The biogeography and systematics of Coriaria (Coriariaceae).

The family Coriariaceae contains the single genus Coriaria. Seemingly isolated from all other families and genera the genus has a unique disjunct distribution covering five separate areas in the northern and southern hemispheres. Possible explanations for this distribution have been explored by studying evolutionary relationships, using cladistic analysis, breeding systems, taxonomy and the fossil record. Characters used in the cladistic analysis have been both phenotypic (morphological, anatomical, phytochemical and cytological) and molecular (sequences of the tRNALeu1 intron of the chloroplast genome). The genus is seen to be probably monophyletic and composed of two monophyletic groups, one in the northern hemisphere and one in the southern. The ancestral taxon was most likely the immediate ancestor of C. terminalis which, while occurring in the Himalayas, is closely related to the southern hemisphere group. From this evidence it is inferred that the genus is ancient with its origin on the Indian plate in the early Cretaceous with the ancestor being rafted to its present position during the break-up of Gondwanaland. The S. and C. American species, C. microphylla, appears to be ancestral to the southern hemisphere group from the molecular evidence, although it is embedded within the southern clade on the basis of phenotypic characters. It is inferred that it arrived in its present position through spread around the Australasian - Antarctic - S. American block of Gondwanaland. The species, C. ruscifolia, is shown to be identical in New Zealand and Chile with identical tRNALeu1 intron sequences. A recent separation into these two areas by dispersal mechanisms would account for this trans-Pacific distribution. New Zealand itself is seen to be a secondary centre of diversity. A formal taxonomic revision has been made in which the original 16 species have been reduced to 13.