MALACEAE • 135 



the distribution nor the abundance of more than a few is known. 

 Forty-seven species have been described and named from origi- 

 nal Illinois material, but most of these and many of the others 

 are known only from isolated or limited collections. The 26 

 species given in the following key, without distinction as to tree 

 or shrub forms, are known to have either wide distribution or 

 local abundance and are those most apt to be encountered. 



Among the hawthorns there is much variation in the obvious 

 characters relied upon, in other groups, for species identification. 

 Species normally treelike often assume a shrubby habit. Leaf 

 shape may vary greatly, even on the same branch; and varia- 

 tions in finer characters, such as lobing, serration, pubescence, 

 twig color, and size, texture and color of fruit, add confusion. 



Major characters used in distinguishing species are, in the 

 order of their commonly recognized importance, (1) the color 

 of the anthers, (2) the number of the stamens, (3) the pu- 

 bescence character of the corymbs at flowering time, and (4) 

 the general shape of the leaf. Broader characters used in the 

 grouping of species include (1) leaf serration and lobing, (2) 

 leaf texture, (3) leaf veining, (4) foliage color, (5) size, shape 

 and color of the fruit, and (6) the number and shape of the 

 nutlets. 



Accurate naming of a hawthorn is a task that taxes even the 

 discriminative judgment of an experienced taxonomist. Careful 

 and prolonged observation of the unknown plant must be 

 coupled with keen appreciation of characteristics as they appear 

 or change from season to season. For any but the most com- 

 mon species, the help of an expert should be sought, and one 

 should submit for examination an adequate series of specimens 

 showing the full growing season's changes from flowers to 

 ripe fruit. 



Key to Common Hawthorn Species 



A. Leaf veins extending only to the points of lobes or teeth ; 

 leaves usually only slightly, if at all, lobed. 

 B. Leaf widest at or beyond the middle, the base wedge 

 shaped. 

 C. Widest part of the leaf beyond the middle. 



1. Leaves lustrous; veins not deeply impressed above. 

 2. Thorns 3 to 4 inches long, midrib greenish (fig. 



31) C. Crus-galli L. 



2. Thorns 1 to 2 inches long, midrib yellow 



C. arduennae Sarg. 



