19. Cuphea rionegrensis Lourteig (1987: 38).

Type:— BRAZIL. Amazonas: Rio Negro, between Manaus and S ã o Gabriel, Temendui lagoon, campina, 00º35’S, 64º40’W, 29–30 June 1979, Poole 1790 (holotype P [01901841] image!, isotypes INPA!, NY image!). Fig. 15H–M, 18.

Subshrubs 50–100 cm tall; stems erect, indumentum strigose, one-armed trichomes, mixed with glandular trichomes ca. 0.7 mm long, and eglandular trichomes with curved apices, sometimes the indumentum is distributed in a longitudinal band along the stem; internodes 0.7–2.5 cm long; brachyblasts absent. Leaves opposite, membranaceous, petioles ca. 1 mm long, blades 10–30 × 1–2 mm, linear to narrow-oblong, apex acute, base acute to obtuse, margin plane, sparce glandular trichomes on both surfaces, one-armed appressed trichomes on the main vein of the abaxial surface and sometimes on the adaxial surface; hyphodromous, secondary veins rarely visible. Racemes 9–15 cm long, frondose, compound, elongated, indistinct; bracts similar to leaves, subequal pairs. Flowers alternate, pedicels 1.5–3 mm long; bracteoles 0.3–0.4 mm long, ovate; floral tubes 5–7 mm long; spur obtuse, deflexed; outer surface green, indumentum glandular and slightly pubescent, one-armed appressed trichomes on the distal portion; inner surface villous behind the stamens, densely pilose on the rest of the floral tube; petals 6, pink to purple, subequal, two dorsal 3.3–4 × 1.3 mm, narrow-obovate, four ventral 3.3–3.8 × 1.2 mm, narrow-obovate; stamens free in the upper third of the floral tube, five antesepalous exserted, four antepetalous subexserted; pistil 4.7–5 mm long; ovary glabrous; style glabrous; ovules 2–3; nectary 0.7–1 × 0.3–0.8 mm, deflexed. Seeds 2–3, 1.9–2 × 1.6–1.7 mm, broad-elliptic, apex obtuse, base obtuse, margin obtuse.

Phenology: —Collected with flowers in June, September, and October, and with fruits in June and September.

Distribution and habitat: — Brazil, in Amazonas state (Fig. 18); in white sandy “campinas”, on the banks of the Negro river; ca. 50 m elev.

Conservation status: — Cuphea rionegrensis was categorized as Data Deficient (DD) due to sparse records and poor information about collection sites.

Specimens examined: — BRAZIL. Amazonas: Rio Negro, Campina de Temendaui, ca. 40 km below Tapuruquara [Santa Isabel do Rio Negro], 13 October 1978, Madison et al. 6220 (F image!, INPA!); margem esquerda do Rio Negro, entre Barcelos e Tapuruquara [Santa Isabel do Rio Negro], 13 October 1978, Nascimento 622 (MG!, NY image!, P image!); along the Rio Negro between Manaus and S ã o Gabriel, Temendaui, 00º35’00”S, 64º40’00”W, 30 June 1979, Alencar 256 (P image!); Rio Negro, lugar Temendauí, 1 dia de viagem em motor de 116 HP para chegar na cidade de Tapuruquara [Santa Isabel do Rio Negro], 31 June 1979, Maia et al. 256 (INPA!); Rio Negro, Temedauí, right river bank 2 hours below Tapuruquara [Santa Isabel do Rio Negro], 04 September 1979, Kubitzki et al. 126 (INPA!); Rio Preto, Fróes 34889 (IAN!).

Cuphea rionegrensis is characterized by linear to narrow-oblong, membranaceous, usually hyphodromous leaves (Fig. 15H, I) and slender floral tubes, 5–7 mm long. It grows in white sandy “campinas” on the banks of the Negro river, deep in the Amazon rainforest in northern Amazonas state, Brazil. Cuphea rionegrensis is a poorly known species, described from scarce herbarium material. It can be confused with C. antisyphilitica, which is distinguished by its ovate to oblong, brochidodromous leaves, and the more robust floral tubes, 7–9 mm long. Preliminary results from an ongoing robust molecular phylogeny of Cuphea confirm C. rionegrensis as a distinct species (Cavalcanti, pers. comm.).