32 PROCEEDINGS OF THE AMERICAN ACADEMY. 



b. Heads erect : slender annual. 



9. P. Pringlei, Robinson, Proc. Am. Acad, xxvii. 178. 



c. Heads erect : shrubs. 



1 0. P. Jonillense, Cass. '' Leaves 1 inch long, eglandular : petioles 

 6 to 7 lines long : scales of the involucre green." Diet. Sci. Nat. xliii. 

 57. Kleinia Juridlensis, HBK. Nov. Gen. & Spec. iv. 156, t. 356, whence 

 description. 



11. P. Nelsonii. Branching shrub, 1 to 2 feet high: stems terete, 

 striate, purple : leaves chiefly opposite, rather small and distant ; blade 

 elliptic or oblong, obtuse, 6 to 8 lines long, 2 to 3 lines broad, rather 

 gradually narrowed to a slender petiole (2 or 3 lines in length) ; glands 

 few on the margin or often only a single one at the end of the mid-nerve : 

 heads subcorymbose at the ends of the branches, 7 lines long, about 30- 

 flowered; scales of the involucre 5, linear-oblong, acute, purple especially 

 toward the summit, flat, marked with 2 rows of linear glands : corollas 

 dark purple, 3|- inches long : achenes strongly tapering, 3 to 3^ lines in 

 length. — Collected by E. W. Nelson^ in Oaxaca, between Panixtlahuaca 

 and Jaquila, altitude 5,000 feet, 26 February, 1895, no. 2399 ; also 

 between Nopala and Mixistepic, altitude 800 to 4,000 feet, March, 1895. 



* * Leaves rather broadly lanceolate, acute at both ends, slender-petioled. 



12. P. Palmeri, Rose, Contrib. U. S. Nat. Herb. i. 338, t. 34. 



* * * Leaves narrowly elliptic- or linear-oblong, obtuse or obtusish, gradually 

 narrowed to a sessile or short-petioled base. 



13. P. Seemannii, Schz. Bip. 1. c. 



14. P. obtusifolium, DC. 1. c. 650. 



15. P. decumbens, DC. 1. c. 



* * * * Leaves lance-linear, sessile, and amplexicaul. 



16. P. amplexicaule. Engelm. in Gray, PI. Wright, i. 120. 



***** Annuals or more commonly perennials, often shrubby at the base : 

 leaves very narrow ; truly linear or subulate, or lance-linear and acute or 

 acutish, sessile or subsessile, but not amplexicaul. 



4- Mexican species : corolla shallowly and regularly 5-toothed ; teeth deltoid : 

 achenes 2\ to o\ lines long : involucral scales green or glaucous, not dark 

 purple. 



17. P. scoparium, Gray. Leaves truly linear or terete, half a 

 line in breadth : peduncles inch or more in length. — PI. Wright, i. 119. 



18. P. pausodynum. Shrub: stems geniculate, branched, covered 

 with smooth reddish brown cortex : branchlets straight, erect, sulcate- 

 angulate, glaucescent : leaves scattered, linear-lanceolate, narrowed to an 

 obtusish apex, attenuate at the base to a short petiole, slightly succulent, 



