Upcoming field expedition for triple ribbed milkvetch

Astragalus tricarinatus on a cliff face near Mission Creek 

This coming spring the Conservation Program has an exciting new project that will be undertaken in some remote and underexplored sections of our California deserts to look for a federally endangered plant called Astragalus tricarinatus, or triple ribbed milkvetch as its known by its common name. This plant grows on an unusual geological substrate called “distressed granite” that is formed along the San Andreas Fault line where it bends and twists from its north/south trending direction to a more east to west trending direction in the Coachella Valley area. This Astragalus is a California endemic which means it is found nowhere else and is also considered a narrow endemic as its found in a relatively small area.

"distressed granite" outcroppings along the Pacific Coast Trail

The Conservation program had the great opportunity in the spring of 2011 to do surveys for Astragalus tricarinatus in the Whitewater and Mission Creek area where we visited many historic locations, found new undocumented populations, and collected a great deal of habitat information for this unusual plant, however a number of questions where left unanswered concerning some very old collections and literary references to this species being in other areas much more to the east. One of these curios historic records was left by a plant taxonomist named R. C. Barneby who was the leading expert on this genus in the 20th century. In his notes on Astragalus tricarinatus he wrote that it occurs in the Orocopia Mountains in Riverside County. While the Orocopia Mountains are geologically quite diverse, and in the path of the San Andreas Fault, they are still around 40 miles further east than the general area where Astragalus tricarinatus is found. There was no physical specimen of A. tricarinatus that we could locate from this range so all we have is Barnaby’s word that it grows there. While Barneby’s expert knowledge holds a lot of weight it is also important to have a physical specimen in a herbarium that can be visited and studied and this is one of the main goals for this project we will be undertaking, to locate A. tricarinatus in the Orocopias, asses population status and population numbers and collect as much information on this endangered plant that we possibly can.

Spencer's voucher from Chuckwalla Mtns (Harvard image)

One herbarium specimen we do have to go on, that has also been one of question, is a collection from 1921 from Mary Spencer that was apparently collected even further east in the Chuckwalla Mountains. The Chuckwalla Mountains are pretty far from the San Andreas Fault, and while they are made up of granite they don’t appear to have the “distressed granite” that Astragalus tricarinatus prefers. So this specimen brings up many more questions: can A . tricarinatus grow on other geological substrates besides “distressed granite”? There has been a good deal of visitation by botanists to this range in the past 100 years, so is it possible that at one time A. tricarinatus did occur here but no longer does? Was this perhaps a “waif” population? And while Mary Spencer wrote on her collection label “Chuckwalla Mountains” could she have been referring to a larger area that would also include the Orocopia Mountains? The only thing we know for sure right now is that the plant collected by Mary Spencer is definitely A. tricarinatus, we have this very important herbarium record that we can visit and reference, but the big question is: where exactly did she collect it? Perhaps she found the same population that R. C. Barnaby writes of. These are all questions we are hoping to answer this coming spring.