No. 484] CLOSELY RELATED SPECIES 



227 



and L. exocellata. The first of these species is very widely dis- 

 tributed in tropical America, growing on the upper surface of 

 thick and glossy leaves. The second species is less abundant 

 but nearly always occurs mixed with the first. 



"Among northern species Lophozia barbata and L. lyoni are 

 closely related and often grow together, although each retains 

 its distinctive characteristics. The same is true of Gymnomitrium 

 concinnatum and the much rarer G. corolloides; of Sphenolobu^ 

 exsectus and S. exsectcBformis; of Anthoceros levis and A. puncfains. 



"As a group of related species I might mention the ventricosa- 

 group of the genus Lophozia. This contains about half a dozen 

 closely related species, most of which are circumpolar in their 

 distribution. L. ventricosa, L. alpestris, L. porphyrolema, L. 

 longidens and L. confertifolia are all known from New England, 

 being most abundant in mountainous regions. Of these L. por- 

 phyroleiwa and L. longidem grow on rotten logs, and the others 

 on moist rocks, although L. longidens is equally at honu' on eitlier 

 substratum. Although I have no definite data that tlicsc species 

 actually grow mixed in North America, their ranp-s cdiiu iile to a 



been at all accufately .studied', ali.l I feel sm-e tliat further study 

 would considerably lengthen the short list I have given." 



Mr. A. A. Eaton has given me several examples from Equisetum 

 and Isoetes. "Equisetum jiuviatile is circumboreal in its distri- 

 bution. No third form stands between this and E. palustre, yet 

 the latter has practically the same range. E. scirpoides and E. 

 variegatvm arti a cognate pair, and yet both have in general the 

 same range throughout the northern part of both hemispheres. 

 E. variegatum has a variety, E. variegatum jessupi, distinguished 

 by anatomical characters. Its range, Vermont to Minnesota, 

 is quite covered by that of the species. E. hrvigaium has a near 

 relation, without an intermediate, in E. hiemale intermedium y. 

 and this on the other side is next to tlu> variety afme. The last 

 of the trio is wide-spread in northern North America and overlies 

 the other varieties, which also essentially coincide in their ranges. 

 E. arvense is found in Europe, Asia, N. America to Virginia and 



