Authors have debated the taxonomic rank of Juncus longii almost since its description in 1937. Some authors treat the J. marginatus complex, to which J. longii belongs, as comprised of three species (J. biflorus, J. longii, and J. marginatus), whereas other authors recognize only one species (J. marginatus). Univariate and multivariate statistical analyses of measurements of twelve morphological characters suggest that Juncus longii is a species distinct from J. margintatus and J. biflorus. Ecological differences are also apparent. Juncus longii is restricted to early successional seepages with exposed soils. Juncus marginatus and J. biflorus, however, are found in less specialized habitats. Syntopic occurrences of J. longii with J. marginatus and J. longii with J. biflorus suggest the morphological differences used to identify these species are not a reflection of environmental conditions. Juncus longii is endemic to the southeastern United States, whereas J. biflorus and J. margintatus are more broadly distributed across eastern North Americia, Central America, and central South America.
Knapp, W.M. & R.F.C. Naczi. 2008. Taxonomy, Morphology, and Geographic Distribution of Juncus longii (Juncaceae). Systematic Botany 33(4): 685–694. https://doi.org/10.1600/036364408786500145
Wesley Knapp 
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