Over the past few years, there has been more and more information coming out on the decline of insect populations. Of particular interest, monarch butterflies (Danaus plexippus), known for their incredible migration of up to 3,000 miles (Monarch Butterfly Migration and Overwintering (fs.fed.us)). In general, a major reason of species declines is loss of habitat, and for monarchs a large portion of that is loss of its host plant, milkweed.
Plants of the genus (Asclepias) are called milkweeds and are named for their sticky, white, latex sap that you will quickly notice after cutting a stem or leaf. This sap contains a cardiac glycoside which can act as a toxin in high doses. This toxic effect can act to prevent predation and browsing on milkweed plants; however, some animals (such as the monarch caterpillars) actually feed off these plants and have the ability to store or sequester the glycosides without harming themselves. These stored toxins in turn make the caterpillar and butterflies toxic or at least very bad tasting to potential predators such as birds.
Although the relationship with monarchs and milkweed is fascinating, I think one of the most remarkable traits of milkweeds is their flowers. I have always been amazed by their beauty and structural intricacy. I have found a quote on a couple of websites that say the complex structure of milkweed flowers is second only to orchids. Now I cannot find a citation to this claim and I am not a floral morphologist, so I cannot really say anything about this, but they are pretty. They can also be very fragrant, and different species have different colorations, including white, green, purple, pink, orange, yellows and reds. Once pollinated these flowers then turn into elongated fruits or pods, containing seeds. Milkweed seeds are attached to silky, white filaments or hairs that get blown and moved by the wind.
In my yard I have started growing a few species native to the area.
Common Milkweed (Asclepias syriaca). This one has broad oval shaped leaves with clusters of flowers forming balls, light purplish in color. Having planted this one in my front yard, I now know why this plant has the name weed in it…..be careful where you plant these becase one you have it in your yard it will sprout everywhere. They spread with rhizomatous roots, new shoots pop up everywhere. This might be better planted in an area that you do not mind getting overgrown.
Butterfly milkweed (Asclepias tuberosa) has more slender leaves compared to the common milkweed, with bright orange flowers. Apparently, they contain less of the glycosides compared to other milkweed species and are thus not used as much by the monarch butterflies as a host plant to lay their eggs on; but they will still feed off the nectar. These do not spread as aggressively as the common milkweed.
Swamp Milkweed (Asclepias incarnata) as shown above, has bunches of pink to mauvish flowers (photo on left), however; some plants have white flowers (photo on right). This species does well in wet, dense soils like clay…which I have a lot of.
There are over 73 species in the United States with a huge diversity in flower coloration and well as habitat preferences. I think if I were a botanist this would be the group I would study.
An African milkweed species, note the large seed pods.
(Danaus chrysippus) The African Monarch (also known as the African Queen or Plain Tiger butterfly) found throughout Africa and parts of Asia.
It may come as a surprise or is not something you regularly think about, but milkweeds, though native to North America are also native to other parts of the world including Africa. This milkweed plant above is one I spotted on the side of the road when I traveled to Madagascar. I immediately knew it was a milkweed, because of the large seed pods that looked like… well milkweed seed pods I had seen back home. In fact there is a species of butterfly (Danaus chrysippus) related to the North American monarch butterflies that feed and lay eggs on this milkweed. During my visit to Madagascar I also came across this incredible insect, the rainbow locust ( genus Phymateus), their bright colors like that of the monarch…..Although in the photo here they are not feeding on milkweed but on another plant. Nevertheless they are known to feed off of milkweed and like monarch caterpillars store the toxins (Monarchs and Milkweed in Madagascar – Insects on Plants, Chemical Ecology, and Coevolution (cornell.edu)). Our guide mentioned that the plant they are feeding on in this photo is also extremely toxic.
Rainbow locusts also feed on milkweeds and other poisonous plants and sequester the toxins.
Now I have come across some websites that mention you can eat milkweed, and many of friends will cry foul and say but its toxic, you cannot eat it! And indeed it is toxic, but toxic effects on the body depends on the amount consumed. The concentration or amount of toxins in an individual plant depends on the age and species. Regardless, I would not recommend trying to eat some, personally I am plenty happy with my vegetable garden or what I find in the stores. Interestingly, the amount of toxins from a plant that gets consumed can also depend on how you prepare or cook the plant. In fact when I lived in West Africa there was a cheese (Wagasi) made by the Fulani (or Peul) herders and they used the latex sap of the plant Calotropis procera to help curdle the milk. I remember this plant having similar flowers and leaf shape as those of milkweed plants here in North America, and in fact this genus of plants belongs to the same group as the milkweed plants I have been discussing, Asclepiadea. I believe the boiling of the plant helps to remove the toxin before it is added to the milk. Check out this video on the making of this delicious cheese! Wagashi Cheese Production in Northern Benin - Bing video
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