Chromosome number variation in two antipodean floras.

Area of Science:

• Plant biology
• Evolutionary biology
• Cytogenetics

Background:

• Chromosome number (CN) variation is a key evolutionary driver.
• Comparing antipodean floras (Italy vs. New Zealand) offers insights into biogeographic and taxonomic influences on CN.
• B-chromosomes represent a distinct layer of genomic variation.

Purpose of the Study:

• To compare chromosome number (CN) variation between Italian and New Zealand floras.
• To determine if CN patterns reflect latitudinal range or biogeographic/taxonomic context.
• To investigate differences in B-chromosome frequency, number, and distribution.

Main Methods:

• Comparative analysis of two large cytotype datasets (Italy: 3426, New Zealand: 2525).
• Taxonomic order and vascular plant phylogeny comparisons.
• Statistical analyses including ANOVA and Kruskal-Wallis tests.

Main Results:

• New Zealand's vascular flora has approximately double the mean CN compared to Italy's.
• Higher mean CN values in New Zealand are statistically significant across most orders.
• CN variation differences exist among orders and clades, independent of geography; no CN-B-chromosome correlation found.

Conclusions:

• Extensive polyploidization is a major factor in New Zealand vascular flora evolution, linked to high endemism.
• Latitudinal gradient hypothesis for polyploidy increase is challenged; bioclimatic gradients may be more influential.
• Geographic adaptive roles of B-chromosomes might relate to frequency rather than number.