XVI International Botanical Congess

Nucleotide sequences from the internal transcribed spacer (ITS) region of nuclear ribosomal DNA resolve Isoëtes species relationships worldwide. ITS sequences of basic diploids reveal a close and well-supported relationship for several Australasian species. Sequences also show that North American species are not monophyletic. Isoëtes nuttallii and I. orcuttii from western North America form a well-supported clade with European and African species. All other North American basic diploid species form a second clade with relatively little ITS variation. Sequences of a variable intron within the LEAFY gene show promise of resolving relationships within this second clade. ITS and LEAFY sequences are useful in determining parentage of allotetraploids.