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The relationships of Rosa gymnocarpa Nutt. in connection with historical sect. Gymnocarpae Crép. and recent publications on Rosa phylogeny are discussed, noting the relative isolation of the species within the genus. All synonyms and segregate taxa are addressed; a lectotype is designated for the species and other names as needed. Two subspecies are recognized: subsp. gymnocarpa, primarily west of the Cascade-Sierra axis, and subsp. helleri (Greene) Ertter & W. H. Lewis, occurring from southeastern British Columbia and northwestern Montana to the northern Sierra Nevada in California. Subspecies gymnocarpa is further divided into var. gymnocarpa and var. serpentina Ertter & W. H. Lewis. A key, range descriptions, and representative specimens are provided for infraspecific taxa. Extensive zones of intergradation occur where the ranges intersect, especially in the Klamath and Siskiyou ranges of northeastern California and adjacent Oregon; intermediates are also common in northern Idaho and adjacent states and provinces. Presumed hybrids with sympatric species are discussed, including some across ploidy levels. Nothospecies R. ×henryana W. H. Lewis is described for the hybrid of R. gymnocarpa and R. nutkana C. Presl; R. ×collaris Rydb. (pro sp.) is transferred to nothospecies status as the hybrid of R. gymnocarpa and R. woodsii Lindl.
Published in Madroño 2016 v.63 no.3, pp. 268-280
