Gods & Monarchs

What’s the relationship between Asclepius and Asclepias? It isn’t all about words, or declension. There are real differences worth sorting through.

First we should check on Asclepius (also spelled Asclepios). In short, Asclepius was the mythological son of Apollo, inheriting and amplifying the family trade as gods of healing, indeed passing that tradition on to his own daughters Hygieia, Iaso, Aceso, Aegle, and Panacea. The family was sufficiently important in healthcare as to be invoked in preface to the Hippocratic Oath: “I swear by Apollo the Physician and by Asclepius and by Hygieia and Panacea and by all the gods …”

Like Harry Potter, Asclepius was associated with snakes and their power – his symbol a staff entwined with a single serpent. Adopted worldwide as a medical emblem (one snake wrapping around a staff), the symbol was upsized by the US military corps to feature two snakes, which makes their sign equivalent to a different staff, the caduceus, a symmetrical, 2-snake device that is the mark of Mercury (Hermes), messenger of the gods.

Leaving Asclepius aside, we move to Asclepias, a wonderful genus of plants in the Dogbane family, plants native to the New and Old Worlds. The name goes back over two thousand years, used by Dioscorides in reference to an herb he recognized as having medicinal value. But things went sideways by the 18th century, when Linnaeus and his contemporaries adopted this name for plants native to America. And even more sideways when we consider that the American plant first brought into the relationship bears the name Asclepias syriacus (suggesting it originated in Syria).

How do things like this happen? The simplest way to make sense of the situation is to go back to the year 1623. That’s when Caspar Bauhin published his Pinax theatre botanici, a remarkable concordance to the growing mountain of publications on plants (mostly herbals). Bauhin examined the many names different authors had applied to plants, and created this great index to that literature. Turning to page 303 in Pinax, we learn Bauhin records the plant Fuchs called Asclepias (with references to ancient herbal uses described by Pliny and Dioscorides) as equivalent to an herb recently discovered in Virginia.

Illustration of Asclepias from Fuchs, 1542 De historia stirpium commentarii insignes. Though this illustration is part of the basis for Bauhin’s concept of Asclepias, it has long been recognized as an Apocynum – leaving American and African plants as the plants we call Asclepias today.

Bauhin’s work was fundamental to Linnaeus’ ability to make sense out of the many differently-named plants that had been published since Gutenberg introduced printing to European scholarship. This was crucial because Linnaeus and his contemporaries were inundated with the growing trove of newly discovered plants from Asia, Africa, and America.

Linnaeus not only accepted Bauhin’s concordance, but moved ahead to describe many more plants as new species of Asclepius. Subsequent botanists pruned the genus down to include a clearly distinguishable group of plants, in the process tossing out the European and Mediterranean plants Fuchs and earlier herbalists had called Asclepias. Because plant nomenclature begins with Linnaeus’ 1753 Species Plantarum, and he began his treatment with Asclepias syriacus, the dye was cast; i.e. the genus Asclepias is based on A. syriacus as its type.

Asclepias tuberosa visited by Papilios in Missouri

Asclepias thus carries an adopted name with quietly obscure origins. But the plant itself is far from forgotten. Asclepias is well-known to North American botanists and gardeners for its wonderful associations with butterflies. The common Eastern US plant, Asclepias tuberosa, is called butterfly weed because the flowers can be seen loaded with Papilio butterflies. Its curious knobby flowers exemplify others in the genus, with their highly detailed floral structure that relates to persnickety pollination mechanisms.

But these plants are not simply sources of nectar; they share a much deeper relationship with butterflies as nurse plants for Monarch butterfly larvae. We grow Asclepias curassavica (a Central American species) at The Huntington as sites for Monarchs to lay their eggs, where larvae hatch and feed solely on the Asclepius foliage. At maturity, the caterpillars crawl away and pupate in other locations around the garden. People delight at the occasional encounter of a Monarch emerging from its chrysalis

Asclepias curassavica in the Huntington Herb Garden
A closer look at individual flowers of Asclepias curassavica.

Some References and Links….

Monarchs and Mildweed, A Migrating Butterfly, a Poisonous Plant, and their Remarkable Story of Coevolution. 2017. Anurag Agrawal, Princeton University Press.

Fishbein, Mark, David Chuba, Chris Ellison, Roberta J. Mason-Gamer, and Steven P. Lynch, 2011. “Phylogenetic Relationships of Asclepias (Apocynaceae) Inferred from Non-Coding Chloroplast DNA Sequences.” Systematic Botany, 36(4) : 1008-1023. https://doi.org/10.1600/036364411X605010

Pinax link

Asclepias syriacus https://link.springer.com/article/10.1007%2FBF02858278?LI=true

“The History and Use of Milkweed” https://link.springer.com/article/10.1007/BF02858278

Robert E. Woodson, 1954. “The North American Species of Asclepias L.”, Annals Missouri Bot Gard, 41:1-211 https://biodiversitylibrary.org/page/16156875

Insects on Plants, Chemical Ecology, and Coevolution

Website of the Phytophagy Lab at Cornell University, led by Anurag AgrawalJames A. Perkins Professor of Environmental Studies Milkweeds but not monarchs in Europe: natural and cultural history (and a modest proposal)

Leonard Fuchs, De historia stirpium commentaii insignes, 1542, https://library.si.edu/digital-library/book/dehistoriastirp00fuch

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