Asclepias viridis (Green Milkweed) A small plant with small green flowers whose petals are pressed tight to the central column and with the horns hidden (or not present, I'm not sure which. I have never dissected a flower of this uncommon species). . Found in dry, sunny habitats like Serpentine Barrens.
Asclepias verticillata (Whorled milkweed) an inconspicuous plant with whorls of threadlike leaves and tiny white flowers in small umbels. The flowers have spreading hoods and projecting horns. Also found in dry, sunny habitats like Serpentine and Limestone Barrens.
Asclepias incarnata (Swamp milkweed) In full bloom right now, this common species lovely pink flowers and it is often seen in damp meadows and roadside ditches. The two-toned pink flowers are not as large as common milkweed but each plants has a lot of flowers.
Asclepias exaltata (Poke milkweed) White flowers in loose, drooping umbels with prominent projecting horns. There are relatively few flowers in each umbel but the flower stalks are very long. This species is an early bloomer (June here in PA and WV) which grows in sunny openings in deciduous forests.