Lathyrus tuberosus (Earthnut Pea)
|Also known as:||Tuberous Vetchling, Tuberous Pea, Earth Chestnut, Earthnut Peavine, Tuberous Sweetpea|
|Habitat:||part shade, sun; disturbed soil; roadsides, railroads, fields, woodland edges, waste places|
|Bloom season:||June - July|
|Plant height:||1 to 4 foot vine|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Clusters of 2 to 7 stalked flowers on stems arising from the leaf axils. Flowers are ½ to about ¾ inch (up to ~20 mm) long, pea-shaped, the upper petal (banner) broad and erect, forming a semi-circle over the smaller lateral petals (wings). Flower color is deep pink to purplish to red, the banner and wings usually the same shade but the banner often has a pale spot at the base.
The calyx holding the flower is bell-shaped, about ¼ inch long with 5 triangular teeth, the 2 upper teeth somewhat shorter than the 3 lower. The flower stalk is shorter than the flower and has a thread-like bract at the base. All parts are hairless.
Leaves and stems:
Leaves are compound with a single pair of leaflets at the tip of a short stalk. Leaflets are up to about 1½ inches long, blue-green, toothless, hairless, broadest at or above the middle, tapering at the base, the tip broadly pointed or rounded with a minute, sharp point at the apex (mucronate). Arising between the leaflets is a branched tendril. At the base of the leaf stalk is a pair of leafy appendages (stipules), up to about ¾ inch long with 2 lobes that are narrowly lance-elliptic and pointed at the tip, the lower lobe less than a quarter as long as the upper. Stems are branched, 4-sided with a ridge along 2 opposite angles, hairless, and sprawling or climbing, the tendrils winding around surrounding vegetation for support.
Earthnut Pea is not common in Minnesota, nor apparently very widespread in North America. It is distinguished by the underground tubers, blue-green foliage, 4-sided stems without wings, leaves with a single pair of leaflets and a tendril between the leaflets, leaflets mostly widest above the middle and often rounded at the tip. The broad banner petals resemble those of one of the Strophostyles species but the horn-like projections of those species are absent from Earthnut Pea. While there are other Lathyrus species (i.e. Everlasting Pea) that have leaves with a single pair of leaflets and a branched tendril, their stems and leaf stalks are broadly winged and leaves are larger, broadest at or below the middle.
Our thanks go out to Sherman in Duluth for alerting us to populations there.
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Have you seen this plant in Minnesota, or have any other comments about it?