8 TEXAS RESEARCH FOUNDATION: CONTRIBUTIONS, VOLUME 5 
The pubescence in the genus is distinctive, but very difficult to characterize 
in terms which make it useful for classification. Two sections based on types of 
pubescence would appear to reflect natural affinities better than the two sectional 
divisions based on terminal and axillary inflorescences. Genetical studies are 
needed to help clarify these and other problems. 
The key to sections and series is designed to expedite the use of the general key. 
Key to Sections and Series 
Inflorescences terminal, pyramidal-paniculate................-..-..0+--0+e000: 
peeeeS REC oo er a Section I, Series 1-10, pp. 12-18, 22-123. 
Inflorescences axillary............ Section II, Series 11-23, pp. 18-22, 123-192. 
SECTION I 
Inflorescences terminal, pyramidal-paniculate 
Anthors versatile... 0 SE ea Series 1-2, pp. 22-33. 
Athos eek ee eee. 2s Series 3-10, pp. 32-123. 
Series 1-2 
Ovules 8-14 (19), uniseriate, biseriate or pluriseriate....... Series 1, pp. 22-32. 
1. P. trichogyne. 
2. P. chrysophylla. 
3. P. acuminata. 
4. P. papillosa. 
5. P. pyramidalis. 
Ovules 5 or 6, aniseriate,.-.. | oo Series 2, pp. 32-33. 
6. P. panamensis. 
Series 3-10 
Pubescence of branchlets usually rather coarse and con- 
spicuous, the hairs mostly erect, sometimes appressed on 
undersurface ‘of leaves coe eg ee ae Series 3, pp. 32-61. 
7. P. columnaris. 
8. P. sessilifolia. 
9. P. chiapensis. 
10. P: rufa: 
ll. P. prionophylla. 
12. P. parvifolia. 
13. P. serrulata. 
14. P. Eggersiana. 
15. P. amazonica. 
16. P. belizensis. 
17. P. aeruginosa. 
Pubescence of branchlets and undersurface of leaves fine 
and inconspicuous, the hairs usually closely appressed . Series 4-10, pp. 61-123. 
