374 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 52 



GROUP OF D. OPPOSITA 



The old collective species Aspidium conterminum Willd. included 

 the species D. opposita, D. coarctata, D. consanguinea, and D. paiia- 

 niensis, as delimited in my "Revision." While the typical forms of 

 D. consanguinea and D. coarctata are well marked from the allied 

 species by their whole habit, the line of separation between D. oppo- 

 sita and D. panamensis is more difficult to define. The collection of 

 these species in the U. S. National Herbarium is very rich in speci- 

 mens from Central America, Jamaica, and Cuba. Sorting these 

 specimens one can quickly take out the typical forms of the two 

 species. It then appears that the specimens of true D. opposita are 

 all from the Lesser Antilles, and those of D. panamensis from 

 Jamaica, Cuba, and mainly Central America. Besides these remains 

 a number of specimens, mostly from Mexico and Jamaica, which 

 may as well be referred to D. opposita as to D. panamensis. The 

 question, then, is whether these intermediate forms are to be con- 

 sidered as real, phylogenetic intermediates, connecting the two pro- 

 posed species, which in this case ought to be united into one very 

 variable species, or if they represent one or more additional species 

 intermediate between the two. To solve this question a still larger 

 number of specimens from more localities is necessary. I am in- 

 clined to believe that the whole series of forms includes at least 

 three or four species, each of which varies considerably in different 

 directions, especially in size ; thus, the large forms of D. opposita 

 very much resemble D. panamensis, and small forms of D. pana- 

 mensis similarly resemble D. opposita. Such doubtful forms show 

 some features easily seen by the experienced eye but described only 

 with difficulty. It is evident that all forms are of the same phylo- 

 genetic origin ; the richest development is reached in Central Amer- 

 ica, where D. panamensis rivals in size species of the group of D. 

 Sprengelii, while D. opposita of the Lesser Antilles is an insular 

 reduced form derived from the same ancestors. Using the modern 

 terminology, it may be said that the series of forms includes a num- 

 ber of elementary species in the sense of de Vries, some of which 

 seem to be fixed species, while others are at the present period in 

 a state of quick evolution. A more remote derivative from the same 

 ancestors is the common Brazilian form called D. opposita var. 

 rivulorum (Raddi), which I now consider a distinct, fixed species. 

 I shall here confine myself to pointing out some additional diflferent 

 forms, which I describe as varieties of the species adopted in my 

 "Revision," to which species I refer the whole number of specimens. 



