36 HYDRANGEACEAE 



Key to the Genera 



Flowers with small petals and 8 to 10 stamens, the hypanthium 



ribbed in fruit Hydrangea 



Flowers with large petals and 12 to 16 stamens, the hypanthium 



in fruit not ribbed Philadelphus 



HYDRANGEA (Gronovius) Linnaeus 

 The Hydrangeas 



The hydrangeas are shrubs with opposite leaves and perfect 

 flowers borne in cymes. The flowers have 4 or 5 sepals, minute 

 except in the sterile flowers, where they are enlarged and petal- 

 like. There are 4 or 5 petals and 8 or 10 stamens. Each inferior 

 ovary consists of 2 to 4 united carpels and has the same number 

 of cells. Styles are wanting, but there are 2 to 4 stigmas. The 

 capsule is membranous walled and open at the top and contains 

 numerous seeds. The genus is represented in Illinois by the 

 following species. 



Key to the Hydrangea Species 



Leaves glabrous or with only scattered hairs H. arborescens 



Leaves densely grayish-tomentose on the underside H. cinerea 



HYDRANGEA ARBORESCENS Linnaeus 

 Hydrangea Smooth Hydrangea 



The Smooth Hydrangea, fig. 18, is a shrub which grows in 

 clumps, generally to about 3 feet, seldom as much as 6 feet, high. 

 Its old stems are covered by shreddy bark and its pubescent 

 branchlets bear opposite, rather large leaves which are ovate 

 or nearly orbicular. The leaf blades, supported on slender 

 petioles 1 to 4 inches long, are short-acuminate at the apex, cor- 

 date or rounded at the base, 3 to 6 inches long by nearly as 

 wide, and sharply dentate or serrate on the margins. The upper 

 surface often is more or less sparsely pubescent, the lower sur- 

 face more or less pubescent on the main nerves and lighter green 

 than the upper. 



The small flowers appear in the latter part of June and in 

 July, standing in terminal cymes or cymelike, white clusters. 

 The flowers in the clusters are of two kinds, fertile and sterile, 

 the sterile being generally fewer and on the outer margins of 

 the clusters. Fertile flowers develop small, 2-celled capsules, 



