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Black Locust

Robinia pseudoacacia

Summary 6

Robinia pseudoacacia, commonly known in its native territory as black locust, is a medium-sized hardwood deciduous tree, belonging to the tribe Robinieae of the legume family Fabaceae. It is native to a few small areas of the United States, but it has been widely planted and naturalized elsewhere in temperate North America, Europe, Southern Africa and Asia and is considered an invasive species in some areas, such as the temperate east coast of Australia where the cultivar 'Frisia'(Golden Robinia) was widely planted as a street tree before being classed as a weed. Another common name is false acacia, a literal translation of the specific name (pseudo meaning fake or false and acacia referring to the genus of plants with the same name).

Short Description 7

A fast-growing tree that grows 12 to 30 m (40-100 ft) high with compound leaves. Leaves have 7 to 21 oval leaflets-dark green on top and light green beneath. The flowers bloom between May and June-white flowers that hang in elongated clusters. Seedpods appear in fall and persist over winter; pods are smooth, dark brown, flat, and contain 4 to 8 flat, brown seeds.

Source: EwA Invasive Pocket Fieldguide | © Earthwise Aware

Description 6

Black locust reaches a typical height of 12–30 metres (40–100 feet) with a diameter of 0.61–1.22 m (2–4 ft). It is a very upright tree with a straight trunk and narrow crown that grows scraggly with age. The dark blue-green compound leaves with a contrasting lighter underside give this tree a beautiful appearance in the wind and contribute to its grace.

Black locust is a shade-intolerant species and therefore is typical of young woodlands and disturbed areas where sunlight is plentiful and the soil is dry. In this sense, black locust can be considered a weed tree. It also spreads by underground shoots or suckers, which contributes to the weedy character of this species. Young trees are often spiny, but mature trees often lack spines. In the early summer black locust flowers; the flowers are large and appear in large, intensely fragrant clusters reminiscent of orange blossoms. The leaflets fold together in wet weather and at night (nyctinasty), as some change of position at night is a habit of the entire leguminous family.

Although similar in general appearance to the honey locust, the black locust lacks that tree's characteristic long branched thorns on the trunk, having instead pairs of short prickles at the base of each leaf; the leaflets are also much broader than honey locust. It may resemble Styphnolobium japonicum, which has smaller flower spikes and lacks spines.

Black locust reproduces both sexually via flowers, and asexually via root suckers. The flowers are pollinated by insects, primarily by Hymenopteran insects. The physical construction of the flower separates the male and female parts so that self-pollination will not typically occur. The seedlings grow rapidly but they have a thick seed coat which means that not all seeds will germinate. The seed coat can be weakened via hot water, sulfuric acid, or be mechanically scarified, which will allow a greater quantity of the seeds to grow. The seeds are produced in good crops every year or every other year.

Root suckers are an important method of local reproduction of this tree. The roots may grow suckers after damage (by being hit with a lawn mower or otherwise damaged) or after no damage at all. The suckers are stems which grow from the roots, directly into the air and may grow into full trees. The main trunk also has the capability to grow sprouts and will do so after being cut down. This makes removal of black locust difficult as the suckers need to be continually removed from both the trunk and roots or the tree will regrow. This is considered an asexual form of reproduction.

The suckers allow black locust to grow into colonies which often exclude other species. These colonies may form dense thickets which shade out competition.
Black locust has been found to have either 2n=20 or 2n=22 chromosomes.

Black locust leaves contain flavone glycosides characterised by spectroscopic and chemical methods as the 7-O-β-ᴅ-glucuronopyranosyl-(1→2)[α-ʟ-rhamnopyranosyl-(1→6)]-β-ᴅ-glucopyranosides of acacetin (5,7-dihydroxy-4′-methoxyflavone), apigenin (5,7,4′-trihydroxyflavone), diosmetin (5,7,3′-trihydroxy-4′-methoxyflavone) and luteolin (5,7,3′,4′-tetrahydroxyflavone).

Invasiveness 8

The black locust is native to the eastern United States, but the exact native range is not accurately known as the tree has been cultivated and is currently found across the continent, in all the lower 48 states, eastern Canada, and British Columbia. The native range is thought to be two separate populations, one centered about the Appalachian Mountains, from Pennsylvania to northern Georgia, and a second westward focused around the Ozark Plateau and Ouachita Mountains of Arkansas, Oklahoma and Missouri.

Black locust's current range has been expanded by humans distributing the tree for landscaping and now includes Pakistan, India, Australia, Canada, China, Europe, Northern and South Africa, temperate regions in Asia, New Zealand, Southern South America.

Black locust is an interesting example of how one plant species can be considered invasive even on the continent to which it is native. For example, within the western United States, New England region, northern California, and in the Midwest, black locust is considered an invasive species. In the prairie and savanna regions of the Midwest black locust can dominate and shade open habitats. These ecosystems have been decreasing in size, and black locust is contributing to this reduction; when black locust invades an area, it will convert the grassland ecosystem into a forested ecosystem where the grasses are displaced. Black locust has been listed as invasive in Connecticut, Wisconsin, and Michigan, and is prohibited in Massachusetts.

In Australia black locust has become naturalized within Victoria, New South Wales, South Australia and Western Australia. It is considered an environmental weed there. In South Africa, it is regarded as a weed because of its suckering habit. In Asia, many black locusts, called cihuai (zh:刺槐), yanghuai (foreign huai zh:洋槐, against native huai zh:国槐) or simply "acacias", were planted in Dalian, Liaoning, China, during its Russian and Japanese occupation, and are loved by the local people: there is Acacia Avenue (槐树大道) in downtown; the Acacia Flower Festival (槐花節) is celebrated every year in May; and acacia honey is collected in the suburbs by bee keepers.

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Sources and Credits

  1. (c) Daniel Onea, some rights reserved (CC BY-NC), uploaded by Daniel Onea, https://www.inaturalist.org/observations/26297002
  2. (c) Jennifer Clifford , some rights reserved (CC BY-NC), uploaded by Jennifer Clifford , https://www.inaturalist.org/observations/86562358
  3. (c) Daniel Onea, some rights reserved (CC BY-NC), uploaded by Daniel Onea, https://www.inaturalist.org/observations/26294052
  4. (c) Deana Tempest Thomas, some rights reserved (CC BY-NC), uploaded by Deana Tempest Thomas, https://www.inaturalist.org/observations/91949884
  5. (c) Claire O'Neill, some rights reserved (CC BY-NC), uploaded by Claire O'Neill, https://www.inaturalist.org/observations/69500010
  6. (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Robinia_pseudoacacia
  7. (c) Claire O'Neill, some rights reserved (CC BY-SA)
  8. Adapted by Claire O'Neill from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Robinia_pseudoacacia

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