Asclepias tuberosa interior

Butterfly Milkweed - Asclepias tuberosa interior
Middle Percha, Black Range New Mexico, USA
Mid-July 2015

Butterfly Milkweed, Asclepias tuberosa interior, is an insect attractor.  Butterflies, as the name indicates, are particularly attracted to this species.  In mid-July 2015, we found this specimen in the Middle Percha, west of Kingston in the Black Range.  At that time, it was a Metallic Green Bee (of the genus Agapostemon) which was being attracted.

As seen in the map to the right, this species is found in much of the United States and parts of Canada.  The subspecies, A. t. interior, which we find here is the disjunct western population shown on the map and in much of the rest of the area except the far southeast and mid-Atlantic.

The root of this species was used to treat lung inflammations in the past.  One of its common names is Pleurisy Root, for that reason.  Other common names include Butterflyweed, Orange Milkweed, and Chigger Flower (that sounds dastardly).  Unlike other milkweeds, this species does not have milky sap.

This subspecies (A. t. interior) was first described by Robert Everard Woodson in 1944.  (Annals of the Missouri Botanical Garden, Vol. 31, 1944, pp 363 - 370, “Notes on Some North American Asclepias”).  In that description, I found two points which were especially interesting to me. The first is that he was working from specimens collected years before and identified differently.  In fact, Woodson has this to say about the specimen used to describe the subspecies (p. 367):

Continuing with the first point, the specimen shown below is maintained by the Smithsonian Institution, National Museum of Natural History, Department of Botany, it was collected by Mearns as part of the Mexican Boundary Survey (see detail below) more than 50 years before the subspecies was described by Woodson.

As for the second point.  At page 369 in his original description, Woodson includes a discussion about how to treat clines (a new concept at that time) and particularly how to indicate those specimens which are on the clinal edge - that artificial point where someone decides to draw the line and distinguish between two subsets of plant/animal.  I have included his discussion below because it seems imminently logical.  

and Metallic Green Bee - Agapostemon sp. 


© Robert Barnes 2018