This perennial wildflower is a vine about 1½-4' long that branches
occasionally. This vine climbs adjacent vegetation for support using
its tendrils. The stems are light green, yellowish green or reddish
green, glabrous or nearly so, and either winged, angular, or grooved.
Alternate compound leaves occur at intervals along these stems; they
are even-pinnate with 2-4 pairs of leaflets (usually there are 3 pairs
of leaflets). At the end of each compound leaf, there is a branched tendril.
The leaflets are ¾-2" long and 1/6-3/4" (4-20 mm.) wide; they are
narrowly elliptic to lanceolate-elliptic in shape and smooth along
their margins. The upper blade surface is medium green, while the lower
surface is pale green. All parts of the compound leaf are glabrous or
nearly so. The petioles and rachises of the compound leaves are light
green, yellowish green, or reddish green; they are glabrous or nearly
so. At the base of each petiole, there is a pair of stipules
¼-1" long. Each stipule is half-sagittate or half-hastate in shape; it
has a basal lobe that tapers to a point, a tip that tapers to a point, and an outer
margin that is usually smooth. Sometimes the foliage of this wildflower
is sparsely and minutely pubescent (puberulent).
Individual racemes of
2-8 flowers develop from the axils of compound leaves; the
peduncles of these racemes are about as long as, or a little shorter
than, the length of the compound leaves. Each flower is about ½-¾"
long, consisting of 5 petals with a pea-like floral structure, a
tubular calyx with 5 teeth, several stamens, and a pistil with a single
style. The petals consist of an upright banner and a pair of projecting
wings that enclose the keel. These petals can be pink, bluish purple,
or white; sometimes they are bicolored with a veiny
and white wings. The calyx is pale green or yellowish green and
glabrous. The blooming period occurs from late spring to mid-summer,
lasting about 1 month. Afterwards, the flowers are replaced by
elongated seedpods about 1-2½" long, ¼" across, and flattened.
Each seedpod splits open into two valves to release its seeds. The
small seeds are globoid in shape and somewhat flattened. The root
system is fibrous and rhizomatous. At favorable sites, vegetative
colonies of plants often develop from the rhizomes.
The preference is full or partial sun, wet to moist conditions, and
soil containing loam or sand. Standing water is tolerated if it is
occasional, rather than permanent. In the absence of some kind of
structural support, this vine will sprawl across the ground.
The native Marsh Pea is occasional in
of Illinois, while in the southern half of the state it is rare or
absent (see Distribution
). More broadly, it has a circumboreal
distribution, occurring in both North America and Eurasia. Habitats
include wet prairies, interdunal swales, borders of marshes, fens,
sedge meadows, low areas along streams, soggy thickets, and
swamps. This wildflower occurs in both sandy and non-sandy habitats.
The flowers attract primarily bumblebees and
long-tongued bees that feed mostly on nectar. Other insects feed on
foliage, flower tissues, or plant juices of Marsh Pea and other
These species include Acyrthosiphon
caterpillars of the butterflies Everes
(Eastern Tailed Blue)
and Leptotes marina
(Marine Blue), and Cerotoma
Beetle). In the past, the seeds of Lathyrus
were eaten by the
extinct Passenger Pigeon.
swale at the Indiana Dunes National Lakeshore in NW Indiana. The
photographed plant is Lathyrus
Marsh Pea is a variable species that has been divided into several
varieties, subspecies, or species in the past. As described by
Mohlenbrock (2008), the typical variety of Marsh Pea has winged stems
and narrow leaflets, while var.
has stems that are angular
and leaflets that are more broad. At one time, this latter variety was
even considered a distinct species, Lathyrus myrtifolius
& Brown, 1913/1970, Vol. 2). Today, most authorities no longer
recognize these varieties, subspecies, or species, lumping
all together under Lathyrus
. Regardless of its variations,
Marsh Pea can be distinguished from other Lathyrus spp.
the number of leaflets per compound leaf (typically 6), the
of flowers per raceme (2-8), and the shape of its individual
stipules (half-sagittate to half-hastate). For example, Lathyrus maritimus
(Beach Pea), which is found on beaches along
has individual stipules with a complete sagittate to hastate shape.
Another species, Lathyrus
(Veiny Pea), has more leaflets per
compound leaf and more flowers per raceme than Marsh Pea. In contrast
to the native species, non-native Lathyrus
within the state have
only 2 leaflets per compound leaf.