The flowers of Asclepias macropus are born in a densely flowered, spherical, solitary umbel at a stem tip. There may occasionally be two umbels on one stem. The upper stem seen below the inflorescence is sturdy here, purplish green in colour. The leaves growing lower down on the stem, become sparsely spaced close to the flowers.

The five corolla lobes (or petals) of the flower are lined with purple and green, reflexed right back over its pedicel, although their tips again curve up. They are broadly ovate, tapering to acute tips. The upper, yellow (sometimes green) flower part, a conspicuous five-pointed star, is formed by the boat-shaped corona lobes around the central staminal column.

A single, curved follicle that contains the seeds arrives after the summer flowers (JSTOR).