The genus Crataegus, with some theories concerning the origin 
of its species* 
HARRY B. Brown 
Doubtless the genus Crataegus has puzzled systematic botan- 
ists more the past decade or two than has any other genus of 
phanerogamic plants. A number of careful workers have been 
studying the genus for several years but as yet only tentative con- 
clusions have been reached. 
In Gray’s Field, Forest, and Garden Botany, published in 1857, 
there was listed for the states east of the Mississippi River, twelve 
species and two varieties of Crataegus. This included both wild 
and cultivated species, Ten species and four varieties were listed 
in the edition of Gray’s Manual of Botany published in 1867. This 
included both wild species and species escaped from cultivation. In 
Chapman’s Flora of the Southern United States, published in 1860, 
eleven species and one variety were described. These were largely 
the same as the species described in Gray’s Manual, only three 
being different. In Coulter's Manual of the Botany of the Rocky 
Mountain Region, published in 1885, four species were described ; 
two of these were included in Gray’s Manual. In the Cayuga 
Flora, published in 1886, there were six species and one variety ; 
this included the species of the Cayuga Lake basin. Focke’s 
estimate in Engler & Prantl, Die Natirlichen Pflanzenfamilien, 
published in 1888, was that there were thirty to forty species grow- 
ing in the north temperate zone. In the edition of Gray’s Manual 
issued in 1889, there were only ten species and four varieties de- 
scribed. Chapman’s Flora of the Southern United States, pub- 
lished in 1897, gives but fifteen species coming within its range, 
but about this time something happened to the genus, apparently 
— species seemed suddenly to become much more abundant. In 
Britton’s Manual, issued in 1901, thirty-one species were described. 
This covered the northern states and extended westward to about 
the 1ooth meridian, In Small’s Flora of the Southeastern United 
* Contribution from the Department of Botany of Cornell University, No, 139. 
251 
