Instability and Incongruence in the Brooms and Gorses (Leguminosae Subtribe Genistinae)

Abstract

The Genistinae is a subtribe of the Leguminosae and contains 196 species, of which most are yellow-flowered shrubs (‘gorses’ and ‘brooms’) confined to Europe (Bisby, 1981). The subtribe is of interest for taxonomic theory because of persistent difficulties in grouping the species into genera. Even before the advent of chemical systematics and numerical taxonomy, taxonomists concerned with the Genistinae were familiar with the problems caused by species resembling one group in some characters and another in other characters — the phenomenon we now call incongruence. They reported ‘reticulation’, meaning in this case a network of resemblances between small groups of species. For example, a group of 10 species found in S. Europe and the Canary Islands was classified as a distinct genus, Teline, by Gibbs and Dingwall (1971) on the basis of distinctive leaf traces; as part of the large genus Cytisus by Hutchinson (1964) on account of the seed aril and leaf morphology; and as part of the large genus Genista by Polhill (1976) on account of many floral characters including wing petal shape and calyx lobing. Polhill (1976) lists 20 different classifications published between 1825 and 1968 and confusingly four of these, by Hutchinson, Rothmaler, Polhill, and Gibbs & Dingwall, are still in use.