Comparative morphology and phylogeny of Nicotiana section Suaveolentes (Solanaceae) in Australia and the South Pacific

Abstract

Abstract. Molecular phylogenies alone have failed to resolve evolutionary relationships of Nicotiana L. section Suaveolentes Goodsp. (Solanaceae), a section largely comprising Australian endemics. Comparative morphology of Suaveolentes is illustrated and characters, together with the chromosome number, coded for phylogenetic analysis. Morphological characters included discrete characters of seeds and trichomes studied by scanning electron and light microscopy, and gap-coded quantitative measurements of flowers and vegetative organs. These data were analysed using both maximum parsimony and splits network, and compared to and combined with molecular analyses based on published nuclear and chloroplast-DNA sequences. Among morphological characters, there was a high level of homoplasy, possibly attributable to convergent evolution, hybridisation and introgression, and the underlying polyploid origin of the group. There was some conflict between the morphological and molecular datasets; however, overall there was a level of concordance that identified a phylogenetic sequence of taxa that reflected a reduction in the chromosome number.

Karyotypic variation in Nicotiana section Suaveolentes

“…'Corunna' had 32 chromosomes or n = 16 (Fig. 1c), which is consistent with the suggested close association between it and N. goodspeedii (Marks et al 2011), which also has n = 16.…”

“…Seed sources for each taxon used in this study are given in Marks et al (2011) and voucher specimens (lodged at the University of Melbourne herbarium) are listed in Table 1. Seeds were germinated on seedling mix under glasshouse conditions and transferred to 20 L hydroponics tanks when seedlings had three or more non-cotyledon leaves.…”

“…Species for which the chromosome number is unknown include the suggested N. sp. 'Corunna' (Marks et al 2011) and N. fatuhivensis, a former subspecies of N. fragrans which is n = 24. Nicotiana megalosiphon ssp.…”

Time-calibrated phylogenetic trees establish a lag between polyploidisation and diversification in Nicotiana (Solanaceae)

“…The most likely interpretation of the data suggests that the maternal progenitor was a hybrid species formed from the ancestral species of the extant sections Noctiflorae and Petunioides (Kelly et al 2013), although this does not fully account for the variation in all gene trees. It has been suggested that introgression between Suaveolentes species may be widespread (Marks et al 2011b), making species delimitation and phylogeny reconstruction complex because these allopolyploids are hybridising at the polyploid level. However, in four years of fieldwork in Australia (South Australia, Western Australia and the Northern Territory), MWC and SD have yet to observe a specimen that would qualify as a hybrid.…”

Selection of Character Coding Method Is Not Phylogenetically Neutral: A Test Case Using Hominoids

“…In 2001 a new software tool, Tree analysis using New Technology (TNT), was released that provided functionality to analyze continuously scaled characters directly using maximum parsimony [Goloboff et al, 2003]. While the advent of TNT has obviated the need for character coding, many morphological systematists continue to discretize continuously scaled characters prior to analysis [e.g., Welsh et al, 2010;Marks et al, 2011;Soldan et al, 2011;Chartier et al, 2013;Gilbert, 2013;Cichocka and Bielecki, 2015;Devreese and Gilbert, 2015].…”