A genetic analysis of a rare Arizona cactus: Echinocereus triglochidiatus var. arizonicus

Echinocereus triglochidiatus var. arizonicus is a federally endangered plant occurring in central Arizona. Since its 1979 listing, some botanists have questioned the definition of this taxon and its presumably limited range. Similar plants occurring in southeastern Arizona, classified by Benson (1982) as E. t. var. neomexicanus, are claimed to belong to the same taxon. RAPD analysis of plants from E. t. var. arizonicus, var. neomexicanus and the well-defined E. t. var. triglochidiatus were compared to determine genetic distance within and among groups. Genetic variability within groups was high and average genetic distance between groups nearly equal. Average heterozygosity levels within groups were not statistically different. RFLP analysis of noncoding chloroplast regions reveals a pattern of restriction sites and fragment lengths in three var. neomexicanus plants not present in plants of the other two taxa. The nature of the change was not determined but is consistent with a rearrangement of the region in question