Fraxinus quadrangulata
Blue Ash (Fraxinus quadrangulata)

Distribution Map to Right
Counties in blue contain tree

Shape and Distribution
Blue ash grows to a height of 60 to 80 feet, with a relatively short trunk reaching up to 3 feet in diameter. The crown can be rounded or irregular, with dead branches persisting on the main trunk.  Blue ash grows in upland mesic or dry woods, wooded slopes, and limestone cliffs. It occurs in the northern and central sections of Illinois, and along the Mississippi River on the western edge of the state down into southern Illinois.

Interesting Facts
Blue ash is also referred to as square-stemmed ash because its twigs and stems are square, distinguishing it from other ashes in the state. The name "blue ash" is a reference to the blue dye produced when the inner bark is placed in water and/or the sap, which turns bluish when exposed to air.

Identifying Features

Blue ash bark is bluish gray to brown gray. It is thickly furrowed and scaly, becoming shaggy with age. The shaggy, ridged bark of the mature tree is a distinctive characteristic. 
The twigs are light green-gray to brown and stout. They are square in cross-section - another distinguishing feature of blue ash. They can be either sparsely hairy or smooth, with a sap that turns bluish on exposure to air. 
The buds are rounded, slightly hairy and up to 1/2 inch long. 
The leaves are opposite, from 8-12 inches long, and pinnately compound with 5-11 leaflets. Leaflets are up to six inches long, lance-shaped with rounded or sometimes asymmetrical bases, and are coarsely toothed along the edges. They are light green and smooth on the upper surface and paler with sparse hair along the veins underneath.
Individual flowers have both male and female components (stamens and pistils) - botanists refer to this as a "perfect" flower. Flowers appear before leaf out as small, branched clusters of purplish flowers without petals. 
The fruits are oblong, winged, and enclose a single seed at the base. They are 1-2 inches in length, 1/2 inch broad, and dark green to gray. Songbirds and rodents eat the seeds.

Blue ash wood is heavy and hard. It is used for flooring. The inner bark produces a blue dye when crushed and placed in water.