August 11, 2020 Asclepias fascicularis Narrow-leaf Milkweed Monarch butterfly on narrow-leaf milkweed (Asclepias fascicularis). Photo by TJ Gehling, CC BY-NC-ND 2.0.Monarch caterpillar on Asclepias fascicularis. Photo by Jane Kelly. More InformationNarrow-Leaf Milkweed and Una, Dos, Tres—the Monarch TrioPartners Work to Help Monarch Butterflies by Expanding a Locally Scarce Milkweed Species