Flat pea (Lathyrus sylvestris)

Synonyms: Lathyrus platyphyllos, Lathyrus angustifolius

Common Names: Flat peavine, everlasting pea, narrow-leaved vetchling, wood pea

Description:

Flat pea (Lathyrus sylvestris) is a scrambling, climbing perennial in the pea family, native to Europe and western Asia [1][3]. It was brought to North America and planted along roadsides and on disturbed land for erosion control and soil improvement, and has since escaped into fields, edges, and natural areas [2][3]. MISIN tracks it because it forms dense mats that climb over and smother other plants, and because its seeds contain compounds that are toxic if eaten [3].

Habit:

Flat pea is a long-lived, scrambling perennial vine that climbs to about 7 feet where it can grab onto something and sprawls into a dense mat about 2 to 3 feet high where it cannot [3]. Its most distinctive feature is its stems: they are flat and floppy, edged with wide, leaf-like "wings" that run down the stem [3]. It is easiest to identify in summer, when it produces elongated clusters of showy pinkish-red pea flowers [3]. Each leaf is made of a single pair of long, narrow leaflets with a branched tendril reaching out from between them, which the plant uses to climb [3].

At-a-glance cues:

1. Flat stems edged with wide, leaf-like wings [3]
2. Leaves of a single pair of long, narrow leaflets with a branched tendril at the tip [3]
3. Elongated clusters of pinkish-red pea flowers in summer [3]
4. Dense, scrambling mats along roadsides, field edges, and disturbed ground [3]

Leaves:

1. Arrangement: alternate along the stem [3]
2. Type: each leaf a single pair of leaflets, with a branched tendril at the tip [3]
3. Shape: leaflets long and narrow, with roughly parallel veins [3]
4. Color: green [3]

Stems:

1. Habit: herbaceous perennial, scrambling to climbing, forming dense mats [3]
2. Shape: flat and floppy, edged with wide, leaf-like wings [3]
3. Color: green [3]
4. Spread: creeps outward by rhizomes (underground stems) [3]

Flowers:

1. Color: pinkish-red to reddish [3]
2. Shape: pea-shaped, with five petals in an irregular arrangement [3]
3. Arrangement: elongated clusters of about 3 to 10 flowers [3]
4. Bloom time: summer [3]

Fruit and seeds:

1. Fruit type: a flattened pea pod, about 2 inches long [3]
2. Seeds: 5 to 15 dark seeds per pod [3]
3. Ripening: pods mature in summer [3]
4. Note: the seeds contain compounds that are toxic if eaten in quantity [3]

Habitat:

Flat pea is native to Europe and western Asia, from Great Britain east toward Siberia [3]. It is not native to North America, where it has been introduced and now grows from Canada through the northern United States and south to about Georgia [3]. It turns up in fields, along roadsides and railroads, in disturbed ground, and at forest edges and openings [2][3]. It tolerates poor, dry, acidic soils that many plants struggle in ? which is exactly why it was planted for erosion control and land reclamation, and part of why it persists and spreads once established [3].

Reproduction:

Flat pea spreads two ways. It produces seed in flattened pods, but those seeds mostly fall near the parent plant rather than traveling far on their own [3]. More important for its spread is that it creeps outward underground: it sends out rhizomes (underground stems) that let a single plant widen into a dense mat over time [3]. Like other members of the pea family, it also fixes nitrogen, which helps it thrive on poor soils [3]. Because it comes back from its rhizomes as well as from seed, the key to control is to remove the roots and cut or pull plants before the pods ripen, and to keep after any regrowth [3].

Impact and Damage:

For homeowners, the main concern with flat pea is that it is toxic. Its seeds contain a compound (diaminobutyric acid) that can be harmful if eaten in quantity, and large amounts can cause lathyrism, a disorder of the nervous system; it is also toxic to livestock that are not acclimated to it [3]. That makes it worth keeping out of pastures and hay and away from where children or pets might pick at the pods. It is otherwise a vigorous vine that can scramble over a garden or fence line and be hard to keep in bounds [3].

For natural area stewards, the concern is its habit of forming dense mats that climb over and smother other plants, which can prevent native plants from establishing where it spreads [3]. It was deliberately introduced for erosion control and soil improvement, but it escapes those plantings into surrounding fields and natural areas [2][3]. It is recognized as an invasive or weedy plant in parts of North America, though it is not a federally regulated noxious weed [2][4]. No quantitative figures for native-plant displacement or economic loss from this species were found in the sources reviewed.

Similar species:

Flat pea is easily confused with several other climbing or mat-forming legumes, especially when it is in flower.

Everlasting pea (Lathyrus latifolius) is its closest look-alike ? another winged-stemmed climbing perennial pea with pinkish flowers and climbing tendrils. The clearest difference is the leaflets: everlasting pea has broad, oblong to elliptic leaflets up to about 4 inches long, while flat pea's leaflets are distinctly long and narrow [3][4].

Crownvetch (Securigera varia) is another sprawling, mat-forming legume planted for erosion control, with pink-and-white pea flowers. It is told apart by its leaves, which are divided into 15 to 25 small leaflets rather than flat pea's single narrow pair, and by its rounded, head-like flower clusters and plain (unwinged) stems [5].

Vetches (Vicia species) are climbing legumes that also use tendrils, but their leaves are divided into many small leaflets, unlike flat pea's single pair of narrow leaflets, and their stems are not broadly winged [3].

Monitoring and rapid response:

Signs to watch for:

1. Dense, scrambling mats of vines with flat, winged stems along roadsides, field edges, and disturbed ground [3]
2. Elongated clusters of pinkish-red pea flowers in summer [3]
3. Patches spreading outward from old erosion-control or reclamation plantings [2][3]

What you can do:

1. Hand-pull or dig out plants while they are young, removing the rhizomes (underground stems) as well as the top growth, since the plant regrows from its roots [3]
2. Cut or mow plants before the pods ripen to stop seed from forming, and repeat through the season as the plant resprouts [3]
3. Bag and remove pods and seeds rather than composting them ? the seeds are toxic and can also start new plants [3]
4. Wear gloves when handling the plant, and keep the pods away from children, pets, and livestock [3]
5. Natural area crews should dig out small, outlying patches first, cut larger patches repeatedly to prevent seed set, and watch for plants spreading from old reclamation plantings [3]

When to call a professional:

1. Large, well-established mats that keep resprouting from rhizomes after cutting
2. Sites where digging out the roots by hand isn't practical across the whole patch
3. Roadside or right-of-way situations that need a coordinated, multi-year plan
4. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. GBIF Backbone Taxonomy. Lathyrus sylvestris L. gbif.org
2. USDA PLANTS Database. Lathyrus sylvestris L. (flatpea). plants.usda.gov
3. North Carolina State University Extension Gardener Plant Toolbox. Lathyrus sylvestris (Flat Pea, Everlasting Pea). plants.ces.ncsu.edu
4. Invasive Plant Atlas of the United States. Flat peavine: Lathyrus sylvestris. invasiveplantatlas.org
5. North Carolina State University Extension Gardener Plant Toolbox. Securigera varia (Crown Vetch). plants.ces.ncsu.edu

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