Description and Phylogenetic Position of a New Angiosperm Family, Guamatelaceae, Inferred from Chloroplast rbcL, atpB, and matK Sequences

The monotypic genus Guamatela was originally described from Guatemala and has also been collected in Honduras and Mexico. This taxon has been placed in tribe Neillieae of Rosaceae based on its follicular fruits and persistent stipules, but it is anomalous in the tribe due to lack of endosperm, while some of its other characters, such as opposite leaves, lack of a well developed hypanthium, and fused styles, are unusual for the entire family. No other taxonomic placement has ever been proposed for Guamatela, however, and morphological characters alone do not suggest any likely alternative. DNA was extracted from two herbarium specimens of G. tuerckheimii, one collected in the state of Oaxaca, Mexico in 1969 and the other in the department of El Progreso, Guatemala in 2000. Phylogenetic analyses of the chloroplast rbcL, atpB, and matK genes amplified from the materials, along with sequences from representatives of most major eudicot groups, strongly support Guamatela as a member of the rosid order Crossosomatales, as circumscribed in APG II. None of the molecular data supports the inclusion of Guamatela in any described family in the order, and the unique combination of morphological characters does not fit the description of any of those families. Based on these results, we here propose the new family Guamatelaceae to accommodate this genus.