ISOZYME VARIATION IN ECHINOCEREUS-ENGELMANNII VAR MUNZII (CACTACEAE)

Assessing the degree of evolutionary differentiation between a rare ta xon and its relatives is critical from a biological perspective. Becau se funding and time are limited, conservation biologists need to set m aintenance of truly unique pieces of biodiversity as a higher priority than maintenance of interesting populations of widespread species. Al though many factors go into setting priorities, thorough assessment of evolutionary distinctiveness based on multiple lines of evidence is t he most basic. We used isozyme characters to assess the distinctivenes s of a purportedly rare taxon, Echinocereus engelmannii var. munzii (M unz's hedgehog cactus), from other common varieties of the same specie s. We sampled at least 15 individuals from one population in each of t he three mountain ranges where E. e. var. munzii is present within the United States plus three corresponding desert populations of a more c ommon variety. To test for clinical variation between mountain and des ert populations, we sampled three elevationally intermediate populatio ns in the San Bernardino Mountains. We recognized a total of 104 band patterns for nine enzymes systems. All nine enzyme systems yielded pol ymorphic zymograms. Although we found substantial intrapopulation vari ability, no significant isozymic differentiation was apparent among an y of the sampled populations. Lack of such differentiation implies tha t the effects of selection or drift have not been felt or detected in these populations. In terms of these enzyme systems Echinocereus engel mannii var. munzii is not distinct from other members of the species. Although there is no evidence of isozymic distinction, morphological e vidence should be included in any decisions to submerge this taxon.