26 June 2014

A Rare Treat

If you follow this blog, you know that I am a big fan of the milkweeds (Asclepias spp.), not only for their unique flower morphology but also for their importance to a long list of insect species.  It is no surprise, then, that on a recent trip to Starved Rock State Park near Utica in LaSalle County, Illinois, I had to stop to snap a few shots of the somewhat uncommon Poke Milkweed (Asclepias exaltata).


Unlike many of our milkweeds that grow in open to partly shaded conditions, Poke Milkweed thrives in rich soils and grows in partly shaded to shaded conditions of woodlands and forests.  Its range includes much of the eastern part of North America, extending west just past the Mississippi River into Minnesota and Iowa.


Although it isn't necessarily considered a species of conservation concern, when you are lucky enough to find Poke Milkweed, you generally don't see it in large numbers.  According to Swink and Wilhelm (1994), Poke Milkweed can be absent or found in very small numbers in a given forest for many years, and then inexplicably it will be found in great numbers in the same woods.


The flowers of Poke Milkweed are interesting in part because they are bi-colored.  The corolla lobes (petals) are greenish-yellow, whereas the hoods of the corona are white to faintly pink.


Although it has opposite leaves with milky sap, the leaves have a texture and venation that can superficially be confused with the alternate-leaved Pokeweed (Phytolacca americana), giving rise to the common name Poke Milkweed. This similarity was noted by Frederick Pursh, who assigned the Latin name Asclepias phytolaccoides to this species.  The older name Asclepias exaltata, assigned by Carl Linnaeus, is the currently accepted Latin name.

Swink, F. and G. Wilhelm. 1994. Plants of the Chicago Region. 4th edition. Indianapolis: Indiana Academy of Science.

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