The Genetic Identity and Range of Rumex orthoneurus (Polygonaceae)

Rumex orthoneurus Rech.f. (Polygonaceae) is a rhizomatous, herbaceous perennial that grows in riparian and wetland habitats in the mountains of central and southern Arizona, southwest New Mexico, and northern Sonora, Mexico. Because of declining populations in National Forest lands, it is listed as a “sensitive species'' by the U.S. Forest Service and it is also listed as a rare plant in Arizona. Recent taxonomic treatments are conflicted in how they treat R. orthoneurus- either as a distinct species or as a synonym of Rumex densiflorus Osterh., which is more widespread and not considered rare or threatened. Therefore, a better understanding of the taxonomic status of R. orthoneurus will inform land managers and scientists if it warrants conservation concern. The main purpose of this study was to use nuclear ribosomal ITS1-5.8S-ITS2 sequence data from both herbarium specimens and GenBank to generate a phylogeny of Rumex to test the status of R. orthoneurus as a distinct taxon. Additionally, the 2C DNA content (genome size) for four species of Rumex was measured with flow cytometry to determine if the 2C DNAs content can potentially be used to differentiate R. orthoneurus from other species in the genus. In total, 133 sequences from 87 herbarium specimens and 46 Genbank sequences were included in phylogenetic trees. The phylogenetic data suggests that R. orthoneurus, is nested in a well-supported but unresolved clade with Rumex pycnanthus, and R. densiflorus, and supports treating R. orthoneurus and R. pycnanthus as synonyms of R. densiflorus. Therefore, the distribution of the species within the “Rumex densiflorus” group is likely more widespread than originally thought, which may affect management decisions for R. orthoneurus. Flow cytometry and morphological data suggests that mixed Rumex accessions can be identified, and the seed germination test indicates the long-term viability of “R. densiflorus” clade seeds.