WOOD ANATOMY OF 4 CALIFORNIAN MISTLETOE SPECIES (PHORADENDRON, VISCACEAE)

Secondary xylem characteristics were compared in four species of Phora dendron Nutt. (Viscaceae) native to California. All have extremely sho rt, thick-walled vessel elements with simple perforation plates. They also share high vessel density, radial vessel arrangement, thick-walle d fibres, and multiseriate, heterocellular rays. The fibres show consi derable intrusive growth. Features of the vessel elements (i.e. vessel dimensions, arrangement, type of wall sculpturing) and calcium oxalat e crystals in the ray parenchyma cells are useful diagnostic traits to separate species. Grooved vessel walls are shared by the morphologica lly similar P. villosum and P. macrophyllum. Differences between these two species may reflect contrasting drought response strategies pursu ed by respective hosts. Vulnerability and mesomorphy ratios of the woo d of FI californicum are higher than those of P. pauciflorum and P. ma crophyllum. Phoradendron pauciflorum has the most xeromorphic wood of the four species studied.