1. Fraxinus americana L. (white ash)

Pl. 461 g–i; Map 2095

Plants trees to 30 m tall with an oval crown, dioecious or incompletely dioecious. Twigs circular in cross-section, unwinged, glabrous, sometimes somewhat glaucous, gray to brown with relatively inconspicuous, somewhat paler, circular to elongate lenticels, the leaf scars U- or V-shaped to nearly semicircular, deeply notched on the apical side, the associated lateral buds dark brown to more commonly black, relatively deeply sunken into the twig. Terminal buds 4–6 mm long, broadly ovoid to broadly conic, wider than long, rounded to bluntly pointed at the tip, dark reddish brown, usually covered with minute, peltate yellow to brownish yellow scales (the surface often appearing mealy), with 3 or 4 pairs of scales, the outermost pair relatively short and tightly appressed. Leaves (5–)9–30(–35) cm long, the petiole glabrous. Leaflets mostly (5)7(9), 2–15 cm long, 1–7 cm wide, variable in shape but mostly lanceolate to ovate or elliptic, rounded or angled to the sometimes slightly apically winged stalk (this mostly 8–12 mm long on the terminal leaflet and 2–9 mm long on lateral leaflets), relatively thin to slightly leathery, the upper surface glabrous, dull to slightly shiny, the undersurface glabrous or sparsely to moderately short-hairy when young, usually whitened, the margins entire or with blunt teeth. Calyces present, persistent at fruiting, 0.5–1.5 mm long. Fruits (19–)25–32(–38) mm long, the slender stalk 5–10 mm long, the body 5–11 mm long, 2–4 mm wide, slender, narrowly oblong in outline, not flattened, the wing 3–6 mm wide, narrowly oblanceolate to narrowly oblong-lanceolate, more or less rounded at the tip, less commonly with a small notch or bluntly pointed, extending less than 1/3 of the way along each side of the body. 2n=46. April–May.

Common throughout the state (eastern U.S. west to Nebraska, Colorado, and Texas; Canada, Mexico). Mesic to less commonly dry upland forests, edges of glades, bottomland forests, banks of streams, rivers, and spring branches, margins of ponds, lakes, and sinkhole ponds, bases and ledges of bluffs, and loess hill prairies; also pastures, roadsides, and disturbed areas.

Black-Schaefer and Beckmann (1989) observed that individual trees of white ash in their study sometimes switched from staminate to pistillate, or vice versa, or to mixed flowers from one season to the next. It is not clear how commonly this occurs or whether other ash species are capable of changing gender.

Several authors (Wright, 1944; Hardin and Beckmann, 1982) have described the cuticular structure of the leaflet undersurface as a useful character in distinguishing even sterile specimens of some ashes. White ash can be distinguished from the other Missouri ashes by the presence of minute papillae, usually with interconnecting ridges that form an intricate cuticular network. However, observation of this character requires 30× or greater magnification

The present treatment follows that of Hardin (1974) in not recognizing infraspecific taxa within F. americana, but differs in recognizing F. biltmoreana and F. smallii as segregate species. See the treatments of these two taxa for further discussion. Other variants outside Missouri, such as the ones with somewhat smaller leaves and fruits (var. microcarpa A. Gray, var. texensis A. Gray), also seem unworthy of formal taxonomic recognition.

White ash wood is preferred for baseball bats and various tool and implement handles and is used to a lesser extent for furniture. The species has landscaping value but may be more suited to larger areas than typical residential lots because of its large size and susceptibility to various diseases and insect pests. In nature, it tends to occur at somewhat drier sites than is typical for F. pennsylvanica. Its fruits mature as early as June and are wind-dispersed in autumn, with some persisting on the tree into winter. It also sometimes is cultivated in South America and in the Old World.