Oxypetalum, Brown, 1810

Farinaccio, Maria Ana & Goyder, David J., 2016, A synopsis of Oxypetalum (Apocynaceae) in Bolivia, with the description of one new species and a key to species in Bolivia, Phytotaxa 267 (1), pp. 16-28 : 16-17

Key to the 20 species of Oxypetalum in Bolivia

1. Stems erect, not twining.....................................................................................................................................................................2

- Stems twining, not erect.....................................................................................................................................................................7

2. Inflorescences terminal on long peduncles, globose; lateral inflorescences associated with few upper nodes only.........................3

- Inflorescences mostly lateral, more evenly distributed along stem....................................................................................................4

3. Corona lobes and style-head appendages barely exserted from mouth of corolla tube; inter-Andean dry valleys.............................. ...................................................................................................................................................................... Oxypetalum arnottianum

- Corona lobes and style-head appendages erect and clearly exserted beyond mouth of corolla tube; eastern lowlands...................... ............................................................................................................................................................................ Oxypetalum crispum

4. Corona lobes broadest distally with a truncate apex and a linear tooth on the inner face; stems with lanate indumentums............... ............................................................................................................................................................................. Oxypetalum erectum

- Corona lobes broadest towards the base, apex rounded to acute, entire or bifid,.without a tooth on the inner face; stems glabrous to densely pubescent but never lanate................................................................................................................................................5

5. Pollinaria lacking tooth on translator arms; stem with long spreading indumentums ........................................... Oxypetalum martii

- Pollinaria with well-developed tooth on translator arms; indumentum variable...............................................................................6

6. Leaves ovate with a cordate base, distinctly petiolate; style-head appendages slender, divided for most of their length................... ......................................................................................................................................................................... Oxypetalum boliviense

- Leaves oblong with a truncate base, subsessile to shortly petiolate; style-head appendages united for about half their length ......... ......................................................................................................................................................................... Oxypetalum capitatum

7. Style-head appendages not exserted beyond head of gynostegium; corona of 5 pubescent overlapping lobes forming a ring in the throat of the corolla tube...................................................................................................................................... Oxypetalum retusum

- Style-head appendages exserted well beyond head of gynostegium; corona not as above................................................................8

8. Style-head with 5–7 slender filiform appendages..............................................................................................................................9

- Style-head appendage bifid, slender or fleshy and expanded...........................................................................................................12

9. Style-head appendages red or dark purple; corona lobes arising from base of corolla tube ......................... Oxypetalum attenuatum

- Style-head appendages white or cream; corona lobes arising at base of gynostegium....................................................................10

10. Style-head appendages 7, all of equal size; corona lobes attenuate, with shorter tooth on inner face; central dry valley system associated with Rio Grande ............................................................................................................................. Oxypetalum heptalobum

- Style-head appendages generally 5, if 7, then the 2 central ones much more slender than the 5 outer ones...................................11

11. Corona lobes with outer portion and inner tooth equal in length; northerly Yungas or dry valleys in La Paz Dept and around Independencia.......................................................................................................................................................... Oxypetalum pentaseta

- Corona lobes fleshy, lacking appendage on inner face; Tucumán forest in Chuquisaca and Tarija ................... Oxypetalum fiebrigii

12. Style-head appendages purple..........................................................................................................................................................13

- Style-head appendages white or cream............................................................................................................................................14

13. Corolla lobes triangular, strongly reflexed at anthesis; corona lobes truncate .................................................. Oxypetalum balansae

- Corolla lobes linear and parallel-sided for most of their length, spreading radially; corona lobes acute ............................................ ................................................................................................................................................................ Oxypetalum flavopurpureum

14. Style-head appendages at least 5 mm long, filiform........................................................................................................................15

- Style-head appendages 4 mm or less, more robust...........................................................................................................................17

15. Corolla lobes subglabrous; pollinaria with hyaline tooth on translator arms........................................... Oxypetalum brachystemma

- Corolla lobes pubescent to bearded; pollinaria lacking teeth on translator arms.............................................................................16

16. Corolla tube significantly longer than broad; corona lobes with triangular tooth on inner face; corpusculum elongate, ca. 0.75 mm long.................................................................................................................................................................. Oxypetalum erianthum

- Corolla tube almost as broad as long; corona lobes generally lacking tooth on inner face; corpusculum ca. 0.55 mm long.............. .................................................................................................................................................................... Oxypetalum dombeyanum

17. Style-head appendages expanded, fleshy.........................................................................................................................................18

- Style-appendages not expanded or fleshy........................................................................................................................................19

18. Flowers at least 1 cm long, arranged in diffuse open inflorescences ......................................................Oxypetyalum dactylostelma

- Flowers 0.5–1 cm long, arranged in congested heads; Tucumán forest belt from Santa Cruz to Tarija .............. Oxypetalum fuscum

19. Inflorescence with peduncle at least 2 cm long; style-head appendage conical, the lobes not divergent ..... Oxypetalum urceolatum

- Inflorescences subsessile, peduncle less than 1 cm long; style-head appendage with divergent lobes ........... Oxypetalum pearsonii