Butterfly Milkweed (Asclepias tuberosa) Synonyms: Butterflyweed | Pleurisy Root | Tuberroot Perennial with deep, tuberous roots. Flowers are large clusters, orange to reddish, blooms from mid-June to mid-July. Attracts butterflies. May be poisonous to livestock. Adapted to many parts of the US. Usually in dry open soils of prairies, roadsides and waste places, upland woods. Best in full sun, well-drained sandy or gravelly soils; will endure drought well.