Narrow-leaved Milkweed has narrow leaves  hence the name  and a wide native range.  It is a perennial with 3' tall stem and large (but narrow) five inch leaves  and a five inch or so flower cluster. It tends to go dormant in the winter and regenerate the next year. It is a ?must-have? for butterfly gardens. The alkaloids associated with this plant give the butterfly larvae that feed on it protection but if the butterfly has not evolved with the milkweed they have no tolerance for the particular alkaloid of the species. In general it is larval food plant for the Monarch butterfly. In our area  this plant is covered with monarch caterpillars during the summer. Asclepias fascicularis can tolerate coastal clays.