Like little purple and white lights scattered amid a deep green tangle of leaves, the flowers of wild sweetpea illuminate many of the arroyos, gullies, and washes throughout the Preserve. This plant is known by a number of other common names including bush sweetpea, seemly sweetpea, bush vetchling, seemly vetchling, peavine, bush peavine, and purple peavine. Its scientific name is Lathyrus eucosmus. The genus name comes from the Greek word for pea or vetchling, lathyros. New Mexico is host to six native species in the genus Lathyrus, but to date I have only seen Lathyrus eucosmus growing on the Preserve. The species epithet comes from two Greek words; eu meaning good, well, or true and kosmos meaning order or ornament. Therefore wild sweetpea’s species name indicates it is a well- ornamented plant in the sense of being very beautiful, or seemly.
Wild sweetpea is a perennial sprawling vine growing from a taproot. Compound leaves arise in an alternate pattern from its smooth stems. Each compound leaf has six to ten narrow lance-shaped leaflets. The leaflets are leathery with conspicuous veins. The central axis of the compound leaf has leaflets on each side, but does not end in a leaflet. Instead of a leaflet, a tendril grows from the tip of the compound leaf. At the other end of the leaf, where it is attached to the stem, there are two small pointed leaf-like appendages called stipules.
The flowers of wild sweetpea bloom from May to September and arise in loose clusters of two to five blossoms. Each flower consists of an outer ring of five sepals fused into a bell-shaped structure with ten veins and five pointed lobes along the open edge of the bell. There are five petals that are structurally modified to create an overall floral shape distinctive to most members of the pea family. The broad conspicuous upper petal is purple to rose in color and bent backwards. It is often called the “banner” of the flower. The two smaller lateral petals are white and are referred to as the “wings.” The bottom two small purple/rose petals are fused to form the “keel” located between the wings. The fruit that develops from the central pistil of the flower is a small (less that two inches long), flat, strongly veined pod that turns a pale brown color as it matures.
The pea family, Fabaceae (formerly Leguminosae), is the third largest plant family worldwide after the aster and orchid families. It includes many common plants such as peas, clovers, vetches, beans, lupines, locoweeds, and also numerous woody species like mesquite, acacia, locust and redbud. With 45 genera and 239 native species, the pea family is also the third largest family in New Mexico after the aster and grass families. Fortunately, because of relatively obvious characteristics like their distinctive banner, wings, and keel flower structure, compound pinnate leaves, and fruit pods, most legumes are easy to recognize. The brightly colored flowers of wild sweetpea make the identification of this species especially straightforward. An infusion of Lathyrus eucosmus was used by Navajos to treat horses for various injuries or swellings. Even though I found no reference indicating wild sweetpea is edible, it nonetheless remains a valuable native plant in my book for its bright, cheery nature is sure to lift our spirits.
© 2011 Jerry Melaragno