5. Fraxinus quadrangulata Michx. (blue ash)

Pl. 461 c, d; Map 2099

Plants trees to 30 m tall (usually much shorter) with a narrow, rounded crown, with all or most of the flowers perfect. Twigs strongly 4-angled (square) in cross-section, the angles sometimes with narrow, corky wings, glabrous or more commonly minutely velvety-hairy when young, not glaucous, gray to reddish brown, eventually becoming tan to gray with age (as they expand to become more circular), with relatively conspicuous, pale, oval lenticels, the leaf scars broadly concave on the apical side on both new and older twigs. Terminal buds 4–7 mm long, ovoid to conic, slightly longer than wide, mostly bluntly pointed at the tip, greenish gray to brownish gray or reddish brown, velvety-hairy, with usually 3 pairs of scales, the outermost pair relatively long and loosely appressed. Leaves 8–30 cm long, the petiole glabrous or minutely hairy. Leaflets (5–)7–11, 4–12 cm long, 1.5–6.5 cm wide, mostly lanceolate to narrowly ovate or ovate, rounded or broadly angled (often asymmetrically so) above the usually narrowly winged stalk (this mostly 1–6 mm long on the terminal and lateral leaflets), relatively thick and somewhat leathery, velvety-hairy when expanding, at maturity the upper surface glabrous or nearly so, somewhat shiny, the undersurface moderately short-hairy toward the base along the main veins, yellowish green to pale green but not whitened, the margins with numerous, fine, blunt teeth. Calyces absent or, if present, shed early, 0.5–1.5 mm long. Fruits 25–45(–60) mm long, the slender stalk 4–10 mm long, the body 10–20 mm long, about 2 mm wide, narrowly lanceolate, relatively poorly differentiated from the wing and somewhat flattened, the wing 6–12 mm wide, narrowly oblanceolate to narrowly oblong, usually shallowly notched at the otherwise rounded to truncate tip, extending to the base of the body or nearly so. 2n=46. March–May.

Scattered to common in the Ozark and Ozark Border Divisions, northward locally in the eastern portion of the Glaciated Plains to Marion County; apparently absent from the remainder of the state (eastern U.S. west to Minnesota and Oklahoma; Canada). Mesic to dry upland forests, glades, savannas, and ledges and tops of bluffs; less commonly banks of streams and rivers, bases of bluffs, and bottomland forests; often on calcareous substrates.

The name blue ash refers to the fact that the inner bark or branches can be macerated in water to yield a blue dye, a practice of early pioneers (Steyermark, 1963). The wood is used commercially for purposes similar to those of white ash, but the species is less abundant and of less economic importance due to its smaller size. Blue ash has had limited use horticulturally as a species tolerant of drought and alkaline soils.