The Inflorescences of the Australian Genera Diplolaena R.Br and Chorilaena Endl (Rutaceae)

Abstract

The inflorescences of five Diplolaena species and of Chorilaena quercifolia were analysed morphologically. Both genera form aggregated, campanulate inflorescences; in Diplolaena they are terminal, standing at the end of leafy shoots, while in Chorilaena they are axillary but with no vegetative 'Unterbau'. As to their position, the inflorescence of Diplolaena is homologous to the whole panicle whereas the inflorescence of Chorilaena is homologous to a branch of it. This study suggests that the basic type of inflorescence in Australian Rutaceae is a determinate panicle which is reduced to few-flowered inflorescences in some species. In both Chorilaena and Diplolaena each flower has a subtending bract and up to two prophylls. In Diplolaena, the showy outer bracts always bear flowers or lateral branches of the inflorescence of first branch order. The inner bracts may be sterile prophylls, indicating a reduction of flowers, or are fertile, subtending flowers of a higher branch order. Thus, the head-like inflorescence of Diplolaena is a reduced panicle. It differs from the inflorescence of Chorileana in the further aggregation of flowers and in the modification of bracts including their enlargement and arrangement into a pseudocorolla; in some taxa (e.g. D. grandiflora) the pseudocorolla is brightly coloured. The two genera have derived inflorescences that have evolved via divergent lines of modification.