Modes of union and interaction between parasite and host in the Loranthaceae - V. Some South African Loranthoideae

Abstract

Haustorial structure and behaviour are described for three South African species: Loranthus elegans ( Moquinia rubra ), L .( Tapinanthus ) prunifolius and L . ( Taxillus ) glaucus . Fundamental differences are revealed between them, although they are nearly related. In Moquinia rubra the haustorium extends against the wood and maintains contact by a meristematic surface layer with large parts of the host cambium, which continues to function, but forms only phloem where in contact with the haustorial meristem. In Tapinanthus prunifolius the haustorium spreads against the wrood, but interrupts the cambium and links up with the phloem ; numerous xylem connexions are established between radial surfaces of host wood and parasite. In both these species variations are described, attributable to relative age and vigour of host and parasite, or, in Moquinia rubra , to a different host. In Taxillus glaucus the haustorium does not penetrate to the cambium but spreads and branches in the outer tissues below the periderm, and then sends m any fine sinkers radially to the wood, where they become embedded like coarse medullary rays, including xylem elements. This aberrant form is closely matched by an unrelated American species, Psittacanthus sternbergianus , described by Solms-Laubach. Reference is made to still another type of attachment, the ‘wood-rose’ type, already described for a South African species, L . ( Erianthemum ) dregei , and a similar specimen is illustrated.