Morphology, geographic distribution, and host preferences are poor predictors of phylogenetic relatedness in the mistletoe genus Viscum L.

Besides their alleged therapeutic effects, mistletoes of the genus Viscum L. (Viscaceae) are keystone species in many ecosystems across Europe, Africa, Asia and Australia because of their complex faunal interactions. We here reconstructed the evolutionary history of Viscum based on plastid and nuclear DNA sequence data. We obtained a highly resolved phylogenetic tree with ten well-supported clades, which we used to understand the spatio-temporal evolution of these aerial parasites and evaluate the contribution of reproductive switches and shifts in host ranges to their distribution and diversification. The genus Viscum originated in the early Eocene in Africa and appeared to have diversified mainly through geographic isolation, in several cases apparently coinciding with shifts in host preferences. During its evolution, switches in the reproductive mode from ancestral dioecy to monoecy imply an important role in the long-distance dispersal of the parasites from Africa to continental Asia and Australia. We also observed multiple cases of photosynthetic surface reduction (evolution of scale leaves) within the genus, probably indicative of increasing specialization associated with the parasitic lifestyle. Even compared with other parasitic angiosperms, where more host generalists than specialists exist, Viscum species are characterized by extraordinarily broad host ranges. Specialization on only a few hosts from a single family or order occurs rarely and is restricted mostly to very recently evolved lineages. The latter mostly derive from or are closely related to generalist parasites, implying that niche shifting to a new host represents an at least temporary evolutionary advantage in Viscum.

[Morphological, microscopical and UV spectral identification of herba visci ovalifolii].

OBJECTIVE: To identify herba Visci ovalifolii, Chinese medicinal materials used in Li and Miao nationalities. METHODS: Morphological, microscopical and UV spectral methods. RESULT: Dichotomous branch with a yellow surface, with leaf of 3-5 acrodromous veins originating at the base of the leaf. In transverse section, the thick outer wall of the epidermis of stem projecting like nipple; stone cells contain frequently a prismatic crystal of calcium oxalate, often occur in the cortex and phloem of the stem. Pericycle fibres and xylem fibres all with a well-developed thick wall; vessels with a bordered pits somtimes have a spiral thickened interwall; mesophyll homogeneous contain cluster crystals (not calcium oxalate); stomata present on both surfaces, mostly paracrytic, with small and narrow subsidiary cells. Hairs absent at the surface. CONCLUSION: Above morphological and microscopical characters may be used for the identification of herba Visci ovalifolii. UV spectral method is a simple identificating method for herba Visci ovalifolii.