Asclepias subulata – Growing With Science Blog

Some plants and pollinators have unique relationships. Take the rush milkweed.

Most years our rush milkweed plants only produce one or two seed pods each.

This year, however, the plants are covered with seed pods.

Why?

To figure out, we need to go back a few weeks. At that time the plants were covered with flowers.

We also saw a lot of tarantula hawk wasps visiting the flowers.

Although they are clumsy giants, tarantula hawks are especially good at pollinating milkweeds.Â Their long legs slide into the grooves in the flowers, where they collect the sticky sacs of pollen called pollinia (for more information, see BugGuide). When the wasps visit the next flower, the process is reversed, leaving the pollinia behind to pollinate the plant.

This year the tarantula hawk wasps were abundant and now the seed pods are, too, which hopefully means

soon we’ll see more milkweed seeds,

which will glide away on their silky parachutes to make more rush milkweed plants, which are

good for the monarch caterpillars that eat them, and

which turn into monarch butterflies, important pollinators for many other wildflowers.

All thanks to tarantula hawks!

As Tommy and Karen guessed last week, our mystery seeds from last week were from a milkweed. In particular, they are from the rush or leafless milkweed, Asclepias subulata.

Milkweeds come in a number of sizes and shapes. You may be familiar with the broad-leaved milkweed that grows in fields and on roadsides throughout North America:Â Asclepias syriaca, the common milkweed.

Common Milkweed

The rush or leafless milkweed that grows here in the Southwest lacks the large leaves.

Much of the year it looks like a clump of grey-green sticks, as shown in the left foreground of this photograph.

The flower structure, pods and seeds of the rush milkweed are similar to its relatives.

The rush milkweeds’ flowers are yellow, however, rather than pink.

As with all milkweeds, the flowers consist of a crown or corona, with five nectar cups. Many different insects visit the plant for the nectar in these cups, including: