A literature review of root-parasitism in Scrophulariaceae, Orobanchaceae, and Santalaceae, with some preliminary in vitro studies in Scrophulariaceae

A literature review is presented on five main headings concerning root-parasitic plants in the Scrophulariaceae, Orobanchaceae and Santalaceae. The areas reviewed are in vitro experimentation on root parasites, seed germination, parasite roots and root systems, interaction with hosts, and initiation, development and attachment of the haustorium (the parasitic organ). The concept of advanced versus primitive species is developed. Santalaceae and most Scropulariaceae appear to be unspecialized while Orobanchaceae and the genera Alectra and Striga of Scrophulariaceae seem to show varying degrees of specialization. Trends in specialization appear to be development of and increasing reliance on a primary haustorium, necessity of a host root exudate for seed germination, reduction in root systems and root anatomy and reduction in host range. The genus Lathraea of Scrophulariaceae may present different considerations in specialization. Early results of preliminary in vitro research on several species of parasitic Scrophulariaceae are also presented. Areas touched on are germination, growth in vitro and initiation and self-initiation of haustoria. Finally, an appendix listing known host ranges for many root parasites is included.