Population Biology and Habitat Relations of Some Hemiparasitic Scrophulariaceae

Abstract

Heute falsche Familienzuordnung!! Recent information is reviewed on the population biology and habitat relations of some hemiparasitic Scrophulariaceae (Pedicularis, Rhinanthus, Melampyrum, Odontites, Euphrasia and Parentucellia species). The species occur in a wide range of habitats; they are not host specific, except perhaps for Melampyrum sylvaticum in field conditions. A wide range of hosts may be parasitized, but a high inter- and intra-specific variation of ‘host quality’ was observed. There is also intra-specific variation of the parasitic ability of the parasites. These may reduce the development of their hosts, and so may affect the composition of a vegetation. The demographic processes vary with field conditions — both in space (soil conditions, height above the water table) and time (position in a succession sequence) — and between ecotypes. The wide morphological variation of the annuals with respect to node number and flowering time can be related to the length of the growing season; the variation with respect to growth habit and leaf morphology is related to vegetation structure. Such relations may exist because of high light requirements, or because microclimate affects the balance between the hydrostatic pressures of host and hemiparasite, the driving force behind the transport system between the two.