Introduction

More has been written about Viscum album L., the common European species, than any other mistletoe. Indeed for many centuries, Viscum album, and to a lesser extent Loranthus europaeus L., the only other European mistletoe, epitomised what was known about this intriguing group of plants. As other parts of the world were explored many more shrubby plants were discovered that grew exclusively on other woody plants and had an intimate connection, the haustorium, that enabled them to extract solutes and water from their hosts. Most of them had fruits similar to the common European mistletoes, with a highly viscous middle layer to the fruit wall that stuck the seed to a branch when deposited there by a bird. Distinctive features were found in some genera. Some species from southern South America and Australia are root parasites, growing into lianes or small trees. The Australian Christmas tree, Nuytsia floribunda R. Br., is notable as being a small tree, but also for having dry, winged fruits. The dwarf mistletoes attributed to the genus Arceuthobium, are serious parasites of conifers in the northern hemisphere. They are dispersed by tiny seeds squirted considerable distances by water pressure built up in the small fruits. Overall, however, the mistletoes were considered to share sufficient features for all to be included in a single family, Loranthaceae, by most botanists until the middle of this century. In the census by Engler & Krause in the second edition of Engler & Prantl's Die natürlichen Pflanzenfamilien in 1935 some 1,000 species were included in the family.

It is now apparent that many of the features shared by mistletoes are also found in other families of the order of sandalwoods, the Santalales. The Loranthaceae and Viscaceae are now considered to be of separate origin within that order. The special adaptations for an aerial existence seem to have arisen separately in the two groups.

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