Tuesday, August 30, 2011

The Plant Behind the Monarch

Ever wonder what holds Kingdoms together? Often enough it's a plant.

Take for instance, the Monarch, Danaus plexippus, perhaps the best known of all North American butterflies, if you truly want to understand it you need to know about the plant genus Asclepias, that supports it. People love Monarch Butterflies but few know of the one plant that the pupa of monarchs, caterpillars, require to survive; Asclepias, commonly known as Butterfly Weed or Milkweed.

The reason Monarchs are so keen on this genus of plant is because of the chemical it contains; cardiac glycosides. As the monarch caterpillars eat the milkweed leaves they store the cardiac glycosides in their exoskeleton, making themselves toxic to predators such as birds. So birds in search of a meal quickly learn that the monarch is a unpalatable food that can make them vomit.

Few gardeners grow Asclepias, few landscape architects spec it in their designs, and few nurseries sell it, and yet it is crucial to the survival of this much loved wandering butterfly.

Friends of mine recently bought cut flowers of Ascelpias tuberosa, with showy orange blossoms, at the Green Market only to find a luminous green sac hanging from one of the stems. A week later a monarch butterfly shimmied out, though it didn't survive. Nonetheless, it was an inspiring process which they witnessed in their own Brooklyn apartment. Here are the pictures they sent.

I've often bought Asclepias tuberosa, only to realize the plant is hosting several caterpillars. What a wonderful gift to give to a garden, a rooftop, and to nature, more monarchs! And a plant they can return to every year to lay their eggs and feed upon as well as enjoy the nectar of the milkweed blossoms. Asclepias is also a diverse and beautiful genus with many species worthy of being in a garden.

Asclepias tuberosa is a late summer bloomer that is extremely drought tolerant, making it perfect for lazy gardeners or gardens with sandy dry soil. Here is it in one of our terrace projects combined with Yucca filamentosa.

Other Asclepias prefer more water, like the showy A. incarnata, which can get quite tall, and can be found by lakes or swamps. Here are a few pictures of it towering in my mothers garden.

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