244 GLEASON: TAXONOMIC STUDIES IN VERNONIA 
6-7 mm. high, its scales irregularly but rather closely imbricate, 
the outer and middle with triangular-ovate or oblong appressed 
bases and long subulate tips, the inner linear-oblong, rather 
abruptly acuminate and most of them subulate-tipped, and all 
thinly pubescent with dark-colored hairs and sparsely resinous; 
achenes thinly pubescent, sharply ribbed, 1.5 mm. long; pappus 
- white, its bristles 4 mm. long, prominently barbellate, the paleae 
little wider than the bristles, 0.6 mm. long, sharply ciliate with 
salient teeth. 
Type: E. A. Goldman 508, collected at Apazota, Campeche, 
Mexico, December 30, 1900, and deposited in the United States 
National Herbarium as sheet 396871. 
Vernonia ctenophora is a member of the species-group Argyro- 
pappae, as indicated by the resinous-dotted leaves and the long 
subulate involucral scales. Within the group it is most closely 
related to V. hirsutivena Gleason, from which it is distinguished 
by the conspicuously barbellate pappus bristles, the sharply 
ciliate and shorter paleae, the thinly pubescent involucre and 
achenes, the comparatively thin pubescence on the veins, and the 
numerous resin-dots on the upper surface of the leaf. 
VERNONIA MISSURICA Raf. 
Vernonia illinoensis Gleason, Bull. N. Y. Bot. Gard. 4: 211. 
1906. 
Throughout its wide range, which is more extensive and covers 
more diverse environmental conditions than that of any other 
species in the United States, V. missurica exhibits a considerable 
variation in structure. This variation pertains chiefly to the 
inflorescence and leaf-pubescence and less to the characters of 
involucre and achene. | 
Judged from herbarium evidence and field experience, the 
species is best developed in Indiana, Illinois, and northern Mis- 
souri, where it is by all odds the most common species of the 
genus. Here the inflorescence is broad, freely branched, with 
many heads, and relatively flat, and the leaves are thinly but 
closely tomentose beneath with cinereous multilocular hairs 
which cover the surface and veins alike. Farther to the north- 
east, at the border of its range in Michigan and Ontario, the mullti- 
locular hairs on the leaf-surface are relatively fewer and usually 
