Black Locust
Robinia pseudoacaciaFabaceae
Whole Plant
Flower
Fruit
Leaf
Whole PlantFlowerFruitLeaf
Stem
Stem
Photos (c) Cheryl Comeau Beaton unless otherwise noted

Synonyms:

  • False acacia, Yellow locust
  • Robinia pseudoacacia var. rectissima

The Plant:

  • A medium, deciduous tree, 40-50 feet tall with a narrow crown. Widest at top, with upright to irregular branching, and a long straight trunk.

The Leaves:

  • dark
  • blue-green
  • dull
  • alternate
  • pinnately compound
  • 7 to 19 elliptic leaflets
  • stems glabrous
  • thorns around some buds

The Stem:

  • dark gray
  • furrows of bark are interlaced
  • distinct rope-like ridges

The Flowers:

  • Creamy white, pea-like, five-petaled flowers fragrant and growing in hanging clusters. Blooms from late May to early June.

The Fruits:

  • long flat pod
  • 2-4 inches long
  • October
  • persists
  • dried brown

The Habitat:

  • full sun
  • tolerant of dry, sandy conditions
  • salt, heat and pollution tolerant
  • fixes nitrogen

Dispersal:

  • mechanically dispersed seeds
  • spreads vegetatively by root suckers

Key ID Features:

  • medium sized deciduous tree
  • dark
  • blue-green
  • 7-19 leaflets
  • some thorns around buds
  • dark gray bark
  • rope-like ridges
  • long flat pods

Similar Species:

  • Honey locust (Gleditsia triacanthos) has pinnate leaves (like Black Locust) or it may have bipinnate leaves. It also has much larger spines, smaller, yellow-green flowers and long twisted pods, while Black locust has straight pods.
  • Two other locusts that also have invasive tendencies are Clammy locust (R. viscosa), which has sticky, gland-covered stems and pale pink flowers, and Hairy locust (R. hispida), which has hairy stems, egg-shaped leaflets, and rose-purple flowers.

Notes:

  • Seedlings and sprouts have distinct paired thorns and grow very rapidly. Shading out other plants Locusts kill off sun-loving native plants. Also its fragrant blooms draw the pollinating bees away from other native species. Due to its erosion control properties, nitrogen fixing abilities, and use in the lumber industry, Black Locust was widely planted and encouraged. its seeds generally don't germinate, therefore it creates clonal populations through root suckering and sprouting stumps all connected by the root system.
  • While this species is considered native in Pennsylvania and Virginia, it is not native to New England.
  • On Nantucket, this species tends to grow in small clusters of trees. Found on roadsides.

Growth Form: Tree

Origin: Southeastern United States, North Central United States, Lower Northeastern United States

Level of Invasiveness for Nantucket: Likely Invasive

Level of Invasiveness for Massachusetts: Invasive

Massachusetts Cultivation Restrictions: importation ban, propagation ban




Credits: The Electronic Field Guide to the Invasive Plants of Nantucket (c) 2005-2006 Maria Mitchell Association, EFG Project, UMass Boston