Summer Botany: Meet the Milkweeds

Strolling the neighborhood on a cool July morning, in search of any newly-blooming botanical delights (thanks to our all-too-brief bout of monsoonal rains), from a distance I recognized something different. From a distance it looked like a common pepper plant, or maybe a spectacle pod? Coming closer I thought, “shepherd’s purse” with those tiny satchel-like seeds!  Or could it be bedstraw, with such an intoxicating fragrance?  Finally facing this spindly, narrow-leafed plant, I reached down to a stem and prepared to take a sniff when I was surprised twice!

An ant that had been busy gathering nectar (?) had leaped into my hand and bit me, hard! Obviously he was extremely upset at being disturbed and wanted me to know about it. I instantly dropped the stem and when I flicked the ant from my now throbbing finger, noticed an army of busy ants climbing up and down this tasty plant.

It was then that my surprise was complete. The flowers were unmistakable and recognizable.  This plant was a member of the Dogbane family ….. a beautiful Milkweed! Now I had to learn which species of Asclepias this one was that had such tiny flowers?

This new-to-me milkweed turns out to be Horsetail Milkweed, Asclepias subverticillata (subverticillata means “almost whorled” and refers to the leaf arrangement). This pretty milkweed is a common plant found along roadside habitats throughout the desert southwest. Although the narrow-leaved stems of my plants were less than 18” tall, there are reports of plants growing to 40”.  Wow. As with all milkweed species, this one is a suitable host plant for Monarch caterpillars.  I wonder if the taller ones are more easily seen by the adults as they flit around looking for a place to lay eggs? Maybe I should water my small population?

While pondering thoughts about butterflies, caterpillars and other pollinators, I began studying the exotic flowers of this milkweed. Such a highly evolved flower, with not just a calyx of 5 sepals and corolla of 5 reflexed petals, but a crowning Corona consisting of weirdly fused stamens and pistils. So many beautifully strange parts. Surely these plants require extra savvy pollinators to help the milkweed go from flower to fruit (aka follicle ….. when mature release those lovely gossamer silk-tethered seeds on a windy day).

I hastily gathered a few more facts and observations about this Horsetail Milkweed, because my curiosity was rapidly taking me down one of my fascinating rabbit trails.  Time to Geek Out big time!  I couldn’t resist learning more about the fascinating milkweed flower structures and just what clever insects have figured out the secrets to their successful pollination. 

So down the trail I ran, delving into the peculiarities of the complex flowers, “dissecting” all of their parts and mechanisms, and learning how they function in manipulating insects to carry those waxy masses of pollen from one plant to another. During this odyssey of discovery, I learned just how important this Asclepias genus is to the survival of Monarch butterflies … as the only host plants for their caterpillars, as an important nectar source for adults, and for their dependence on strong insect pollinators to fertilize the flowers and ensure future populations of milkweeds continue to grow across the butterfly’s range.

As with all of my rabbit trail adventures, this was educational, eye-opening and exceptionally fun.  The research that’s been conducted on the Asclepias genus seemed never ending (even though I couldn’t learn the purpose the corona’s horn serves).  It’s so important to understand how critical the connections are between different species for their survival, and how environmental impacts such as climate change and pesticide use can crumble an already teetering house of cards.

Your turn! Take a walk outside today and be amazed by something new!