Lathyrus spp.—Vetchling; wild pea; flat pea
FAMILY: Fabaceae (Leguminosae)—the Bean Family (see Crotalaria)
PHENOLOGY: The vetchlings flower in summer, generally June through September. A few species flower earlier.
DISTRIBUTION: The genus Lathyrus is represented by at least a half dozen species in Pennsylvania. The native taxa generally are found in a diversity of habitats: L. ochroleucus L, dry or moist soil, slopes and rocky banks; L japonicus Willd., gravelly shores; L. palustris L, shores, damp thickets, meadows; L. venosus Muhl., rich woods, thickets, and banks of streams. The introduced taxa (L. aphaca L., L. tuberosa, and L. Iatifolius L.) either escape from cultivation to roadsides, thickets, and wasteplaces or are grown for ornamental value.
PLANT CHARACTERISTICS: Our species of Lathyrus are characterized by plants that vine; stems: winged or angular; leavres: alternate, even-pinnate, terminating in tendrus; stamens: diadelphous; pods: fat, dehiscent legumes.
POISONOUS PARTS: Of primary concern is the pea-like seed of some species. The foliage will also produce symptoms.
SYMPTOMS: Even moderate amounts of Lathyrus seeds in the diet do not produce poisonings. The development of lathyrism is apparent after consumption of large quantities or an exclusive diet of seeds. Lathyrism is well documented in human history when war, poverty, or drought have altered the diet of the people in a region. Human symptoms include paralysis (with loss of bladder or bowel control); slow, weak pulse; muscle tremors; a posture of feet turned-in, toes down; sensory disturbances; convulsions; and death.
Horses probably are the animals most sensitive to the toxic principles. They display symptoms similar to those cited above and also hind leg paralysis, dyspnea, and roaring. In toxicity experiments in rats, L. Iatifolius produced nervous symptoms of hyperexcitability, convulsions, and death.
POISONOUS PRINCIPLES: Numerous compounds have been extracted from various species of Lathyrus. One compound, L-alpha, gamma-diaminobutyric acid, isolated from L. Iatifolius, produces the symptoms described in the rat experiments noted above.
CONFUSED TAXA: The vetchlings (Lathyrus), which resemble the vetches (Vicia), differ in having wing petals separate from keel petals, and a fattened style, bearded on the inner face.
SPECIES OF ANIMALS AFFECTED: Both humans and livestock have been poisoned by Lathyrus.
TREATMENT: (11a)(b); (26); a change of diet, thereby removing the toxic principles, can alter the progress of the poisoning.