Contributions to a chromosome atlas of the New Zealand flora—39. Orchidaceae

Abstract

Somatic chromosome numbers are documented for the majority of the New Zealand indigenous Orchidaceae, with counts for 80 species, 23 taxonomically indeterminate taxa, and 3 hybrids in 34 genera. Related chromosome counts are provided from elsewhere for comparison: 43 species, 12 taxonomically indeterminate taxa, and 4 hybrids in 17 genera from Australia; 1 species from Lord Howe Island; and 4 species in 3 genera from New Caledonia. A wide diversity of chromosome morphology and primary and secondary basic numbers among genera is reported (e.g., x/x2= 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 25, 26, 27). Relatively limited polyploidy was uncovered, confirmed for New Zealand representatives to the tetraploid level (e.g., for the Nematoceras trilobum agg., 2n = 2x2 = 36 → 2n = 4x2 = 72; Drymoanthus, 2n = 2x = 38 → 2n = 4x = 76; and Microtis, 2n = 2x/2x2 = 44 → 2n = 4x/4x 2= 88; in these examples diploid taxa also occur). Amphidiploidy (allopolyploidy) is reported within one genus only, Thelymitra, where it is extensive. Reticulate cytoevolution in Thelymitra is discussed, and the highest chromosome number obtained in this study is 2n = 93 for T. luteocilium from Australia. Extensive aneuploidy appears to be a feature of the Australasian Orchidaceae. Aneuploidy occurs at several levels: within a species (Stegostyla lyallii, 2n = 47, 48; Pterostylis aff. montana agg., 2n = 43, 44; Earina mucronata, 2n = 40, 41, 42; Petalochilus chlorostylus, 2n = 39, 40, 41); between species in the same genus (Hymenochilus, x/x2 of 27→26(→24?); Prasophyllum, x/x2 of 22→21; Adelopetalum, x/x2 of 19→18; Thelymitra, x/x2 of 14→13; Calochilus, x/ x2 of 12→11); between subgenera (Pterostylis subg. Pterostylis, x2 = 2n, derived from x/x2 = 22 found in the other two subgenera); and between related genera (e.g., Molloybas and Singularybas, x2 = 17, from x = 18 elsewhere in the Corybas alliance; Calochilus, x2 = 12, derived from x2 = 13 as found in Thelymitra). The diversity of chromosome morphology and numbers documented here provide independent and informative characters to test the integrity of the recent and extensive generic recircumscriptions of the Australasian Orchidaceae, based on plant macro‐morphology and molecular sequence data. In many cases, the chromosome evidence strongly supports recognition of segregate genera (e.g., for some of the segregate genera of Caladenia, Corybas, Prasophyllum, and Pterostylis) and their subtribal and phylogenetic placements. In other circumstances, the chromosome evidence is uninformative (e.g., for the segregate genera Adelopetalum,Ichthyostomum, and Winika), or else there are indications that certain genera and subtribes remain cytologically heterogeneous and may not be monophyletic (e.g., within Prasophyllum as currently circumscribed).