Typus: Madagascar. Province de Diego-Suarez/Antsiranana: sous-préfecture d'Ambanja, presqu'île d'Ampasindava, commune rurale d'Ampôpô, forêt de Bongomihiravavy, 13°45′54″S 48°04′21″E, 9.XII.2010, Ammann, Tahinarivony & Madiomanana MYA 170 (holo-: G!; iso-: S!, TEF).

Species haec corolla plerumque flava et coronae lobis filiformibus Calyptrantherae sulphureae similis sed differt corolla magis viridula et brunneole maculosa et lobis non nisi prope basin pubiscentibus, corona aurantiaca necnon antherae connectivo basaliter distincte piloso. A C. sulphurea et C. gautieri differt corolla viridiflava et fere glabra.

Suffrutescent twiner c. 2 m long with abundant milky latex. Branches and younger leaves densely covered by more or less straight to bent often retrorse rather stiff reddish hairs, glabrescent. Leaves opposite, coriaceous, shining green above, paler below, usually revolute at the very margin; blade 9–13 × 3–4.2 cm, elliptic to somewhat obovate, cuneate at base, acuminate at apex, with reddish bent hairs beneath, glabrescent above or sometimes with few remaining hairs especially along the midrib; margins entire; venation pinnate and looped, reticulate; midrib when dry distinctly impressed above and raised beneath; primary veins curved, diverging at 70° to 90° from the midrib; secondary veins grossly reticulate, slightly raised on both sides when dry; petiole distinct, 0.5–1.2 cm long, with dense reddish hairs. Inflorescences extra-axillary, shorter than the adjacent leaves, hairy; cyme with few or one flower at the time on a c. 8–12 mm long peduncle; pedicels c. 1.5–2 cm long; bracts and bracteols narrow, 3–4 mm long. Flowers pentamerous, actinomorphic. Calyx lobes united only at the very base, 3–4 × 1 mm, much longer than the corolla tube, narrowly triangular, acute, with long reddish hairs outside, glabrous inside. Corolla elliptic in bud, contorted with the left lobe margin overlying, not twisted, with the lobes fused at the base only into a short tube, greenish yellow with small brown dots which disappear towards the centre, and with each petal at the very base with purplish brown coalescent dots bounded by yellow ridges (corolline corona); tube c. 0.7 mm long; lobes c. 8–10 mm × 4–6 mm, elliptic, bluntly acute at apex, rotate, glabrous except for a patch of dense, white, long and wavy hairs on the inside at base. Stamens in a column inserted at the base of the corolla tube; staminal column in total c. 4.9 mm high; filaments broad with horny margins (anther wings) and with a cup-like projection below (pollinium entrance), basally coalescent into a short cylinder; anthers with connectives excluded c. 1.4 mm long; connectives much prolonged into five filiform erect appendages grouped together below in a column but free above, c. 3.5 mm long, with long hairs dorsally at base and between thecae. Corona lobes erecto-patent, filiform, slightly hook-shaped at apex, c. 2–3 mm long, glabrous, orange, shorter than the prolonged connectives. Pollinaria not seen. Style narrow and cylindric at lower half but conical below the style head; style head with a discoid lower part that abruptly narrows into the style and with an upper narrower and shortly projecting part. Fruits unknown.

Distribution and habitat. — Calyptranthera viridiflava is only known from the type locality in the Ampasindava peninsula in northwestern part of Madagascar, and found in dense humid forest at 450 m altitude. It was tangled in leafs of a Dypsis pinnatifrons Mart., 7 m off the ground. It was collected in flower in early December (Fig. 2).

Taxonomic discussion. — A striking feature of C. viridiflava is the colour of its flowers. The corollas in Calyptranthera are generally reddish, from pale rose or almost white to lavender and purple or dull brown. In contrast, C. viridiflava has together with only one more species, C. sulphurea Klack., yellow to greenish yellow flowers. Calyptranthera sulphurea, which is known from Daraina in northeastern Madagascar, is the species that shows closest affinity with C. viridiflava, not only by its colour but also by its filiform corona lobes and structure of the androecium. However, although both have basically yellow flowers the colour pattern of the flowers differs significantly. In C. viridiflava the corolla is more greenish yellow and most of the petal lobes are covered with brownish dots. In contrast, the petal lobes in C. sulphurea are mostly uniformly yellow and brownish dots are in this species confined to the base of the corolla lobes. Furthermore, in C. viridiflava both thecae and the prolonged appendages of the connectives are uniformly greenish (vs. thecae vivid brown in contrast to the clearly yellow connectival appendages in C. sulphurea), the corona lobes are orange (vs. brown), the connectives are covered by long hairs between the thecae (vs. papillate) and the petals are glabrous except for a small patch of long wavy hairs at base (vs. hairy all over inside in C. sulphurea). Finally, the staminal column of C. viridiflava is much longer than that of C. sulphurea. Calyptranthera villosa Klack., a second species from Daraina, is similar to C. viridiflava by the hairy connectives and filiform somewhat hook-shaped corona lobes. It is easily distinguished, however, by the brownish pink and villous petal lobes. Calyptranthera viridiflava is together with C. gautieri the only species of the eleven hitherto described taxa of Calyptranthera that are distributed in western Madagascar. Both were described from Sambirano phytogeographical domain at some 50 km from each other, but seem not to be very closely related and are easily distinguished by several characters. In addition to its greenish yellow flowers (in C. gautieri brownish dark red), C. viridiflava differs also by its glabrous petal lobes (vs. whole lobe hairy inside), hairy anthers (vs. glabrous) and by its filiform corona lobes (vs. spathulate in C. gautieri).