SANTALALES

the sandalwood order of flowering plants. It is a miscellaneous collection of plants that has been variously classified to include as few as 5 or as many as 21 families. About 10 families are generally considered to be members of the order, of which 7 form a natural alliance and are in varying degree adapted to parasitic habit, attaching either to the roots or branches of their hosts. Most are tropical or subtropical in distribution, and almost all are evergreen. The perennials, shrubs, and trees that constitute the order range in size from 18 m (60 feet) to the dwarf mistletoe (Arceuthobium minutissimum), one of the smallest of the vascular plants, whose flowering stems extend no more than about 3 mm (0.1 inch) from the host plant. Many members of Santalales have long been important for their use in religious rituals and folk customs. The Christmas mistletoe (Viscum album), known for centuries before the birth of Christ, is used by Christians throughout Europe and North America during the Christmas season. Sandalwood was used in religious ritual in Egypt as early as 1700 BC and probably earlier in Asia, where it is prized today by Hindus, Buddhists, Parsis, and the Muslims of Southeast Asia. It is also used for wood carving and as a source of oil. The mistletoessuch as the genera Dendropthoe of India and Struthanthus of tropical Americaare significant also because they cause serious damage to such economically important plants as cacao, rubber, and citrus and other fruit trees. Members of Arceuthobium attack the conifers of western North America, while members of Phoradendron attack walnuts, oaks, and some conifers of the United States. All known members of seven of the families of Santalales are parasites. The most obvious evidence of parasitism in these plants is the occurrence of the haustorium, a specialized organ that penetrates the living tissue of its host and absorbs water and nutrients, transferring them to the parasite through partial fusion of the xylems (water-conducting tissues) of the host and parasite. In most members of the Viscaceae, the haustorium fragments and branches out through the host's softer tissues. In some species of Arceuthobium, a threadlike system develops that may reach into the growing point of the host. Nearly all members of the Santalales have simple leaves that lack stipules. A few species have surface hairs on their leaves or stems. In the Balanophoraceae and some other parasites, leaves are reduced to scalelike organs. Flowers of many members of the order have either petals or sepals or neither, although some have both. The stamens (male) usually equal the number of petals and occur opposite the lobes of the petals. In most members of the order, the ovary (female) is inferior in position. Ovules (developing seeds) are few. Members of the Olacaceae produce rather large nuts, while the Balanophoraceae have minute fruits. The solitary seeds, containing endosperm (special nutrient tissue), are usually dependent upon birds for their dispersal.