Root Parasitism in Castilleja

Plants of eleven Castilleja species have been raised from seed as facultative hemiparasites on all of the several hosts attempted. All were able to complete their life cycle when growing singly without a host. 2. In all species but one, plants growing parasitically showed increased vigor over plants growing without a host. This vigor was expressed by greater height and branching and by earlier flowering. Castilleja plants are able to form haustorial attachments on the roots of other Castilleja plants and apparently derive benefit from this relationship, although to a lesser degree than when a foreign host is parasitized. C. latifolia was the only species in which the plants performed equally well when growing singly or when growing with a host consisting of Chrysanthemum or another Castilleja. 3. A survey of herbarium specimens of Castilleja showed the widespread presence of haustoria. The conclusion was reached that Castilleja, except in rare instances when a host is not available, is a root parasite on hosts from a wide range of angiospermous families.