Indochina (Gagnepain, 1925)

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 27

Key to the species of Indochina ( Laos, Cambodia, Vietnam)

( Trigonostemon adenocalyx is not included in the key, because there is no certain collection record for this area)

1. Venation pinnate.............................. 2

1. Venation triplinerved........................... 7

2. Petioles shorter than 3.5 cm ..................... 3

2. Petioles of at least some leaves longer than 3.5 cm ... 6

3. Leaves pubescent above; flowers mostly cauliflorous...................................... 9. T. flavidus

3. Leaves glabrous to slightly pubescent above; flowers never cauliflorous.................................. 4

4. Inflorescence longer, up to 30(– 55 in extreme cases) cm long; disc annular.................. 17. T. longifolius

4. Inflorescence up to 11.2 cm long; disc of 5 glands or lobes ............................................ 5

5. Pistillate sepals fringed with capitate glands; fruits glabrous.................................... 13. T. kerrii

5. Pistillate sepals with an entire margin; fruits pubescent.................................. 20. T. murtonii

6. Inflorescences racemose thyrses; pistillate sepals accres- cent; fruits densely hirsute, smooth... 15. T. lanceolatus

6. Inflorescences paniculate; pistillate sepals not accrescent; fruits glabrous, warty............ 23. T. philippinensis

7. Indumentum of simple and stellately bundled hairs.................................... 25. T. reidioides

7. Indumentum of only simple hairs.................. 8

8. Domatia present on the lower surface of at least some leaves............................. 10. T. fragilis

8. Domatia absent............................... 9

9. Translucent (oil?) dots absent in green parts... 16. T. lii

9. Translucent (oil?) dots present in green parts....... 10

10. Petals white...................... 8. T. eberhardtii

10. Petals yellow to orange........................ 11

11. Inflorescence axis very slender, up to 0.5 mm diam; often only very few flower buds present in the inflorescences in herbarium specimens................ 3. T. bonianus

11. Inflorescence axis stronger, up to 2 mm diam, often a large number of flowers present in the inflorescences in herbarium specimens............................ 12

12. Staminate flower buds globose; fruits hirsute......................................... 24. T. quocensis

12. Staminate flower buds conical; fruits glabrous...... 13

13. Fruits more or less warty............ 5. T. capitellatus

13. Fruits smooth.................. 30. T. viridissimus