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Molecular and cytological examination of Calopogon (Orchidaceae, Epidendroideae): circumscription, phylogeny, polyploidy, and possible hybrid speciation¹

²Section of Integrative Biology and Plant Resources Center, University of Texas, Austin, Texas 78712 USA; ³Deptartamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, BR116, Km3, Campus Universitário, 44031-460, Feira de Santana, Bahia, Brazil; ⁴Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3DS UK

ABSTRACT

The orchid genus Calopogon R.Br. (Orchidaceae), native to eastern North America and the northern Caribbean, currently contains five species and up to three varieties. Using nuclear internal transcribed spacer (ITS) ribosomal DNA sequences, amplified fragment length polymorphisms (AFLPs), chloroplast DNA restriction fragments, and chromosome counts, we present a phylogenetic and taxonomic study of the genus. Calopogon multiflorus and C. pallidus are consistently sister species, but the relationships of C. barbatus, C. oklahomensis, and C. tuberosus are not as clear. In the ITS analysis C. oklahomensis is sister to C. barbatus, whereas it is sister to C. tuberosus in the plastid restriction fragment analysis. Furthermore, all species were found to have chromosome numbers of 2n = 38 and 40, with the exception of the putatively hybrid-derived C. oklahomensis with 2n = 114 and 120. The hexaploidy of the latter, plus the discrepancy in its position between the ITS and plastid restriction fragment trees, could suggest that it is of hybrid origin. However, the presence of unique morphological and molecular characters might indicate that it is either an ancient hybrid or not of hybrid derivation at all. Finally, using these molecular methods all taxa appear to generally be discrete groups, with the exception of C. tuberosus vars. latifolius and tuberosus, the former of which is best combined with the latter.

Key Words: AFLP • Calopogon • circumscription • Orchidaceae • phylogeny • polyploidy • plastid DNA • ribosomal DNA

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