Thin-leaved pea – State Wildlife Action Plan

Thin-leaved pea is a perennial forb that is sparsely hairy to practically glabrous. The stems are strongly angled or narrowly winged and 30-100 cm long and have a climbing habit. The leaves are 6-10 cm long, alternate, compound and stipulate. The stipules are large and ovate to ovate-lanceolate with the margins coarsely undulate and the bases semi-sagittate. Leaves have 8-12 leaflets that are unpaired and ovate to lanceolate. Leaflets are 2-5 cm long, 0.7-3 cm broad, green above and paler below, glabrous, with welldeveloped tendrils. Inflorescences are 5-15 cm long racemes with peduncles that are often shorter than the leaves and mostly arranged on one side (secund). The white to cream flowers are 12-14(17) mm long, aging to light brown or orange. The calyx is 9-12 mm long with narrowly triangular lateral lobes. The flower banner pale greenish-cream with purplish-rose lines. The keel is approximately equal to the wings, if not slightly longer. Fruits are 3-5 cm long and 2-7 mm broad.

Overview

Species Common Name Thin-leaved pea
Species Scientific Name Lathyrus holochlorus
Federal Listing Status Species of Concern
State Listing Status Endangered

Ecoregions

Klamath Mountains

The Klamath Mountains ecoregion covers much of southwestern Oregon, including the Klamath Mountains, Siskiyou Mountains, the interior valleys and foothills between these and the Cascade Range, and the Rogue and Umpqua river valleys. Several popular and scenic rivers run through the ecoregion, including the Umpqua, Rogue, Illinois, and Applegate rivers. Historically, this ecoregion is known …

Willamette Valley

The Willamette Valley ecoregion is bounded on the west by the Coast Range and on the east by the Cascade Range. This long mostly level alluvial plain has some scattered areas of low basalt, and contrasts with productive farmland and large urban areas. It has the fastest-growing human population in the state resulting in challenges due to land-use changes.

Special needs

Thin-leaved pea habitat includes upland prairie, creek banks, forest edges, oak savannas, shrublands, and grasslands. Remnant habitat may also be found along roadsides and fencerows.

Limiting factors

Threatened by development and habitat conversion to agriculture. Plants in remnant habitats are at risk from human maintenance activities such as mowing and herbicide spraying. Encroachment of native species and non-native invasive plants may outcompete thin-leaved pea or alter habitat. The species is believed to be self-incompatible and an obligate outcrosser.

Data gaps

Assess genetic diversity and reproductive success of known populations. Develop propagation and transplanting protocols. Document population status and trends.

Conservation actions

Continue seed production efforts. Manage disturbance at known sites, especially along roadsides and fencerows. Monitor known populations. Remove invasives and encroaching shrubs and trees at sites using methods that minimize damage to thin-leaved pea plants. Identify suitable habitat on public land for introductions within the historic range of the species.

Key reference or plan

Marshall, DA, and J Brown. 2023. 2023 listing status assessment for Lathyrus holochlorus (thin-leaved pea). Oregon Department of Agriculture, Salem, Oregon.