Arceuthobium Gillii and A. Nigrum (viscaceae) revisited: Distribution, morphology, and RDNA-its analysis

Additional morphological, phenological, and molecular data were obtained for Arceulhobium gillii and A. nigrum from throughout their geographic distributions in northern Mexico and southern Arizona. Multivariate analysis of variance (MANOVA) and discriminant function analysis demonstrated that A. gillii and A. nigrum are distinguishable morphologically. Discriminant function analysis also indicated that the dimensions of the third internode (length and width) and basal diameter of female and male plants contributed most to the classification and predication of species. Significant differences in plant height (female and male) as well as flower and fruit dimensions were also evident between these dwarf mistletoes, A. nigrum having larger dimensions for each of these characters. Although A. nigrum purportedly flowers twice annually (spring and fall), our observations indicated that the period of anthesis for this mistletoe occurs only once annually-fall to early winter. In contrast, A. gillii flowers in the spring; thereby, suggesting that these taxa likely are reproductively isolated. Phydogenetic analyses of nucleotide sequences of the rDN A internal transcribed spacer (ITS) region delineated both taxa, resolving A. gillii to a monophy-letic clade strongly supported by bootstrap and Bayesian credibility values. Collectively, A. gillii and A. nigrum are well-defined morphologically and distinguishable molecularly, supporting the classification of these taxa at the specific rank.