A Contribution to the Cytology of the Australian-South Pacific Species of Nicotiana

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Abstract
The 15 Australian-South Pacific spp. of Nicotiana, or the Suaveolentes section of the subgenus Petunioides, are a geographically isolated group of complexly interrelated herbaceous spp., the specific differences of which are generally of small magnitude. 13 have been studied cytologically. 4 16-paired spp., one 18-, two 19-, two 20-, one 21-, one 22- and two 24-paired occur. Usually, as chromosome no. increases the no. of chromosomes with subterminal centromere increases at the expense of those with median or submedian. 26 hybrids involving 12 spp. show considerable to high pairing in the 1st meiotic meta-phase. This indicates a common origin. A phyletic cyto-logical hypothesis involving a base no. of 8 and repeated hybridization, in part accompanied by chromosome doubling, is offered as a possible interpretation of chromosome no., morphology and behavior in the Suaveolentes.

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