5. Fraxinus L. (ash)(G. N. Miller, 1955)

Plants trees (rarely shrubs elsewhere), to 40 m tall, dioecious or with some perfect flowers mixed with the pistillate and/or staminate ones (usually with mostly perfect flowers in F. quadrangulata; sometimes monoecious elsewhere). Trunk usually 1 (more following damage or upon resprouting after logging), the branches spreading to ascending, the bark gray, relatively thick, developing a network of ridges and diamond-shaped furrows, sometimes becoming scaly with age. Twigs relatively stout, gray to brown, glabrous or hairy, more or less circular to sharply 4-angled in cross-section, with raised leaf scars and inconspicuous to conspicuous, pale lenticels. Terminal buds usually closely flanked by the uppermost, shorter pair of axillary buds, variously shaped, with several, overlapping, sharply pointed scales, the axillary buds also variously shaped. Leaves opposite, short- to moderately petiolate. Leaf blades odd-pinnately compound with mostly 5–11 leaflets, to 40 cm long and 25 cm wide, more or less oval in outline, the leaflets mostly short-stalked, variously shaped, angled or tapered to the sharply pointed tip, rounded or angled at the sometimes asymmetric base, the margins entire or shallowly toothed, the surfaces variously glabrous or hairy, the upper surface medium to dark green, the undersurface pale or lighter green. Inflorescences axillary, many-flowered, appearing yellowish green to green or occasionally purplish red (pistillate) or red to purplish red (staminate, shedding yellow pollen), consisting of fascicles, clusters, or short racemes, these usually grouped into small panicles, those with staminate flowers usually appearing denser and consisting of more capitate clusters than those with pistillate flowers, produced from 1-year-old branches, developing before the leaves or as the leaves expand, some of the branch points with small, scalelike bracts (these shed early), the flowers stalked, not fragrant. Calyces absent or, if present, then sometimes shed early, shallowly to deeply 4-lobed (sometimes cleft nearly to the base along 1 side), 0.5–1.5 mm long (sometimes to 4 mm in pistillate flowers of F. profunda), the lobes or teeth narrowly triangular to triangular. Corollas absent (present and with 2–6 petals or deep lobes elsewhere). Style 1–3 mm long, with a pair of ascending branches at the tip. Fruits slender, elongate samaras, usually pendant, 25–80 mm long (including the wing), the body flattened or more commonly turgid, with a conspicuous, slender, sometimes somewhat asymmetric wing at the tip, the wing extending narrowly and laterally along the body, pale green, turning straw-colored to grayish tan or brown with age. Sixty to 65 species, North America, Central America, Caribbean Islands, Europe, Africa, Asia, Malaysia; most diverse in temperate regions.

Ashes are common components of most upland and bottomland forests. The wood is of commercial importance for its great strength and shock resistance, and is used in furniture, flooring, veneers, baseball bats, hockey sticks, canoe paddles, other implement handles, and handcrafts. Moerman (1998) noted that Native Americans also used various parts of the plants medicinally, ceremoniously, and as a minor food source. The windborne pollen of ashes is considered a seasonally important cause of hayfever. White and green ash are both easily transplanted and commonly grown ornamentally, with green ash being used more commonly because of its faster growth. The foliage turns bright yellow in the autumn. Cultivars are available for both species featuring lack of fruit production and, in white ash selections, purple fall foliage. Both species, however are subject to a number of disease and insect pest problems. The Eurasian Fraxinus ornus L. (flowering ash, manna ash) occasionally is planted in Missouri for its large, terminal panicles of fragrant flowers with slender, white petals, but is not known to escape from cultivation.

All North American ashes have become seriously threatened in recent years by the spread of a destructive, invasive, wood-boring beetle from Asia called the emerald ash borer (Agrilus planipennis Fairmaire). This species was first detected in 2002 in southeastern Michigan and soon after in adjacent Ontario, Canada (Poland and McCullough, 2006). It presumably entered North America as a contaminant in wood packing material or pallets used in the transport of other imports from China, and it has since spread into portions of Illinois, Indiana, Ohio, West Virginia, Virginia, Maryland, and Pennsylvania. The first report for Missouri was in 2008 from the southeastern portion of the state (Wayne County), and by 2012 the pest had been documented from the adjacent counties Madison and Reynolds, as well as from western Missouri in Platte County. According to the official emerald ash borer website (http://www.emeraldashborer.info), more than 20 million trees have been killed thus far. Adult females of A. planipennis deposit eggs in bark crevices of ash trees during the summer. The larvae form elaborate, meandering, S-shaped tunnels under the bark, feeding primarily on the phloem tissues. This results in various symptoms, including branch dieback, peeling and splitting of the bark, sparse foliage, anomalous branching, and eventually death (R. Lawrence, 2005). First- or second-year larvae pupate to form adults that emerge through the bark in the spring, leaving characteristic D-shaped exit holes. Efforts currently are underway to develop biological controls (mainly other insects and fungi that might parasitize emerald ash borer). However, this insect pathogen has demonstrated an ability for relatively rapid long-distance dispersal into new habitats, apparently by the transport of infested ash saplings and firewood by unsuspecting humans (Muirhead et al., 2006).