274 UNIVERSITY OF COLORADO STUDIES 



3C. Pedicels densely villous at flowering time; becoming nearly glabrous; leaves ob- 

 ovate, wedge-shaped at base. Crataegus laurentiana Sarg. 



"St. Lawrence Thornapple " 



4a. Shoots becoming glabrous or nearly so at close of first year; leaf serrations glandular. 



(5) 

 4b. Shoots villous or pubescent throughout the first year; leaf serrations not glandular. 



(6) 



5a. Leaves at maturity perfectly glabrous; fruit golden yellow.' 



Crataegus chrysocarpa Ashe. 

 "Golden Thornapple" 



5b. Leaves at maturity with scattered villous pubescence below, especially on the veins; 

 fruit dark red. Crataegus doddsii Ramaley 



"Thick-leaved Thornapple" 



6a. Petiole about £ the length of the blade; leaf-apex often obtuse. 



Crataegus occidentalis Britt. 

 "Western Thornapple" 



6b. Petiole about J to J the length of the blade; leaf -apex often somewhat truncate. 



Crataegus coloradoides Ramaley. 

 "Canyon Thornapple" 



7a. Leaves ovate, simply serrate or crenate, 2 to 4 cm. broad. Crataegus rivularis Nutt. 



"River -bank Thornapple" 



7b. Leaves lanceolate, serrate, sometimes obscurely lobed; only 1 to 2 cm. broad (generally 

 about 1 . 5 cm.) Crataegus saligna Greene 



"Small-leaved Thornapple" 



Genus 15. PRUNUS, Plum and Cherry 



Four species of Prunus are recognized as occurring in Colorado. 

 One is the common wild plum so abundant at canyon mouths in the 

 foothills; the others are cherries. Of the latter, Prunus besseyi is a 

 dwarf species, often a mere trailing or prostrate shrub. 



ia. Flowers and fruits in long racemes; fruit black when ripe. 



Prunus melanocarpa (A. Nels.) Rydb. 

 "Choke Cherry" 



lb. Flowers and fruits in short umbels or corymbs. (2) 



2a. Leaves bright green and shining above; fruit red, 5 to 7 mm. (about J in.), in diameter. 



Prunus pennsylvanica Linn. f. 

 "Wild Red Cherry" 



2b. Leaves dull green above; fruit 20 to 25 mm. (f to 1 in.) in diameter. 



Prunus americana Marsh. 

 "Wild Plum" 



•These characters are taken from the original description but do not agree with certain specimens 

 credited to this species. 



