sinnott: endemism as a criterion of antiquity 163 



common forms; while those which occur in defmite groups, all 

 the members of which are closely related to one another, evidently 

 represent locally developed types, each group of genera the 

 nucleus for a new subfamily. 



An analysis of the genera essentially endemic in temperate 

 North America reveals the fact that practically all the woody 

 types occurring in it are apparently "relict" endemics. Carya, 

 Planera, Madura, Asimina, Umbelhtlaria, Sassafras, Dirca, Calyco- 

 carpiim, Rohinia, Ptelea, Nemopanthus, Ceanothus, Garrya, Sym- 

 phoricarpos and many other shrub and tree genera exist without 

 very near relatives in North America, and the conclusion that they 

 are representatives of a flora at one time much more widely 

 distributed is strikingly confirmed by fossil evidence, which 

 shows that species of many of them flourished in Europe or 

 Asia during Cretaceous or Tertiary time. That most of these 

 forms are indeed relicts, and may therefore claim a relatively 

 high degree of antiquity, seems certain. 



We have observed, however, that the great bulk of North 

 American endemic genera are herbaceous in habit. There are a 

 number of herbaceous genera, for the .most part poor in species, 

 among the relict endemics; but it is well worthy of note that these 

 are the decided exceptions, for the great majority of endemic 

 herbaceous genera are not distributed thus scatteringly through 

 the various families but occur in definite groups the members of 

 which are closely related to one another. Examples of such 

 grouping are: Stanleya, Thelypodium, and their allies; Lesquerella 

 and its allies; and Leavenworthia and its allies among the Cruci- 

 ferae: Eriogonum and its allies among the Polygonaceae : Sarra- 

 cenia and Darlingtonia among the Sarraceniaceae : Heuchera and 

 its allies among the Saxif ragaceae : Zizia and its allies among the 

 Umbelliferae : Pterospora and its allies among the Ericaceae: 

 Cryptanthe and its allies among the Borraginaceae: Agastache 

 and its allies among the Labiatae: Pentstemon and its allies; 

 and Castilleja, Orthocarpus, and their allies among the Scrophu- 

 lariaceae: Brickellia and its allies; Solidago, Bigelovia, and their 

 allies; Townsendia, Sericocarpus, and their allies; Silphiiim and 

 its allies; Rudbeckia and its allies; Madia, Hemizonia, and their 

 allies; Baeria, Eriophyllum, Hymenopappus and their allies; 

 Microseris, Krigia, and their allies and Lygodesmia, Troximon, and 



