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Scientific name: Anthophyta: Dicotyledonae: Rosales: Fabaceae:
Common Name: Information Sheet, Black Locust

Country: USA
State/District: MD
County: Montgomery
Date (D-M-Y): 14 - 4 - 2001

Photographer: E. M. Barrows

Identifier: E. M. Barrows
Collector: not applicable
Location: Bethesda, Maryland
Keywords: a Forest Ecology information sheet magenta flower pink flower red flower Eastern Redbud tree white flower
Additional Information:

Robinia pseudoacacia Carolus Linnaeus, Acacia, Black Locust, Common Locust, False Acacia, Locust, Robinier Faux-acacia (in Quebec), Yellow Locust, White Locust.

[locust, after locust trees of the Eurasian East, named such by colonists in Jamestown (Walker 1990, 211)] [Latin Robinia, after Jean Robin, 1550-1629, herbalist to Henry IV of France, and his son, Vespasian Robin, 1579-1662, who first cultivated the Black Locust in Europe; pseudoacacia, old generic name, false acacia, after usually evergreen trees of similar characteristics of biblical fame (Sutton & Sutton 1985, plates 129, 157; Walker 1990, 211; Kricher & Morrison 1998, 249)

Range.   Native to US.   Naturalized in many countries.

Habit.   Tree, up to 100 feet tall, often 40-60 feet tall.   Trunk: Up to 4 feet across. Some trees have clear straight boles and others have poorly developed trunks.   Crown: narrow, oblong cylindrical of irregular, more or less contorted branches.   Leaves: deciduous, pinnately compound leaves.   Thorns: up to 1 inch long. Sometimes forms thickets.   Flowers: fragrant white, May through June. Fruit: legume, smooth, flat.   New trees arise from root suckers and seeds.   Black Locusts are short lived, and seriously attacked by borers. Toxic to humans. Records of human poisoning are rare.

General roles in forests.   Black Locusts are autotrophs that generally live in forests, forest edges, successional areas, and yards.   Many kinds of organisms consume dead and living Black Locust fruits, leaves, roots, and stems.

Specific roles in forests.   Black Locusts are important in forest succession, as part of wildlife habitats, as food for other organisms, and ecological functioning of forests.   Black Locusts are common in some forests, along forest edges, and in fields that are becoming forests.   This species sometimes grows in pure stands.   It is expanding its range into more forests, moving into colder areas, partly perhaps due to global warming.   Root-nodule bacteria (Rhizobium) of this tree fix nitrogen used by this species and others in a forest (Walker 1990, 208).   Leaf, root, and stem feeders (parasites) include 2 aphid spp., 1 bacterium sp., 3 beetle spp., 7 borer spp. (including the Black Locust Borer), 2 bug spp., 1 butterfly sp. (Silver-Spotted Skipper), 2 dodder spp., 1 fly sp., 29 fungus spp., 1 beetle leafminer sp., 1 mistletoe sp., 2 mite spp., 7 moth spp., 1 phytoplasma, 1 sawfly sp., 12 scale spp., 3 treehopper sp., 1 virus kind, 1 walkingstick sp., (Horst 1990, 711; Westcott 1973, 561).   A phytoplasma in the Peach X Group causes witches’-brooms in Black Locust, especially in trees traumatized by topping (Chapman et al. 2000).

      Fomes rimosus, a rot-causing fungus, enters through borer wounds and causes decay in living trees (Walker 1990, 215).

      Nectar and pollen feeders (parasites, pollinators, predators) include many kinds of arthropods that consume their nectar, pollen, or both; they include butterfly spp., the Large Carpenter Bee, other bee spp.   This is a minor to major honey plant in the continental U.S. (Pellett 1978).   Honey Bees make a heavy, mild, watery-white honey from Black Locust.

      Bagworms, borers, fungus, Locust Leaf Miners, the Black Locust Borer (Megacylene robiniae), etc. parasitize this tree and can severely damage planted groves.   The Locust Leaf Miner causes premature browning and death of foliage.   In late summer, especially during dry summers, you can see 1000s of browned trees in the WDC Area.

      The Black Locust Borer damages and weakens trunks and limbs and is a possibly a black-and-yellow mimic of yellowjackets.   This Borer tends to enter tree trunks just as they approach fence-post size (Walker 1990, 215).   This Borer spoils the wood for most uses (except fence posts), and has reduced Black Locust's popularity for landscaping (Farrar 1995).   The moth Paraectopa robinella mines Black Locust leaves as larvae, sometimes causing much damage (Walker 1990, 215).

      Larvae of the Silver-spotted Skipper (butterfly) consume Black Locust leaves (Walker 1990, 215).   Please see Kudzu Vine for more information on this Skipper.   Longhorn beetles are important pests in shale barrens.   The Cottontail Rabbit often eats Black Locust bark during the cold season. Bark and twigs are poisonous to livestock.

      Seed eaters include the Bobwhite Quail, Mourning Dove, other birds, and small mammals eat Black Locust seeds.

Human uses.   Some people eat Black Locust flowers cooked and raw.   Humans make outstanding fritters using its flowers (Peterson 1977, 184).   We grow Black Locust as an ornamental and shade tree and as a shelter-belt tree (in areas with precipitation as low as 12 inches per year), and use it for erosion control.   Black Locust escapes from planted areas and takes over fields (Walker 1990, 214).

      Foresters plant Black Locust on spoil banks which contain toxins from mining where few other trees species can grow (Walker 1990, 213; Farrar 1995, 217).   This species helps to re-vegetate this disabled land.   People use Black Locust in the Near East and Middle East to reforest dry, abused land.   It will grow well in soil with a pH as low as 4, but it's optimum pH is about 7.

      Black Locust groves grow well when sprayed with municipal waste water (Walker 1990, 214).   The soil under the trees serves as a filter for germ- and organic-laden effluent.   These groves can be used as living filters for human wastes.

Wood.   Xylem: brown to greenish yellow, close grained, heavy, strong, tough, very durable in contact with soil, very hard.   Phloem: very thin, pale yellow.

      We use the wood for bows (used by Native Americans), corner posts of houses in barns (early colonists in North America), dowels for holding planks together, fence posts, hubs of wagon wheels (formerly), insulator pins for power lines, mine props, pilings of freshwater docks, posts, pulleys in mills (formerly), railroad ties, ship building (especially in the past), ship masts (in Colonial Times), tree nails, etc. (Bell and Lindsey 1990, 82).   Black Locust wood swells and contracts very little with changes in its moisture content.   The Ship-mast Locust (a clone) is valuable for its tall, straight boles (Harlow and Harrar 1958, 442).   Roy Underhill (in The Woodwright's Companion) reported that Black Locust wood lasts 2 years longer than stone and twice as long as its post hole.

Comments.   Black Locust is a pioneer species in old fields and elsewhere where it grows very rapidly (Kritcher and Morrison 1988, 128).   After it is established, it can spread rapidly by root sprouts, forming clones as Trembling Aspens do.

      Borers, fungus, and leaf miners parasitize this tree. It is often short lived due to its diseases (Stephens 1969, 151).

      GU Campus near Yates is sweetly fragrant from Black Locust flowers in May.   Depending on wind direction, there can be a carpet of white flowers at the base of the road to the Observatory.

      Black Locust, like most legumes, improves soil due to the nitrogen-fixing bacteria (Rhizobium) in its root nodules. Its leaf litter is also nitrogen rich.   Black Locusts cannot grow without their Rhizobium (Walker 1990, 200).

      Black Locust contains lectins known as toxalbumins (robin and phasin) which may interfere with protein synthesis in human small intestines and the glycoside robitin (Foster and Caras 1994, 182).   Black Locust roots have a sweet, licorice-like flavor but are somewhat poisonous (Stephens 1969, 151).

      Livestock die from browsing the bark or young shoots which have a toxin.

      Children become ill from chewing on young shoots and eating inner bark and seeds (Foster and Caras 1994, 182).   Symptoms of Black Locust ingestion include appetite loss, coldness of arms and legs, bloody diarrhea, depression, vomiting, and weak pulse.   Black Locust has spines, up to 1.2 inch long, that sprout from each side of old bud scars and new leaves (Walker 1990, 212).   These are modified stipules which are soft in many species.

      Black Locust roots have a strong odor when severed.

      Black Locust’s inconsistencies: rugged trunk but dainty flowers; durable wood but wrecked by borers; armed with thorns, but inviting in its durability (Walker 1990, 215).

Lab exercise: Capture a Black Locust Borer from goldenrod in late summer and autumn.
Listen to it stridulate.
Why does it stridulate?
Wombie (GU Class of 1994) was surprised that he couldn't hear the stridulation in 1993 in the Fernow.
He might have lost some of his hearing in night clubs.

E.M.B. (2002)

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