Bird’s-foot Trefoil (Hosackia oblongifolia, H. pinnata, & H. gracilis)

H. oblongifolia, Park Creek Trail, Shasta-Lassen NF. 7/2023.

Relatives of the common garden pea, native and non-native Trefoils are abundant in the pacific northwest woods. The three native varieties we’ve seen are from the Hosackia genus:

the Meadow Bird’s Foot Trefoil (H. pinnata) – found in grasslands of the Willamette Valley and Eastern Columbia Gorge,
Seaside Bird’s Foot Trefoil (H. gracilis) – found at coastal Cape Perpetua,
and Streambank Bird’s Foot Trefoil (H. oblongifolia) – found in the southern Cascade and Sierra foothills.
(We’ve seen but don’t have a good picture yet of a 4th variety, the quite different H. crassifolia, Big Deervetch.)

The Meadow and Seaside bloom earlier (April-May) at lower elevations than the Streambank (June-July). The Seaside is distinguished by its pink lower petals, and the Streambank by the red markings on its upper petals.

: Meadow (H. pinnata), Graham Oaks Preserve, OR 6/2015.

: Seaside (H. gracilis), Cape Perpetua, OR 5/2015.

: Streambank (H. oblongifolia), Shasta-Trinity National Forest, CA 7/2023.

We thought for years that all plants that looked like this were non-native, and paid little attention to them. Come to find out there are now three different genera of Bird’s-foot trefoil/Deervetch, only one of which is non-native. All three are in the pea (legume) family and used to be in the Lotus genus before recent revisions in taxonomy.

The genus Hosackia has several native North American species, most of which are commonly called Bird’s-foot trefoil (one is called Deervetch), and four of which we’ve found in the PNW.
The genus Acmispon has over twenty species native to North America, many of which are called Bird’s-foot trefoil, some of which are called Deervetch, some Deerweed, others Spanish Clover, and broom.
Several species remain in the genus Lotus. Those found in North America and the PNW, are all non-native. L. corniculatus is an all yellow species we often see.

To complicate matters further, the common name ‘Bird’s-foot’ refers to a 4th pea-family relative, the Ornithopus genus native to Europe, which has curved seed pods that look like the talons of a bird (good picture at this British Kew Royal Botanic Gardens website).