The biology and systematics of Geranium, sections Anemonifolia Knuth and Ruberta Dum.

Abstract

The external morphology of the six species is considered in detail, special attention being given to the branching System, flower form and the type of seed dispersal, which has often been misunderstood and has parallels among basidiomycete Fungi. In addition petiole anatomy is described, all species being different, and unpublished chromosome counts by other workers are reported (including 2n = 128 for G. canariense, a number erroneously reported earlier for G. palmatum). Crossing experiments (partly carried out by Mr W. Jackson) are described; the only successful new interspecific cross was G. maderense x G. palmatum. It is concluded that the six species, some of which are large pachycaul herbs endemic to Madeira or the Canary Islands, form an advanced group, and their affinities are discussed. A survey of other species with the same seed-discharge mechanism, and of annual or biennial species, suggests that among the latter decrease in chromosome number has taken place along several different lines, and it is suggested that thèse lowered numbers have been combined by amphidiploidy to create new basic numbers in the genus. A formal taxonomic treatment of sections Anemonifolia and Ruberta includes observations on infraspecific variation. An appendix reports the chromosome number of G. cataractarum as 2n = 36.