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The Boxelder (Acer negundo) Story

Acer negundo Common names: boxelder, ash-leaf maple. Plant family: Aceraceae, maple family

Boxelder is a fairly common, rather weedy, tree native to the U.S. A. It is the most widely distributed North American maple, found mostly in the eastern half of the United States up through south-central Canada, but with a scattered range from coast to coast in the U. S. and south to the mountains of Mexico and Guatemala. Boxelder has been naturalized in New England, and eastern Canada; and in Washington and eastern Oregon1.

Description: Boxelder can grow to about 65 ft. (20 m) tall, but more often it is shrubby with no central trunk. It is short lived, about 60 years, and fast growing. The twigs are pale green to green-purple, with waxy bloom, cut plants resprout readily. The winter buds are blue to purplish, densely, finely white-hairy. The bud scales are opposite, and overlapping.

The roots are associated fungi known as with arbuscular mycorrhizae (AM), also known as endomycorrhizae.  Mycorrhizas are symbiotic associations between the roots of a plant and a fungus. These fungi form structures within root cells called arbuscules. Arbuscules are finely branched structures inside the outer cells of the root. The fungus helps extract nutrients, especially phosphorus, from soil and, in turn, uses carbohydrates manufactured by the plant. There are several different structural types of mycorrhizas. Arbuscular mycorrhizas are the most common type of root symbiosis. They occur in woody and herbaceous plants from ferns to trees and grasses. These fungi form a separate phylum of fungi, the Glomeromycota. They cannot grow except in symbiotic relationships and have been reclassified on the basis of DNA analysis, since they cannot be grown in culture the way other fungi can (i. e. penicillium and the like).

Acer Negundo leaves

The leaves of boxelder are opposite, and unlike any of our other maples, pinnately compound (divided), with 3-5 leaflets, sometimes up to 9 on young growth.  The first 3 leaflets are the most conspicuous and often look like poison ivy leaves. The leaf veins are conspicuous, hairy, and the margins of the leaflets are irregularly toothed. The leaves expand late-April to mid-May and, according to a paper written in 1874, the winter plant is leafless 184 days. However this time has probably become shorter due to climate change.

The flowers emerge just before the leaves, from March-April. They are reddish to green, small, and without petals. The petal-like parts are sepals, the flower parts normally outside of the petals. The sexes are on separate plants (dioecious).  The male flowers (anthers) are small, and dark, in umbrella-shaped clusters on large groups of elongated, drooping stalks (filaments). The female flowers are in drooping, unbranched clusters each on its own short stalk (racemes), the most conspicuous parts are the bright green, curving stigmas. Boxelder pollinated by wind.

Boxelder fruit is dry and consists of pairs of winged seeds (samaras), each 3-4.5 cm (roughly 1-1.5 inches) long, attached end to end, and splitting apart as they are dispersed. The seeds ripen Sept.-Oct. They are persistent on the tree and are dispersed throughout the winter. The seeds are eaten by a number of birds, rodents, rabbits, raccoons, deer and porcupines and other animals.

Ecology:

Wetland status: The USDA1 lists the wetland status of boxelder as FAC+ (a facultative wetland plant) meaning that while it can most often be found in wetlands, it is found in drier soils (uplands) about a third of the time.

Habitat: Boxelder is found in flood plains, moist soil of roadsides and edges. It tolerates a soil pH 5-8 (acid to fairly alkaline). It is tolerant of flooding, and anaerobic soil, saturated soil up to 75% of the growing season but also tolerates drought. It is also tolerant of soil compaction, demolition debris, concrete rubble, old blacktop and moderately tolerant of salt. It is listed as tolerant of shade in the USDA, NRCS database1 but as having a shade index of only 1.8 (intolerant) and being shaded out as canopy closes by (Hightshoe 1987)2.

Notes: The seeds, buds and flowers of boxelder are eaten by songbirds, squirrels, chipmunks and smaller rodents. The twigs eaten by rabbits. Boxelder is attached by  a number of fungi, including: Fomitopsis fraxineus (Perenniporia fraxinea is now the accepted name) a wood rot polypore. This is a woody, perennial bracket fungus, sometimes colonial, and very variable. It grows on the tree or on dead wood, the lower surface is at first bright white spongy-looking, upper surface brown, irregular and warty. It forms successive rings as it grows, broad at the base, with the outer margin irregularly wavy. This fungus is not edible. Boxelder is also infected by Verticillium albo-atrum, Verticillium wilt is visible as dead and dying leaves on infected plants but is similar to some environmental problems. The fungus Didymosporina aceris (syn. Marsonina truncatula; Deuteromycotina) causes two-toned tan and brown

Perenniporia fraxinea

Fritz Wohlfart 1962 Botanische Staatssammlung München

spots on the leaves.

 

Boxelder is a host tree of the very destructive Asian longhorn beetle, Anoplophora glabripennis. This is a large, 1-1.5 inch long, black insect with white markings and elongate black and white striped antennae. It lays its eggs in small pits or slits chewed into bark of the upper branches of a tree. The larvae tunnel into the wood and form extensive galleries through the sap and heartwood, they pupate near the surface of the wood and adult beetles chew a large exit hole 3/8-1/2 in., wide through the bark to the outside. Other symptoms of infestation are thin, sawdust like larval droppings in branch crotches and around the tree base. Infested trees must be cut, chipped and burned to prevent spread of the insect. The beetle arrived in raw wood pallets from China as early as the mid. 1980’s. It was first discovered in 1992 in Massapequa, Long Island. It presents a critical danger to the hardwood forest of the northeast.

Boxelder is also a host of the periodical cicada, Magicicada cassini. This cicada spends up to 17 years as an underground nymph, which lives on tree root sap. The nymphs mature together and the adults emerge all at once to mate. Females cut slits in the bark of small branches into which they lay their eggs, usually causing death of the branch tip. The larvae hatch and drop to the ground restarting the cycle. Tree damage can appear very extensive with many drooping, dead branch tips left by a cicada emergence. However, a study in 2002 found no significant decrease in growth due to this damage, at least to boxelder.

 

Magicicada cassini. Google Image

The following references give more information about boxelder.

1 http://plants.usda.gov/java/; See also: “Silvics of North America,” www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm

 Gary L. Hightshoe. 1987. Native Trees Shrubs, and Vines for Urban and Rural America: A Planting Design Manual for Environmental Designers.

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