The taxonomy of the genus Physaria (Brassicaceae) has been continually under revision as many species groups have proved difficult to resolve. Physaria intermedia (S. Watson) O'Kane Al-Shehbaz, has been a species whose circumscription has more recently been questioned and in need of clarification. The uncertainty surrounding the species stemmed from a combination of its geographical distribution, inhabiting two disjunct locations, as well as some minor differences in morphology that warranted a closer look. The species had been described as occupying southern Utah, northern and eastern (in northern 2/3) Arizona and southwest New Mexico with the remaining specimens inhabiting an isolated location in north-central New Mexico. Several P. intermedia specimens were analyzed molecularly and then morphologically to determine if any revisions to the taxon were needed. Maximum likelihood phylogenetic trees were constructed using three different gene regions from the extracted DNA of the specimens: the nuclear ribosomal ITS region, a 900 base-pair intron in the chloroplast rps 16 gene, and the 725 base-pair inteFgenic spacer between the chloroplast trnV and ndhC genes. The maximum likelihood trees provided strongly suggested an answer to what was going on in the P. intermedia species and gave two conclusions. The first conclusion from the molecular analysis determined that two previously named P. intermedia specimens had been mis-identified and actually belonged within two other Physaria species and were re-named to reflect the species they represented. The second conclusion found two separate and monophyletic groups within the remaining P. intermedia specimens, indicating the discovery of an unnamed Physaria species, and the species was ultimately split into two. The group of specimens inhabiting north-central New Mexico was determined to represent the actual P. intermedia species leaving those segregate specimens unnamed. The unnamed species of southern Utah, Arizona and southwest New Mexico will be given the name Physariafallax K.A. Arp & O'Kane.
Katie Arp (Sun,) studied this question.