TAXONOMY OR CLASSIFICATION 153 



thought to be closely related genetically. The species of 

 a genus will show similarity in fundamental characters, 

 such as the structure of the flowers and fruit, and usually 

 also a similarity in habit, or general aspect. 



Familiar genera are the oaks, the pines, the asters, the golden- 

 rods; or, among grasses, the blue-grasses and the wheat-grasses, the 

 millets and the bromes. 



As genera do not exist in nature, but represent the 

 taxonomist's ideas as to groups of related species, botanists 

 may not agree as to the limits of genera. The size of 

 genera, that is, the number of species included, is some- 

 times a matter of convenience. Conservative botanists 

 would probably not recognize Panicum and Paspalum as 

 separate genera, when considering the generic characters 

 only, but each group contains such a large number of 

 species that the two have been kept distinct for conve- 

 nience. Some species are so different from their nearest 

 allies that they cannot be consistently grouped with 

 other species. Such a species stands as the sole rep- 

 resentative of its genus, and the genus to which it belongs 

 is called a monotypic genus. It not infrequently happens 

 that after a monotypic genus is established other species 

 are discovered, which are assigned to it, and it ceases to 

 be monotypic. In contrast with monotypic genera are 

 others, such as Panicum, Andropogon and Poa, with hun- 

 dreds of species. Large genera may sometimes be con- 

 veniently divided into smaller groups, such as subgenera 

 and sections. 



From a nomenclatorial standpoint the term monotypic is used 

 to indicate genera with only one species at the original place of 

 publication. Cook suggests the word haplotypic for such genera. 

 (Amer. Nat. 48:311. 1914.) 



