Morphological and genetic variation in the Senecio pinnatifolius complex: are variants worthy of taxonomic recognition?

Abstract

The current taxonomy of the Senecio pinnatifolius complex (formerly Australian S. lautus) is inadequate in describing intra-specific variation. We present several putative taxa as alternatives to current subspecies, based on variants observed during both herbarium surveys and field studies. We sought to establish whether these taxa were objectively justified in terms of morphology and genetic relationships. This was done in three ways. First, a morphometric study of plants grown under standard conditions was undertaken. Second, isozymes were analysed to establish genetic relationships within the complex. Third, achene morphology was examined by scanning electron microscopy. Variants from central Queensland (BRIGALOW V.) and the deserts of central and Western Australia (DESERT V.) were clearly separated from all other variants based on the number of involucral bracts. This differentiation into two major groups may warrant subspecific recognition. Although variation within each of the proposed subspecies was continuous, separation of variants was possible based on statistical survey. This is consistent with their formal recognition as varieties. Further work is required to determine correct nomenclature of proposed subspecies and varieties, and to fully elucidate variation and provenance in inland forms.