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Published In: Species Plantarum 2: 1056. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/4/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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2. Acer negundo L. (box elder, ash-leaved maple)

Pl. a, b; Map 805

Plants dioecious, small to medium trees to 25 m tall with ascending to spreading branches, the bark of young trees smooth and gray to light brown, eventually becoming separated into a network of long thin ridges on older trees. Twigs green to olive green, sometimes glaucous and appearing pale purple to purple, glabrous or densely hairy, the winter buds bluntly pointed at the tip, with 2 or 4 overlapping scales. Leaf blades 7–15 cm long, broadly triangular-ovate to oblong-ovate in general outline, pinnately compound, those of fertile branches and seedlings with 3–5 leaflets on a short rachis, those of vigorous vegetative shoots with 5–9 leaflets. Leaflets 5–10 cm long, oblong to ovate (terminal leaflet sometimes obovate), angled or tapered to sharply pointed tips, the upper surface light green, the undersurface pale grayish green, usually somewhat hairy when young, becoming sparsely hairy or glabrous at maturity, the margins coarsely and irregularly toothed and occasionally also with a few shallow lobes. Inflorescences produced before the leaves or during leaf development, the staminate ones umbellate clusters from buds along the branches, the individual flowers with long drooping stalks, the pistillate ones narrow drooping racemes from at or near branch tips. Calyces 1–3 mm long, the sepals fused only at the very base, the 5 lobes obovate to narrowly oblong-elliptic, rounded at the tips, yellowish green, hairy. Petals absent. Staminate flowers with 3–6 stamens and lacking a nectar disk. Pistillate flowers with the ovary glabrous or less commonly hairy. Fruits dispersing long after the leaves are mature, often not until the following autumn, the samaras 2.5–4.5 cm long, glabrous or less commonly hairy, the wings 2–4 cm long, spreading at less than a 90° angle. 2n=26. April–May.

Common nearly throughout Missouri (U.S., Canada, Mexico, Guatemala). Bottomland forests, banks of streams, mesic upland forests in bottoms of ravines, and bases of bluffs; also shaded ditches and moist roadsides.

Box elder has fallen into disfavor horticulturally, for although it grows easily under a variety of site conditions, the branches of older trees break easily during storms, and the trees are susceptible to a number of fungal diseases and insect pests, notably the box elder bug, Leptocoris trivittatus (Say) (Wagner, 1975). The leaves turn yellow in the autumn and are shed earlier than those of most other trees. Unlike other Missouri species of Acer, which are pollinated by both insects and wind, the flowers of A. negundo are only wind-pollinated and are a cause of hay fever during the spring.

Acer negundo has been treated as consisting of a number of varieties by many botanists (Murray, 1975), each occupying a portion of the species’ overall distribution. Four of these taxa were accepted as occurring in Missouri by Steyermark (1963), who nevertheless had difficulties with infraspecific determinations of some specimens. For convenience, the species is here treated as a complex of only two varieties, which allows nearly all specimens to be classified relatively easily.



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