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.
An isozyme and morphological study of
Senecio madagascariensis Poir. and closely related
species in Australia, South Africa and Madagascar was used to investigate the
most likely region of origin for Australian plants known as fireweed.
Collections of seed and voucher specimens were made in New South Wales,
KwaZulu-Natal, East and West Cape Provinces and southern Madagascar and
specimens classified according to recognised taxa or descriptive variants.
Plants were characterised by using isozyme analyses and morphological
observations of both voucher specimens and achenes. Australian fireweed
populations were found to be most closely related to populations of
S. madagascariensis from KwaZulu-Natal in South Africa,
and to be more distantly related to populations from East and West Cape
Provinces in South Africa and from Madagascar. The implications of these
findings are discussed in relation to efforts to locate host-specific
biological control agents for fireweed.
Chromosome counts of 2n = 20 for specimens of Senecio madagascariensis from Australia and from Madagascar are reported. By contrast, counts of 2n = 40 for a diversity of specimens of the S. lautus sensu lato complex are reported. These results support previous separation of these taxa on morphological grounds.
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