Whitespire Senior gray birch is a cultivar of the gray birch propagated by tissue culture or vegetative propagation from an original tree selected for its resistance to bronze birch borer. It is considered distinct in the trade from Whitespire gray birch, a related cultivar that may be propagated from seed and may or may not be as resistant to the birch borer. Both cultivars are more tolerant of the heat in the Chicago region than other varieties of white-barked birch. About half of the birch trees at the Chicago Botanic Garden are one of these two cultivars.

The primary ornamental feature of birch trees is the bark. Many of the common names of birch trees refer to the color of the bark -- white, gray, yellow or red. Another signature bark characteristic is its habit of separating into thin sheets; Native Americans used this property to harvest the bark from fallen paperbark birch trees to make canoes, bowls and shelter -- practical as well as beautiful. A strong secondary ornamental feature is the usually colorful golden fall foliage. Given their preference for cool weather and acid soil and their susceptibility to bronze birch borer infestations, birch trees can be challenging to cultivate in the Chicago region.

The genus Betula includes an indeterminate number of species of the birch tree; estimates range from 30-60. They are native to the cooler, temperate and sub-polar regions of Asia, Europe and North America -- generally preferring long cold winters and short mild summers. The Chicago Botanic Garden's collection contains more than 40 varieties among its more than 500 birch trees.