8 ILLINOIS NATURAL HISTORY SURVEY MANUAL 3 



families; and certain genera and species have been retained, 

 although they are not recognized as distinct in Rehder's Manual. 

 In cases such as these, also in instances where Rehder's usage 

 departs widely from that to be found in the familiar Seventh 

 Edition of Gray's New Manual of Botany or in Britton and 

 Brown's Illustrated Flora of the Northern United States, 

 Canada and the British Possessions, it has been possible to add 

 explanations which will enable the user of this fieldbook to 

 reconcile the differences. 



Excluded Species. — There are records of occurrence in 

 Illinois for a considerable number of shrub species not listed in 

 the text. In part they are printed reports of species that, ac- 

 cording to present understanding of range limits, ought not to 

 occiir within the state. In many instances it has not been pos- 

 sible to test such reports by examining specimens, and inability 

 to verify the reports has been considered adequate cause for 

 omitting the species. In other instances, in which specimens 

 could be seen, it was clear that records w^ere based either on mis- 

 determinations or on determinations according with older species 

 concepts. The occurrence of dubious species has been recorded 

 in part, also, by specimens deposited in herbariums. It is true 

 particularly of the older collections that the specimens, properly 

 named in accordance with botanical concepts extant at the time 

 they were collected, fit into newer species. Redetermination of 

 such material has unified it with the species treatment embodied 

 in this text. 



Naturalized Shrubs. — This manual is intended particularly 

 to cover the native shrubs, but a few naturalized shrubs have 

 been included. When w^hite men began to settle in Illinois, 

 they brought with them from their eastern homes shrubs which 

 they had grown there, some of which had been brought earlier 

 from Europe. Other shrubs were purchased from nurseries, to 

 decorate the bare prairie home sites. Some of these shrubs 

 made themselves so much at home that they reseeded in wild 

 habitats and have become naturalized members of our native 

 plant communities. A number of these shrubs have been given, 

 in this manual, the same full descriptions as have native species. 

 If, however, there is evidence that certain introduced shrubs 

 persisting in the wild state do not multiply sufficiently to insure 

 their permanent existence here, attention has been called to 

 them and to the fact that they may be encountered from time 



