580 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Hairs of stem all incurved or appressed. 

 Capsule more or less pubescent on sides. 



Flowers 4 to 5 mm. long 7. P. magdalenae. 



Flowers 6 to 7 mm. long. 



Stems birsute-tomentose above 8. P. leptosperma. 



Stems barely puberulous above 27. P. oaxacana. 



Capsule merely ciliate at maturity. 

 Middle and upper leaves strongly reduced, 5 to 14 mm. long, linear 

 or lance-linear. 

 Aril with more or less distinct dorsal lobe, subpedicellate by the 



pointed base of seed 9. P. barbeyana. 



Aril without distinct dorsal lobe, subsessile. 



Aril with subglabrous umbo 10. P. zacatecana. 



Aril with densely pilose umbo 11. P. intricata. 



Middle and upper leaves not reduced, 15 to 31 mm. long. 

 Middle and upper leaves obovate-oblong, 4.5 to 7 mm. wide. 



12. P. palmeri. 

 Middle and upper leaves linear, 1.5 to 3 mm. wide. 



13. P. racemosa. 

 Hairs of stem (at least in part) wide-spreading. 



Hairs of stem all short and wide-spreading; leaves not reticul;\te. 



14. P. rectipilis. 

 Hairs of stem partly long and spreading, partly short and incurved; 



leaves reticulate. 

 Middle and upper leaves linear or linear-lanceolate, 1.8 to 4 mm. wide. 



21. P. retifolia. 

 Middle and upper leaves oblong-lanceolate or oval, 4.5 to 16 mm. wide. 



22. P. amphothrix. 

 Aril larger, the depth of the lobed or lobulate scarious margin equaling or 

 exceeding the height of the corneous umbo. 

 Capsule merely ciliate at maturity ; aril not veil-like. 

 Upper leaves linear to narrowly lanceolate. 

 Stems incurved-puberulous. 

 Upper leaves strongly reduced, 5 to 14 (23) mm. long. 



15. P. reducta. 



Upper leaves not reduced, 17 to 36 mm. long 16. P. longa. 



Stems sparsely spreading-pubescent, glabrate 17. P. neurocarpa. 



Upper leaves ovate to elliptic-oblong. 



Wings 6 to 6.5 mm. long 18. P. oophylla. 



Wings 4 to 5 mm. long. 



Scarious border of aril barely as deep as height of umbo ; keel 



purplish 19. P. brachyanthema. 



Scarious border of aril distinctly deeper than height of umbo; 



keel yellowish green 20. P. brandegeana. 



Capsule pubescent on sides at maturity or, if merely ciliate, then aril 

 veil-like. ^^ 



Hairs of stem (at least in part) wide-spreading. S 



Middle and upper leaves linear or linear-lanceolate, 1.8 to 4 mm.^^ 



wide 21. P. retifolia. 



Middle and upper leaves oblong-lanceolate or oval, 4.5 to 16 mm 

 wide 22. P. amphothrix. 



