Howard S. Irwin, Rupert C. Barneby
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.
Caesalpiniaceae
Species Description - Trees 6-20 m, potentially flowering as juvenile shrubs, when adult with rounded crown and trunk up to 6 dm diam, the glabrescent gray-brown, atro-castaneous or livid annotinous branchlets angulately ribbed, the hornotinous ones together with lf-stalks, lfts (except rarely the upper face) and axes of inflorescence varying from densely pilosulous to minutely puberulent with spreading, incumbent or rarely subappressed, commonly rufescent hairs up to 0.1-0.35 mm, the phyllotaxy spiral, the lvs bicolored, when dry dull brownish-olivaceous above, paler beneath, the long loose racemes of fragrant yellow fls terminal to current year’s, obliquely geotropic leafy branchlets or to leafless branchlets emergent laterally from annotinous branchlets ± coinciding with the new flush of foliage. Stipules thinly herbaceous 2-lobed, the ascending lobe narrowly lanceolate or lance-attenuate (1.5-)2-7 x 0.4-1 mm, the descending one similar but only l-2.5(-3.5) mm, the whole blade deciduous before the associated lf, sometimes prior to its full expansion. Lvs (10-) 12-28 cm, becoming longer and more complex upward along each branchlet; petiole including firm pulvinus 14-26 mm, at middle 0.9-2 mm diam, openly shallowly grooved ventrally; rachis (5-)8-22.5 cm, its longer interfoliolar segments (6-)8-14 mm; pulvinules (1-) 1.2-2 mm; lfts (7-) 10-21 (-23) pairs, opposite or less often scattered, a little decrescent toward each end of rachis, the largest adult ones narrowly oblong or oblong obtuse mucronulate or apiculate 22-45(-48) x 6.5-12(-15) mm, (2.6-)2.9-4.1(-4.3) times as long as wide, at base inequilaterally cuneate, rounded, subtruncate or proximally subcordate, the broader distal side commonly abruptly obtusangulate, the mature margin revolute, the midrib depressed above, cariniform beneath, the 6-9(-10) pairs of camptodrome with few random intercalary secondary veins finely prominulous on both faces, a weak open tertiary venulation scarcely raised or immersed. Racemes sessile or almost so, loosely 20-65-fld, the tapering, geotropically arcuate (but not pliantly pendulous) axis elongating prior to anthesis and many (or all) fls usually expanding subsimultaneously, the mature axis (6-) 12-30(-36) cm; bracts firm, lance-ovate or lance-acuminate to -caudate 3-10 x 1.6-2.2 mm, persistent with the pair of similar but shorter, proportionately broader bracteoles into or shortly past anthesis, then deciduous; pedicels widely divaricate or from pendent axis refracted and twisted so as to restore its fl to vertical, including the slenderly vase-shaped hypanthium (21 -)25-45 mm, the hypanthium itself (1.5-)2-4 mm; fl-buds ellipsoid obtuse, densely finely puberulent, the firm ovate- obovate sepals only a little graduated, the longest inner one 6.5-11 (- 12) mm, all reflexed at full anthesis and deciduous promptly thereafter; petals yellow sometimes brick-red in age, often puberulent dorsally along veins, widely expanding and almost plane at full anthesis, elliptic or obovate subhomomorphic (9-) 11-28 x 5-15 mm, at base either abruptly cuneate or when broad contracted into a claw up to 1 mm long; androecium glabrous except for dorsally pilosulous anthers of 3 long stamens, the sigmoid filaments of these dilated distally (ribbon-like) and (measured along curvature) 18-46 mm, the other 7 filaments straight erect ± dilated proximally and tapering distally, variably diminished backward toward the vexillum, the 4 median antepetalous 6-17 mm, the 3 adaxial 3.5-13 mm, the 2 antesepalous hamately recurved at apex, the anthers of 3 long stamens ovate obtuse 2.3-3.5 x 1.5-1.9(-2) mm, of 4 median more narrowly obovate- hastate 2.4-3.5 x 1.1-1.8 mm, of 3 adaxial minute, sterile or nearly so, (0.5-)0.7-l .3 mm diam; ovary pilosulous, its stipe 3-5.5 mm, its style (externally scarcely differentiated) 1.5-2.7(-3) x 0.6-0.8 mm, incurved at apex and abruptly contracted into the intro-antrorse ciliolate stigmatic cavity 0.1-0.2 mm diam; ovules 108-156. Pod (little known) pendulous, slenderly rodlike 4.5-7 (acc. Mexia -8.8) dm x 1.7 cm x 1.4 cm, straight, a little laterally compressed, coarsely bluntly 2-carinate both ventrally and dorsally by greatly thickened double sutures, gently convex and obscurely corrugated laterally, the cross section oblately elliptic, the thin, early glabrate exocarp becoming skinlike, transversely cracked, livid-cas- taneous and lustrous, the woody endocarp ±0.8 mm thick and the interseminal septa only a trifle thinner, the locules ±6-7 mm long; seeds 1-seriate, turned broadside to the septa, each clothed in a pulpy envelope which contracts around it in drying as a loose coat separated from the locule-wall, in form (immature) like that of kindred spp., not seen ripe.
Like all genuine cassias C. ferruginea is a handsome, potentially long-lived tree, notable for its abundant drooping racemes of sweet-scented flowers and for its extremely long and narrow pod double keeled along both sutures. It differs from related and partly sympatric C. leptophylla, which has a similar but more massive 4-keeled pod, in the more numerous oblong and smaller, more simply penniveined rather than reticulate leaflets, and in the narrow and loose, not congested corymbiform racemes of smaller flowers borne on pedicels about 2.5-4.5 (not 6.5-8) cm long. The nodular swelling on the outer curve of the three long stamens which characterizes C. leptophylla alone among native American cassias is represented in C. ferruginea by a gradual ribbonlike dilation, and their anthers are substantially smaller, 2.3-3.5 (not 3.6-4.5) mm long. The pod of neither species is well known, but that of C. ferruginea appears on present evidence to be at once longer and narrower, its length correlated no doubt with a generally higher number (±108-156, not 80-114) of ovules. The largest-flowered forms of C. ferruginea resemble allopatric C. fastuosa in the elongating raceme of persistently bractate flowers, but can be separated infallibly at anthesis by the narrow stipules and sessile or subsessile petals and in fruit by the more coarsely 4-costate pod.
From early times the leaflets and flowers of C. ferruginea (or C. staminea) have been noticed as variable in size and its pubescence as variable in length and density, but the modes of variation were known by Bentham (1870, I.e.) to be poorly correlated, a fact confirmed by modern collections. On the other hand the accumulated material of C. ferruginea shows an emphatic clinal curve of variation in amplitude of petals and length of sigmoid stamens that corresponds with north-south dispersal. Although the curve seems continuous and there are a few equivocal collections from central Minas Gerais, the extreme forms are so strikingly different that we feel justified in recognizing two taxonomic units.