Ceratostema oyacachiensis Luteyn, Sida 21(3): 1271, fig. 1. 2005. Type. Ecuador. Napo: Río Chalpi at confluence with Río Oyacachi, 00°15’S, 77°58’W, 2500-2550 m, 21 May 1996 (fl), B. Ståhl et al. 2512 (holotype: NY; isotypes: AAU, K n.v., MO n.v., QCA n.v., QCNE n.v.).

Epiphytic shrubs; mature stems terete or subterete and bluntly angled, glabrous, the bark grayish, cracking longitudinally and exfoliating in thin strips; twigs terete to subterete, striate, glabrous, reddish-brown; axillary buds arising up to 3. 5 mm above leaf-nodes, the outer pair of scales 2, valvate, relatively obscure, narrowly triangular, acuminate, up to 2.5 mm long. Leaves alternate, flat, the blades thick-coriaceous, lanceolate, 5.2-11 x 1.2-2.4 cm, basally broadly cuneate to obtuse, apparently decurrent onto petiole, apically long-acuminate, glabrous, the venation weakly 3-5-plinerved from near base, the midrib thickened and raised in proximal ca. 5 mm then plane to weakly impressed distally adaxially, raised and conspicuous abaxially, the lateral nerves plane to very weakly impressed adaxially and raised abaxially, the reticulate veinlets obscure adaxially and weakly raised abaxially; petioles subterete, slightly flattened adaxially, slightly winged to blade, ca. 4-11 mm long, glabrous. Inflorescences axillary, sometimes located along tips of branches where leaves have fallen, racemose, 2-8-flowered, somewhat short-pedunculate with flowers congested distally; rachis subterete, striate, 1.5-2.5 cm long, glabrous; floral bract caducous, not seen; pedicel terete, striate, 15-18 mm long, glabrous, articulate with calyx; bracteoles 2, located near base, caducous, ovate, ca. 2.2 mm long, apically long-acuminate, marginally glandular-fimbriate. Flowers 5-merous, pendent; calyx 6-9 mm long, glabrous, the tube obconic, truncate, terete to bluntly 10-ribbed, 2.5-3 mm long, the limb open, spreading to rotate, 5-6 mm long, the lobes broadly ovate, short-acuminate, 3-4 x 5 mm, with margins thin and seemingly lacerate-glandular, the sinuses acute; corolla thick-carnose, bistratose, cylindrical but slightly broadening distally, terete in cross-section, ca. 37-46 mm long, 7-9 mm basal diam. and 9-14 mm diam. at throat, orange, glabrous externally, the lobes broadly deltate, bluntly acute, 4-7 x 6-7 mm, green, densely floccose internally with flat, translucent trichomes to 2 mm long; stamens 10, ± equaling corolla in overall length, equal with each other, ca. 36-43 mm long, the filaments distinct, glabrous, ca. 4-6 mm long, the anthers ca. 33-39 mm long, the thecae ca. 9.5-11 mm long, basally conspicuously granular-papillate, the tubules ca. 24-28 mm long, seemingly connate in proximal 2/3, dehiscing by terminal pores ca. 0.2 mm diam.; style exserted, to 56 mm long, glabrous. Fruit not seen.

Distribution. Endemic to northeastern Ecuador, where it occurs in both primary and disturbed forest, at ca. 1500-2550 m.

Ceratostema oyacachiensis is characterized by having leaf blades that are basally broadly cuneate to obtuse with plinerved venation, calyces that are articulate with the pedicels, calyx tubes that are terete to 10-ribbed, calyx limbs that are inconspicuous and rotate, calyx lobes that are short and lack basal, circular glands but do possess instead lacerate-glandular margins, corollas that are large and thick-carnose, broadening slightly distally and having short and broad lobes. In Luteyn’s (1996) key to the Ecuadorean species of Ceratostema, this species is found in the vicinity of C. pedunculatum Luteyn, C. prietoi A. C. Sm., C. nubigenum (A. C. Sm.) A. C. Sm., and C. ventricosum Luteyn. It is distinct from all those species, however, based on its combination of characters mentioned above. If it were not for the articulate calyx/pedicel, this species might be placed in the genus Semiramisia due to its rotate calyx limb and corolla that broadens slightly distally with relatively short, broad lobes. Additional collections of this species are needed to determine its morphological range of variation and relationships.