Robinia pseudoacacia (Black Locust)

Plant Info
Also known as:
Genus:Robinia
Family:Fabaceae (Pea)
Life cycle:perennial woody
Origin:Ozarks and Appalachia
Status:
  • Invasive - ERADICATE!
Habitat:sun; upland forest edges and openings, urban plantings
Bloom season:June
Plant height:30 to 60 feet
Wetland Indicator Status:GP: UPL MW: FACU NCNE: FACU
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: irregular Cluster type: raceme

[photo of flowers] Showy, hanging racemes 2 to 5 inches long in leaf axils of 1-year-old branches, each with up to 30 white pea-like flowers. The flowers are fragrant, ¾ to 1 inch long, the upper petal (standard) erect and greenish yellow at the base, the lower petal (keel) hiding the 10 stamens and single slender, curved style. The calyx surrounding the base of the flower is tubular, about ¼ inch long, hairy, often reddish or brownish green with 5 triangular lobes that are shorter than the tube.

Leaves and stems: Leaf attachment: alternate Leaf type: compound

[scan of compound leaf] Leaves are alternate, once compound, 4 to 12 inches long with 7 to 23 leaflets. Leaflets are elliptic to narrowly egg-shaped, ¾ to 2¼ inches long, rounded or tapered at the base and blunt or rounded at the tip, sometimes with a small notch. Edges are toothless, the upper surface smooth or finely hairy, lower surface with short appressed hairs along major veins. Fall color is typically a dirty yellow.

[photo of twigs] Young shoots are green and hairy with numerous pale lenticels (pores), turning red-brown and smooth. A pair of spines, ½ to ¾ inch long, may persist at the leaf scars or drop off older twigs. Buds are embedded in old leaf scars.

[photo of trunk] Branches become increasingly darker gray to gray-brown, the bark on the trunk coarse and deeply furrowed with forking ridges. The trunk can reach 24 inches in diameter at breast height (dbh).

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a small, thin, flat pod 2 to 4 inches long, green turning reddish or purplish brown at maturity.

[photo of seeds] Pods contain up to 10 hard seeds, mottled brown and black and about 1/6 inch long.

Notes:

Native to the higher elevations of the southeastern US, Black Locust's fast growth rate, tolerance of harsh growing conditions and its tough, rot resistant lumber gave it a high value during early settlement. It is also quite a pretty tree and horticulturists, especially in Europe, have made numerous selections on form and leaf color. In the past two centuries, humans seemed to have planted it everywhere and it is now widely established throughout much of the US, Europe, China and southern Australia. Unfortunately it is not well behaved, spreading by seed and, once established, produces large colonies through root suckering. It can readily exclude native shade trees important to natural ecosystems and due to its root suckers, difficult to manage without resorting to toxic chemicals. Young trees and saplings may be mistaken for Prickly Ash (Zanthoxylum americanum), which has leaflets with pointed tips, at least a few prickles along leaf stalks, and buds that are clearly visible, where Black Locust leaflets are rounded, has no spines or prickles on leaf stalks, and buds are obscured in the leaf scars. Seedlings and new root suckers may also be confused with any number of other members of the Pea family with similar compound leaves, such as Veiny Pea (Lathyrus venosus) or False Indigo (Amorpha fruticosa), all of which would lack spines.

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More photos

Photos courtesy Peter M. Dziuk taken in Anoka, Hennepin, Houston, Ramsey and Winona counties.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Chad M - Ottertail county, Pelican Rapids
on: 2017-07-07 20:50:40

I have spotted it growing along the old railroad track bed on the S.W end of town.

Posted by: SVERRE - COTTAGE GROVE, WASHINGTON CO
on: 2018-05-02 13:21:14

I have a 5 acre parcel that was once pasture land. These have made a solid establishment on my land. They produce an extremely hard wood that is also very good firewood. The folklore is the Spanish once used it to make their ships. I harvest the larger ones for firewood & have been eradicating the smaller ones ASAP.

Posted by: Koskela - Becker County, Lake Melissa Public Access
on: 2018-07-26 11:40:30

Found some Black Locust growing just off the boat launch.

Posted by: Brian V - Minnetonka
on: 2019-06-01 23:37:22

Found a young up-and-coming stand in an unmanaged forest on the property, they appear to be relatively quickly reproducing due to root suckering. While this stand isn't blooming as of yet, I have noticed that mature trees produce a highly sweet smelling blossom that is very pleasant. Apparently honey from these trees' nectar is also prized.

Posted by: Kz - Highwood Hills neighborhood in St. Paul
on: 2019-09-12 14:58:49

Saw this seedling for the first time on my property. It's beautiful but I know better. Pulled it. Thank you for the information. Your site helps me make informed decisions.

Posted by: Todd - Burnsville
on: 2021-09-14 07:54:09

I have a dozen or so of these trying to get started in my native grass/flower shoreline restoration area and will need to use chemicals to kill them, they can't be pulled out and cutting them results in fast regrowth.

Posted by: gary - St. Louis County
on: 2022-08-03 15:13:19

A large colony of this species grows on some rock outcrops near 15th Ave. West in Duluth. It appears to have been sprayed a few years ago but whether that will be enough I don't know. The plants have been here since the 1980s at least.

Posted by: Jo Ann - Plymouth
on: 2022-08-21 09:55:08

My Seek app identified it along the path on the east side of Medicine Lake this am.

Posted by: Sharon - Champlin
on: 2023-02-28 21:21:30

There is one at the dog park in the small dog enclosure at Zachary Ln, Champlin

Posted by: John - Houston County
on: 2023-09-06 20:29:59

How or Why is this plant an Invasive Native? I always save the seeds of this native plant to sow everywhere I go. Flowers Taste Great, Wood Quality is Good, Grows on extremely poor soils and builds those exact poor soils so more Natives can come in and thrive. Not to Mention Thorns keep deer away from other vulnerable Native Plants. Why would a Native Tree that Supports other Native species be labeled as Invasive to eradicate? Sure it might be weedy but that's because it's a pioneer tree species, that's the role they play in Native Ecosystems. This Native tree is restoring the ecological Damage we done to our soils, why are we fighting it?

Posted by: K Chayka
on: 2023-09-07 08:38:08

John, if you look at the national distribution map you'll see black locust is native to the south and east of Minnesota and is introduced (i.e. not native) elsewhere in North America.

Posted by: John - Houston County
on: 2023-09-10 23:59:47

So despite it being native on the same continent, It's still not Native to Minnesota? If so who introduced it here to Minnesota? If it were Native Americans who did, then does that mean it's still native? because of the prior to European settlement rule of how native plants are defined?

Posted by: K Chayka
on: 2023-09-11 12:44:35

John, per Welby Smith: "Black locust is native only in the Ozark and Appalachian regions of the eastern US, but it has been widely planted and naturalized beyond its original range. It was brought to MN in about 1860, possibly earlier, and was originally promoted for use in erosion control, as a windbreak, and for fuel, lumber and fence posts." It is unlikely Native Americans were responsible for its introduction here.

Posted by: John - Houston County
on: 2023-09-23 10:13:38

Interesting! Thank you for the info from Welby Smith! Is the Vice Versa also true for our state? In other words, would any Minnesota Native Plant, if it Extends beyond it's native range also be considered Invasive in other states? Just like how Black Locust is to us?

Posted by: K Chayka
on: 2023-09-23 16:57:20

John, assume any plant introduced outside its native range has the potential to become invasive there. It doesn't always happen, but could.

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