Acer negundo
Acer negundo, also known as the box elder, boxelder maple, Manitoba maple or ash-leaved maple, is a species of maple native to North America from Canada to Honduras. It is a fast-growing, short-lived tree with opposite, ash-like compound leaves. It is sometimes considered a weedy or invasive species, and has been naturalized throughout much of the world, including South America, Australia, New Zealand, South Africa, much of Europe, and parts of Asia.
Description
Acer negundo is a fast-growing and fairly short-lived tree that grows up to tall, with a trunk diameter of, rarely up to diameter. It often has several trunks and can form impenetrable thickets. The typical lifespan of box elder is 60 - 75 years. Under exceptionally favorable conditions, it may live to 100 years.The shoots are green, often with a whitish to pink or violet waxy coating when young. Branches are smooth, somewhat brittle, and tend to retain a fresh green color rather than forming a bark of dead, protective tissue. The bark on its trunks is pale gray or light brown, deeply cleft into broad ridges, and scaly.
Unlike most other maples, Acer negundo has pinnately compound leaves that usually have three to seven leaflets. Simple leaves are also occasionally present; technically, these are single-leaflet compound leaves. Although some other maples have trifoliate leaves, only A. negundo regularly displays more than three leaflets. The leaflets are about long and wide with slightly serrate margins. Leaves have a translucent light green color and turn yellow in the fall.
The yellow-green flowers are small and appear in early spring, with staminate flowers in clusters on slender pedicels and pistillate flowers on drooping racemes long.
The fruit is a schizocarp of two single-seeded, winged samaras on drooping racemes. Each seed is slender, long, with a incurved wing; they drop in autumn or they may persist through winter. Seeds are usually both prolific and fertile.
Unlike most other maples, A. negundo is fully dioecious and both a male and female tree are needed for reproduction to occur. The male and female flowers appear on separate plants, with males featuring clusters that generally have four flowers together, while females appear as a raceme.
Taxonomy
The Box elder is not in the Elder genus Sambucus in the family Adoxaceae. A few botanists treat boxelder maple in its own distinct genus but this is not widely accepted.Common names
Indicative of its familiarity to many people over a large geographic range, A. negundo has numerous common names. The names "box elder" and "boxelder maple" are based upon the similarity of its whitish wood to that of boxwood and the similarity of its pinnately compound leaves to those of some species of elder.Other common names are based upon this maple's similarity to ash, its preferred environment, its sugary sap, a description of its leaves, its binomial name, and so on. These names include "Manitoba maple", "ash-leaf maple", "cut-leaved maple", "three-leaf maple", "ash maple", "sugar maple", "negundo maple", and "river maple".
Names vary regionally. Box elder, boxelder maple, ash-leaved maple, and maple ash are among its common names in the United States. In Canada it is commonly known as Manitoba maple and occasionally as elf maple. In the British Isles it is known as box elder or ashleaf maple. In Russia it is known as American maple as well as ash-leaf maple.
Because of its leaflets' superficial similarity to those of poison ivy, Acer negundo saplings are often mistaken for the allergenic plant. While both poison ivy and Acer negundo have compound leaves composed of three leaflets with ragged edges, Acer negundo exhibits an opposite branching pattern, as opposed to the alternating pattern of poison ivy. Like poison ivy, Acer negundo is also a noted riparian species, and can often be found growing along riverbeds and in wet soils generally. For all these reasons, and despite their obvious differences, Acer negundo is sometimes referred to informally as the poison ivy tree.
Subspecies
Acer negundo is often divided into three or more subspecies, some of which were originally described as separate species. These are:- Acer negundo subsp. negundo, native from the Atlantic Coast to the Rocky Mountains.
- Acer negundo subsp. interior Sarg., with more leaf serration than the nominate subspecies and a more matte leaf surface, is native from Saskatchewan to New Mexico, between the eastern and western subspecies.
- Acer negundo var. arizonicum Sarg. is native to Arizona, New Mexico, and northern Mexico.
- Acer negundo subsp. californicum Sarg., with larger leaves with a velvety texture, is found in parts of California.
- Acer negundo subsp. mexicanum Wesm. is native to Mexico, Guatemala, and Honduras.
- Acer negundo var. texanum Pax is native to the southern United States from Virginia to New Mexico, and to northeastern Mexico.
- Acer negundo var. violaceum H.Jaeger is native to the Northeastern coastal United States and to the northern interior United States from the Ohio Valley to the Columbia River basin.
Distribution and habitat
Acer negundo is native across much of the United States and south-central Canada, and can be found as far south as Guatemala.Box Elder County, Utah is named for this tree, as is the town of Box Elder, South Dakota
Although native to North America, it is considered a weedy species in some areas, such as in parts of the Northeastern United States, and has increased greatly in these areas. In 1928, Joseph Illick, chief forester for the state of Pennsylvania, wrote in Pennsylvania Trees that box elder was "rare and localized" in the state. After World War II, box elder's rapid growth made it a popular landscaping tree in suburban housing developments despite its poor form, vulnerability to storm damage, and tendency to attract large numbers of box elder bugs. Intentional cultivation has thus made the tree far more abundant than it once was.
It can quickly colonize both cultivated and uncultivated areas and the range is therefore expanding both in North America and elsewhere. In Europe where it was introduced in 1688 as a park tree it is able to spread quickly and is considered an invasive species in parts of Central Europe, including Germany, the Czech Republic, Hungary, Slovenia, Poland and Russia where it can form mass growth in lowlands, disturbed areas, and riparian biomes on calcareous soils. It has also become naturalized in eastern China, is listed as a pest invasive species in some of the cooler areas of the Australian continent, and is invasive in the Rio de la Plata area.
This species prefers bright sunlight. It often grows on flood plains and other disturbed areas with ample water supply, such as riparian habitats. Human influence has greatly favored this species; it grows around houses and in hedges, as well as on disturbed ground and vacant lots.
Ecology
Several birds and some squirrels feed on the seeds. The evening grosbeak uses them extensively.The boxelder bug lays its eggs on all maples, but prefers this species, clustering the eggs in bark crevices. The rosy maple moth also lays its eggs on the leaves of maple trees, including Acer negundo. The larvae feed on the leaves, and in very dense populations can cause defoliation.
Small galls are formed on the leaves by a bladder mite, Aceria negundi. A gall midge, Contarinia negundinis joins and enlarges the galls of Aceria negundi. The midge sometimes creates a separate, tubular gall on the midrib or veins of the undersides of the leaves.
The cottony maple leaf scale, Pulvinaria acericola, occurs on the foliage of Acer negundo. A leaf spot fungus, Septoria negundinis creates black-ringed lesions on the leaves.
Cultivation
Although its weak wood, irregular form, and prolific seeding might make it seem like a poor choice for a landscape tree, A. negundo is one of the most common maples in cultivation. Long-term success has been noted as far north as Yellowknife. Many cultivars have been developed, such as:- 'Auratum' – yellowish leaves with smooth undersides
- 'Aureomarginatum' – creamy yellow leaf margins
- 'Baron' – Hardier & seedless variety
- 'Elegans' – distinctively convex leaves
- 'Flamingo' – pink and white variegation
- 'Pendulum' – with weeping branches.
- 'Variegatum' – creamy white leaf margins
- 'Violaceum' – younger shoots and branches have bluish color
Toxicity
Acer negundo pollen, which is released in winter or spring is a severe allergen.