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ROBINSON AND GREENMAN. — GENUS POROPHYLLUM. 31 
V.—A PROVISIONAL KEY TO THE SPECIES OF PORO- 
PHYLLUM, RANGING NORTH OF THE ISTHMUS 
OF PANAMA. 
* Leaves with broad obtuse ovate or elliptic-oblong usually thin lamina, rather 
abruptly contracted at the base to a slender petiole. 
+ Heads very long; involucral scales at maturity 8 to 12 lines in length: pe- 
uncles conspicuously clavate: erect scarcely distinct annuals. 
1. P. macrocephalum, DC. Prodr. v. 648. 
2. P. ruderale, Cass. Dict. Sci. Nat. xliii. 56. 
3. P. ellipticum, Cass. 1. ¢. 
+ + Heads shorter; involucral scales about half inch in length: peduncles 
scarcely or not at all thickened toward the summit. 
++ Leaves with pellucid glands on the surface as well as at the margins. 
4. P. Ervendbergii, Gray, Proc. Am. Acad. xix. 35. 
5. P. nummularium, DC. |. c. 649. E 
++ ++ Glands of the leaves marginal or none. 
= Leaves broad, thickish: petioles rather short : probably a single species. 
6. P. viridiflorum, DC. 1. ¢. 648. 
@. P. Lindenii, Schz. Bip. in Seem. Bot. Herald, 308. 
= = Leaves thin and delicate. 
a. Heads nodding or almost pendulous. 
8. P. nutans. Leafy shrub with slender terete fuscous branches 
(marked with small light colored lenticels) and almost filiform branch- 
lets: leaves thin, elliptic, entire, or crenulate, obtuse but often mucronu- 
late at the apex, obtuse or acutish at the base, 8 to 14 lines long, half as 
broad ; marginal glands 4 to 6 on each side the leaf; petioles filiform, 3 
or 4 lines long: heads numerous, about 9 lines long: peduncles clustered 
at the ends of the branches in 3’s and 4’s: involucral scales 5, oblong, 
obtuse, 6 lines long, somewhat carinate, green, with double row of linear 
glands: flowers white or nearly so, 9 lines in length ; limb of the corolla 
sub-bilabiate, shallowly toothed: achenes 5 lines in length. — Collected 
C. G. Pringle, in mountains near Lake Chapala, 16 December, 1889, 
no. 2976, and by the same collector on rocky hills, Querendaro, Michoa- 
can, 25 October, 1892; later by E. W. Nelson, between Chilapa and 
Tixtla, Oaxaca, altitude 5,200 to 7,000 feet, no. 2170. Mr. Pringle’s 
Plants were at first determined as P. Ervendbergii and so distributed. 
On subsequent comparison with that species they appear thoroughly 
distinct, having only marginal glands on the leaves, nodding instead of 
€rect peduncles, less deeply cleft corolla, and longer achenes. 
