1. Anthers horseshoe-shaped, 1-loculed, dehiscing transversely............................................................................................ O. flavida
- Anthers broadly oblong, 2-loculed, dehiscing longitudinally............................................................................................................ 2
2. Stamens included, floral tube thin tubular...................................................................................................................... O. jasminina
- Stamens exserted, floral tube conical or campanulate........................................................................................................................ 3
3. Corolla yellow............................................................................................................................................................. O. hainanensis
- Corolla orange-red.............................................................................................................................................................................. 4
4. Leaf blade adaxially grey pubescent, base oblique, subrounded to cordate, margin serrulate; petiole to 14.5 cm, densely pale brown villous; cymes 1–3 (or 4)-flowered; corolla 1.7–2.4 cm, tube 1.1–2 cm....................................................................... O. dasyantha
- Leaf blade adaxially grey to brown pubescent and villous, base sometimes oblique, cuneate to subcordate, margin crenate-serrate; petiole to 6 cm, densely pale brown woolly; cymes 3–8-flowered; corolla ca. 1.6 cm, tube 9–11 mm........................................................................................................................................................................................................... O. dasyantha var. ferruginosa