Dasylirion is a genus of prickly-leaved, dioecious rosette plants found in arid, hilly regions of the desert Southwest and Mexico. Morphological and molecular data clearly indicate that Dasylirion is closely related to Nolina, Beaucarnea, and Calibanus, and these genera are often treated as the family Nolinaceae. Dasylirion was recently monographed and 17 species were recognized. Many of these species fit the model of "semispecies" in which barriers to reproduction are weak and hybrids are common. Species relationships are poorly known, and probably reticulate. Molecular studies using several markers have generally failed to reveal much variation in Dasylirion, a situation common in long-lived, woody taxa. A survey of chloroplast DNA restriction site variation indicated two major groups, one clade of species in southern and central Mexico with brushy leaf tips, and another clade containing the rest of the species. Sequencing ITS rDNA failed to provide much additional information. Recently, a study was made using the technique known as amplified fragment length polymorphism (AFLP) to resolve species relationships in Dasylirion. AFLP is widely used in population level studies, paternity analysis, cultivar identification, and crop breeding, but the limits of using the technique to compare more widely divergent taxa are uncertain. We surveyed 36 samples of Dasylirion using 21 primer pairs, which generated hundreds of variable fragments. In general, the AFLP data supports the clades indicated by the chloroplast DNA restriction site data, however relationships within the major clades is highly dependent on screening the data and methods of analysis. Strengths and weaknesses of using AFLP markers in studies of this nature will be discussed.

Key words: AFLP, Dasylirion, DNA fingerprinting, Nolinaceae, phylogeny