The genus Melampodium consists of 40 species distributed throughout Mexico and Central America with extensions into the southwestern United States and Colombia and Brasil of South America. The genus reflects broad chromosomal evolu - tion involving dysploidy and polyploidy withn = 9, 10, 11, 12, 14, 18, 20, 23, 24, 27, 28, 30, and 33 having been documented (x = 9, 10, 11, 12, and 14). The most recent classification of the genus, based primarily on morphology and chromosome num bers, recognized six taxonomic sections: Alcina, Bibractiaria, Melampodium, Rhizomaria, Serratura, and Zarabellia. Section Melampodium, which contains 22 species, was divided into five series: Cupulata, Leucantha, Longipila , Melampodium, and Sericea. This hypothesis had been tested by previous morphological phenetic and cladistic analyses, and several problem areas had been highlighted, especially involving section Alcina, but no modifications to the classification have been made. Recent molecular studies utilizing nrITS, 5S rDNA spacer and low-copy nuclear PgiC gene, plus plastid matK and psbA-trnH regions allow the classificatory hypothesis to be tested more precisely. Congruence between ITS and matK phylogenies for all species reveals sections Bibractiaria, Rhizomaria, and Serratura to be holophyletic. The largest section Melampodium is holophyletic with both plastid markers, but M. longipilum is shown as an outlier (tying to sect. Rhizomaria) in all nuclear marker phylogenies (ITS,PgiC and 5S rDNA spacer). SectionZarabellia appears holophyletic inmatK but biphyletic with ITS, suggesting recogni tion of two distinct series. Section Alcina is the most problematic, being triphyletic in ITS and matK, and with the species not connecting to the same relatives. These insights recommend recognition of three sections from within section Alcina, one hous ing M. nutans (Nutantia Stuessy, sect. nov.) another M. glabrum (Glabrata Stuessy, sect. nov.) and a third M. perfoliatum (sect. Alcina (Cav.) DC.). These may represent ancient independent lines that have diverged from original x = 11 ancestors. Within section Melampodium, 5S rDNA NTS, PgiC and psbA-trnH, in addition to ITS and matK, provide insights on relationships among taxonomic series. Series Leucantha and Longipila are holophyletic, and series Cupulata nearly so, with M. glabribracteatumdeserving treatment in a series of its own. The most complex relationships are between series Melampodium, Cupulata, and Sericea, the latter comprising five exclusively polyploid taxa (4 x and 6 x). Molecular and cytogenetic data reveal allopolyploid origins for all of these polyploids, in some cases involving hybridization between the two series Cupulata and Melampodium / Sericea, such as with M. mayfieldiiand M. longicorne, which exacerbates taxonomic circumscription.
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