A systematic study of indehiscent-fruited yuccas in the Chihuahuan Desert

Plants of the genus Yucca (Family Agavaceae) are strictly of New World distribution, occurring in the U.S., Mexico, and Central America. Because of the great size of many members of the genus, and because of previous inaccessibility of much of their ranges until fairly recently, little has been done to evaluate the variability within the group. With the exception of Trelease's (1902) work on the genus, other studies have been done strictly within the confines of political boundaries. This is the first to deal with the group within an ecological unit, namely, the Chihuahuan Desert.

Eight taxa of indehiscent-fruited yuccas occur wholly or in part in this area. Of these, six appear as "pairs" that closely resemble each other and possess complimentary ranges (either northsouth or east-west). Data and voucher material consisting of gross plant morphology (measurements), flower, fruit, and leaf measurements, and flavonoid patterns from greenhouse-grown seedlings were taken.

Analyses of these data provided the basis for evaluating not only the amount of variability present in each of the taxa, but to reevaluate the taxonomic alignment of the taxa, as well. It was found that gross plant morphology and fruit morphology provide the most important characters for separating the taxa. Flowers are extremely conservative within the entire genus, but leaves are highly variable, even within a single taxon. The available data has lead to a realignment of the Y_. carnerosana-Y. faxoniana complex to more accurately reflect the probable species alignment, and a combination of two previously recognized species (Y_. torreyi and Y_. treculeana) into a single species (Y. treculeana),