Acmispon americanus (American Bird's-foot Trefoil)

Plant Info
Also known as: Prairie Trefoil, Spanish Clover, American Deerweed
Genus:Acmispon
Family:Fabaceae (Pea)
Life cycle:annual
Origin:native
Habitat:sun; dry to moist sandy or rocky soil; prairies, shores, rock outcrops, along railroads
Bloom season:June - September
Plant height:6 to 20 inches
Wetland Indicator Status:GP: FACU 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

[photo of flowers] Flowers are single in the leaf axils along branching stems, up to ~1/3 inch (5 to 8 mm) long, white or pinkish. The broad upper petal (the standard) is erect and rounded at the tip, the lateral wings are smaller and more oval, extend outward and flank the yellow-tipped keel below. The calyx cupping the flower has 5 narrow lobes that may be longer than the flower; a leaf-like bract sits at its base. Flower stalks are longer or shorter than the subtending leaf. The calyx, bract and stalk are all covered in long spreading hairs.

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

[photo of leaves] Leaves are alternate, compound with 3 leaflets. Leaflets are up to ~1 inch (1 to 3 cm) long and to 3/8 inch (3 to 10 mm) wide, widest above, below or at the middle, toothless, hairy, pointed at the tip, tapering or rounded at the base, stalkless or nearly so.

[photo of stipules and hairy stem] At the base of the compound leaf is a pair of minute, gland-like stipules, commonly reddish brown. Stems are erect to spreading, freely branching, covered in long spreading hairs.

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a slender, straight, bean-like pod, about 1 inch (15 to 35 mm) long and containing up to 8 seeds.

Notes:

American Bird's-foot Trefoil, formerly Lotus purshianus (or Lotus unifoliolatus), is uncommon in Minnesota, found primarily in dry sandy prairies, rock outcrops, and along railroads, occasionally shores or wetter areas. It is a relatively short plant, rarely getting knee-high, and the many branches can give it a bushy appearance. It somewhat resembles the invasive Bird's-foot Trefoil (Lotus corniculatus), which has small clusters of yellow flowers, lacks the long, spreading hairs, and has large leaf-like stipules at the base of the leaf stalk.

There are 2 vars of Acmispon americanus, though some references consider them separate species; var. helleri, restricted to the Piedmont region of the southeastern US, is hairless or short-hairy and its leaflets are proportionately narrower (4 to 5x long as wide); var. americanus, present mostly west of the Mississippi River (considered introduced farther east), is long-hairy with broader leaflets (3 to 3.5x long as wide).

Native Plant Nurseries, Restoration and Landscaping Services ↓

Map of native plant resources in the upper midwest

  • Minnesota Native Landscapes - Your Ecological Problem Solvers
  • Spangle Creek Labs - Native orchids, lab propagated
  • Prairie Restorations - Bringing people together with the land
  • Landscape Alternatives
  • Out Back Nursery

More photos

Photos by K. Chayka taken in Ramsey County. Photos by Peter M. Dziuk taken in Chippewa County.

Comments

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

Posted by: Jessica - Pipestone National Monument, Pipestone, MN
on: 2015-07-01 21:47:17

Just found this one last week while working out at Pipestone National Monument. Lovely little surprise - at first I thought it might be a diminutive tick trefoil (Desmodium). If this page didn't have it, I was about to pour through the Great Plains flora to look for it. Thanks for the ID!

Posted by: Gabriel Miller - Goodhue Co.
on: 2022-07-29 16:36:03

Growing along periphery of UTV trails paralleling railway. apparently not supposed to be in this county. Many small plants, none over 8 inches. The tiny, singular white flowers lead me to believe this is the right ID.

Posted by: K Chayka
on: 2022-07-29 16:51:38

Gabriel, seeing it along trail edges leads me to believe it was brought in on a vehicle's tires.

Post a comment

Note: All comments are moderated before posting to keep the spammers out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.



(required)




Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because I’d like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.