Black Locust Tree: Types And Pictures

The black locust tree, or Robinia pseudoacacia, is a deciduous tree found throughout the southeastern United States, as well as in South Africa, Europe, and Asia. The tree is native to the southeastern United States, but it has been transplanted to other areas of the globe such as Australia, Pakistan, China, Canada, India, Europe, South Africa, Asia, southern South America, and New Zealand.

The black locust tree is a deciduous tree of medium-size, and it is sometimes called false acacia. Various types or cultivars of the tree can be found in the US and around the world.

Physical Characteristics

Black Locust trees usually grow to between 12 to 30 meters high, or 40 to 100 feet high. They have a diameter of between 0.60 to 1.2 meters ( 2- 4 feet). Certain specimens have grown up to 1.6 m or 5.2 feet in diameter and 52 m or 171 feet tall. Black Locust trees have a narrow crown that tends to become bushy as the tree ages. The leaves of the tree are usually a dark bluish green with a lighter underside.

Black locust trees need plenty of sunlight to grow, not tolerating shade well. Black locusts are often thought of as weed trees, because they frequently grow in areas that have been disturbed or cleared, where sunlight is plentiful between gaps in other congregations of trees. Black locusts frequently spread through underground shoots as well. Frequently the trees have spines when they are young, losing the spines as they mature.

Photo: By Pollinator, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2040096

The flowers of the trees are very plentiful and they appear in large dense clusters on the tree. The flowers usually open for about a week and a half in May or June, and are fairly large, being between 10 to 20 cm (4 to 8 inches) in length. The flowers are known for their powerful fragrance. While the flowers are normally white, some varieties of black locust have purple or pink flowers. The flowers hang down from the branches of the tree and they often provide nectar for honeybees. In return, these honeybees pollinate the plant.

The bark of the tree is usually gray and black with a red or orange tinge to it. The bark has many ridges and grooves that frequently form diamond patterns along the trunk of the tree. Young trees often have a white downy substance that disappears as the tree matures. The wood of the tree is dense, hard, and durable, and it has a light yellow color to it. The tree produces a legume fruit which is between 5 to 10 cm or 2 to 4 inches long and about 1.3 cm or half an inch thick. The fruits usually have between 4 to 8 seeds in them.

During the winter the tree’s buds are naked and are clumped together in three or four units. The buds are located in a recession in the tree, which helps protect them from the cold until they open during the early spring.

History Of The Black Locust Tree

Robinia pseudoacacia is said to have been given the name locust by Jesuits who claim that the tree once supported St. John as he lived in the wilds, referencing a tree in the New Testament of the Bible. However, the black locust is native only to southeastern North America. The exact original/native range of the tree isn’t known, and it has spread across the United States and can now be found in the entire lower 48 states, as well as parts of British Columbia and Eastern Canada.

Humans have greatly expanded the range of the black locust. The tree had been transplanted to many different countries around the globe. Interestingly enough, the black locust is sometimes considered an invasive species even within the United States, particularly in the Western states and in New England. In these regions, black locust has come to dominate open habitats, frequently displacing natural grasses and the species that depend on them. Black locust has been formally listed as an invasive species in Wisconsin and Connecticut, and the state of Massachusetts prohibits it. The tree is also considered an invasive species in parts of Australia and South Africa.

Reproduction

Black Locust trees are capable of reproducing both sexually and asexually. They reproduce asexually using suckers and sexually with flowers that are pollinated by insects. Hymenoptera insects are the primary pollinators of black locust flowers. The physical characteristics of the flowers prevent the male and female parts from coming into contact, keeping self-pollination to a minimum. Black Locust seedlings can grow quite quickly, but because the seeds have a thick coat, not all of the seeds will end up germinating. Good crops of seeds can be harvested every year or every two years.

The extensive root sucker networks that black locust trees produce mean that tree is a very resilient species. The roots suckers grow out of the roots and into the air, and they can easily grow into full trees. In addition, the trunk of the tree can still grow sprouts even after being cut down. The suckers must be constantly and diligently removed from both the roots of the trees and of the trunk of the tree or else it will simply regrow. Because of its resilient nature, black locust trees can quickly create colonies that block out other species of trees, shading out competitors.

Human Uses

Black Locust trees are used as honey plants in the Eastern portion of the United States. European countries also use them as honey plants, and a type of honey called acacia honey is created with them. After 140 growing days, the black Locust tree flowers begin to bloom. The amount of honey that can be collected is limited because of the black locust flower’s rather short blooming period. The tree does not consistently produce a honey crop every year. Black locust trees in Ohio only produce a viable amount of honey once every five years or so. The volume of honey generated by the flowers is impacted by weather conditions.

Black Locust trees are frequently used as nitrogen-fixing trees. The nitrogen-fixing nodules on the roots of the plant can enrich the soil, and this attribute makes it a handy replacement for other forms of vegetation that cannot fix nitrogen, especially in sandy soils.

The wood of the locust tree is one of the hardest woods found on the North American continent. In addition, it is resistant to rot. These features make it popular choices for woodworking and the creation of fence posts, small boats, wooden paneling, flooring, and furniture. It is also frequently planted for firewood because it grows quite quickly. When the wood is newly cut, it has a foul odor but this odor disappears as the wood ages. The wood burns slowly and produces little smoke, which adds to its popularity as firewood.

Different portions of the black locust tree are used as diuretics, laxatives, and antispasmodics in India. In Romania, the flowers of the tree are frequently used to create a sweet jam. To create this jam the flowers must be picked, stripped of seeds, and the petals boiled in sugar. The leaves and bark of the tree of toxic, but it is possible that the pods and seeds of the tree are edible. Shelled seeds can be harvested from the beginning of the summer to the fall, and they can be eaten boiled or raw. There is some disagreement over whether or not the toxins in the tree can be nullified by cooking, with some claims that the tree is merely poisonous to humans.

Varieties/Cultivares Of Locust Trees

Various types of locust trees or cultivars exist. The different varieties of the tree have different primary purposes. Some varieties of the Locust tree are grown primarily for the collection of honey, while others are used for ornamental purposes because of their attractive foliage. The features of the different varieties will differ, and some varieties that don’t have seed pods or thorns. Some honey locust cultivars are used as landscape trees. Another way that varieties of black locust differ from one another is that the leaves of honey black locusts don’t have leaflets at their tip.

Photo: By © User:Colin / Wikimedia Commons, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16920751

Some of the more famous cultivars include Decaisneana, Frisia, Purple robe, Tortuosa, Unifoliola.

Decaisneana Is a hybrid of two different Robinia species, it is distinguished by its small forms and rose pink flowers. Frisia has bright red thorns/prickles and bright yellow-green leaves. It’s striking colors make it a popular ornamental tree. Tortuosa is a cultivar known for its curved and warped looking branches. Unifoliola is shorter than other varieties of locust tree, and it also possesses no spines. The purple robe tree gets its name from its purplish pink flowers. Like Frisia, purple robe has red prickles. The tree’s flowers often stay blooming for longer than other varieties of black locust.

About The Author

Daniel Nelson

Daniel obtained his BS and is pursuing a Master's degree in the science of Human-Computer Interaction. He hopes to work on projects which bridge the sciences and humanities. His background in education and training is diverse including education in computer science, communication theory, psychology, and philosophy. He aims to create content that educates, persuades, entertains and inspires.

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