Apr., 1923] GLEASON — VERNONIA IN NORTH AMERICA 189 



bescence of the cauline leaves and differ from them chiefly in size. The head 

 is pediceled if separated from the bract by an obvious internode, and the 

 inflorescence is then a scorpioid raceme. If this internode is reduced, the 

 head is sessile and the cluster becomes a scorpioid spike. The clusters may 

 be straight or flexuous, long or short, crowded or loose, with heads ranging 

 from 2 to 25 in number. As a result of the straightening of the sympodial 

 axis, the heads appear lateral and are usually placed about 90 around the 

 axis from the bracteal leaf. 



The leafy scorpioid cyme is found in 57 species, ranging throughout the 

 West Indies and on the continent extending north into southern Mexico. 

 Species with leafless cymes, 63 in number, occur commonly on the continent 

 from Panama to New England. From this region four have crossed the 

 narrow gulf east of Yucatan and entered Cuba; one has reached the Bahamas 

 from Florida; one is endemic to St. Vincent, and another reaches Trinidad 

 and the neighboring islands. In general, the distribution of the latter group 

 is continental, of the former Antillean. 



Perhaps the simplest type of the primitive leafy inflorescence is found 

 in the species-group Graciles, in which the cymes are stemlike and quite 

 undifferentiated from the truly vegetative portion of the stem, with 

 bracteal leaves closely resembling the cauline in size and shape. Species 

 of this group are almost entirely South American, ranging, according to 

 Ekman, from Colombia to eastern Brazil. One species only, V. gracilis 

 H. B. K. var. tomentosa Ekman, of Bequia, occurs in our range. 



A second group, with almost equally simple inflorescence, composed 

 of long, irregular, branching cymes, with long internodes and lea: ike bracts, 

 is the Argyropappae, of tropical South America, Central America, and 

 southern Mexico. The South American origin of the group may be assumed. 

 From there, V. remotiflora Rich, has been introduced into St. Thomas; 

 V. acilepis Benth. is endemic to Costa Rica, and V. argyropappa Buek 

 extends from Peru to Mexico. Two offshoots of the latter have arisen in 

 Mexico, V. hirsutivena Gleason in Yucatan and V. ctenophora Gleason in 

 Campeche, differing in minor structural details. 



It will be observed that these two groups, simplest in structure, are 

 distributed primarily in South America and that only a part of their species 

 reach North America, although among these are three endemic species and 

 one endemic variety. 



A third group of similar primitive structure as to inflorescence is the 

 Schiedeanae, of Central America and southern Mexico. While its members 

 differ sharply from the preceding group in their large heads, the peculiar 

 development and specialization of the involucral scales, and the absence 

 of foliar resin dots, they retain the simple cymes and broad, heavy leaves, 

 and may possibly be derived from it. V. vernicosa Klatt, with narrow 

 acuminate scales, appears to be the simplest and is endemic to Costa Rica. 

 V. Seemanniana Steetz follows in Costa Rica, with broad, obtuse scales, 



