuminatis 3.5-11.5 (nec oblongis obtusis 2-4.5) cm longis, petalis ex albo aureo-flavescentibus, ovul- isque minus numerosis 62-84 (nec 108-156) diversissima.—BRAZIL. Estado do Acre: along road to Brasileia 12 km (s.-w.) from Rio Branco, 2.X. 1980 (fl), S. R. Lowrie, B. Lowy & V. M. de Souza 320.—Holotypus (2 sheets), NY; isotypi, A-GH, ILL, K, MICH, MO, PH, US.

Trees 10 m tall, the branchlets, leafstalks and axes of inflorescence densely minutely puberulent with incurved yellowish hairs ± 0.1-0.2 mm, the ample lvs glossy and glabrous above, olivaceous dull beneath, the showy racemes pendulous from the tip of leafy hornotinous branchlets or rarely emergent from leafless twigs of second year.

Stipules foliaceous persistent into full expansion of lf, then deciduous, in outline semi-ovate acuminate, sagittately produced backward against the stem, the blades 1-2 cm measured between tips of longer ascending and shorter descending lobe, at point of attachment up to 1 cm wide, flabellately many-nerved and sharply reticulate-venulose.

Lvs 1.5-3.5 dm, the lf-stalk rounded dorsally, shallowly openly sulcate ventrally, its interfoliolar segments ± 2-3.5 cm; pulvinules 2.5-4 mm; lfts 3-8 pairs opposite or commonly alternate along rachis, accrescent distally, ovate- or very broadly lance-acuminate 3.5-11.5 x 2-A cm, at base subsymmetrically rounded or broadly cuneate, the straight costa canaliculate on upper face, cariniform beneath, giving rise on both sides, at intervals of ± 3-6 mm, to slender, widely incurved-ascending secondary nerves, these and subsequent reticulate venules prominulous on both faces but more sharply defined above than beneath.

Racemes mostly terminal to annotinous branchlets subsessile, the pendulous axis 1-2 dm, the ± 50-80 fls expanding in rapid succession, the distal ones opening when the proximal ones have shed their androecium but not their perianth, the fls together forming a loose cylindric cluster ± 7 cm diam; bracts and bracteoles persistent into full anthesis, deciduous thereafter, all narrowly lance-acuminate, the former 3-6 mm, the latter shorter; pedicels refracted at wide angles and so twisted as to bring the vexillar petal of the resupinate corolla uppermost, at anthesis ± 2-2.5 cm; hypanthium slenderly vase-shaped ± 3 mm solid; sepals firm brownish-olivaceous obovate concave 7-8 x 4.5-6 mm, subequilong but the outermost a trifle shorter than the inner; petals opening white, turning golden- yellow at full anthesis and, following fall of androecium, orange-brown marcescent, widely equably spreading-incurved to form a shallow bowl, all elliptic widest slightly beyond middle, cuneate (not clawed) at base, obtuse at apex, 10-14 x 5.5-7 mm, the vexillar one slightly shorter and the 2 abaxial ones slightly wider than the rest; 3 antesepalous sigmoid filaments 16-18 mm, slightly dilated but not nodular distally, their obcordate anther glabrous muticous 2-2.2 x 1.6 mm dehiscent by introrse slits, 2 (dorsal) antesepalous filaments subfiliform 6-9 mm, their sterile anther 0.7-1 mm diam, 5 antepetalous filaments all erect and parallel 5-8 mm, their broadly elliptic, basally porose anther 2.6-3 x 1.7 mm; ovary densely puberulent, grooved lengthwise along each suture and along middle of each valve; ovules 62-84.

Pod unknown.—Collection: 1.

Disturbed lowland forest, known only from the headwaters of Rio Purus in s.-e. Acre, Brazil, to be sought in neighboring Peru and Bolivia.—Fl. IX-X.—Fig. 8bis.

The discovery in the neotropics of undescribed species of Senna or Chamaecrista is commonplace and expectable, but that of a new true Cassia is a rare and surprising event. While the pod of C. midas is still unknown, the general morphology of the inflorescence and that of the individual flower are so fully consonant with the small ser. Tetrapleurae as to leave no room for doubt about affinities. Within this group C. midas is instantly distinguished by the relatively few large ovate-acuminate leaflets which in outline, texture, venation and coloring resemble those of C. fistula on a small scale. In its simplified but reciprocally amplified leaves C. midas occupies in ser. Tetrapleurae the place filled in partly sympatric ser. Amazonicae by C. spruceana and C. swartzioides. In its relatively small and shortly pedicelled flowers C. midas resembles allopatric C. ferruginea much more closely than C. fastuosa var. calva, which Lowrie and his associates collected in the same place and on the same day. Cassia (ser. Amazonicae) swartzioides var. scarlatina, known to occur in the Mamore-Beni basin both in Bolivia bordering on Acre and in adjoining Rondonia, is comparable to C. midas in foliage, but differs fundamentally in the stiffly ascending raceme-axis, clawed and appendaged vexillum, and resupinate antepetalous anthers. The possibility that C. midas is a hybrid between C. fastuosa and C. swartzioides var. scarlatina has been considered but rejected on the grounds that its inflorescence and floral architecture show no influence whatever of ser. Amazonicae and that a hybrid hypothesis is superfluous to account for one more instance in Cassia of this type of leaf modification. Pods, however, are needed to settle the question beyond dispute.

The petals of C. midas are golden-yellow in flowers dried at full anthesis and fade after the stamens are shed to bright orange-brown, but they are said by the collectors to open white and change to yellow, a pattern unknown elsewhere in Cassia. The sequence of color-change suggested the epithet.

Efforts should be made to introduce this handsome floriferous cassia into tropical gardens, where it would surely be a welcome addition to the small but distinguished company of Pink and Golden Showers already in cultivation.

Narratives:Cassia midas