Plant sources of omega-3s include flax seeds, hemp seeds, walnuts, walnut oil, soybeans, and purslane (Portulaca oleracea), a small green plant that most American gardeners consider a weed but whose leaves are viewed as a tasty addition to soups in Mediterranean countries and to salsa in Mexico.

A quarter-cup (1 ounce) of walnuts supplies about 2 grams of plant-based omega-3 fatty acids, slightly more than is found in 3 ounces of salmon.

The following website has two charts listing food sources of omega-3, including plant sources:

Foods sources of omega-3 fatty acids