Identification of native plants, by contrast, is often a surer thing; 

many states have floras of their native plants

•

Even better for the beginner are books specializing in one 
particular geographic area, such as Marin County

•

The majority of these i.d. books contain not only some 
illustrations, but 

dichotomous keys

for making a 

determination

•

The inexact part of this aspect of i.d. is because keys contain 
many inconsistencies and sometimes just plain mistakes

•

The other inexact part is that plants vary a lot in the wild, and 
no keys take all of the variation into account

•

For example, the genus 

Fragaria

(strawberry) has flowers with 

5 petals, but occasionally an individual will display 6 petals, 
instead. This could completely mislead the identifier because 
number of flower parts is heavily emphasized