Nomenclatural Novelties in Rosa (Rosaceae) subgenus Rosa Recognized in North America

New taxa and nothotaxa are described within North American Rosa L. subg. Rosa. Rosa setigera Michx., formerly considered of Eurasian origin and placed in Rosa sect. Systylae DC., is segregated into the new Rosa sect. Americanae W. H. Lewis. Its origin is proposed to be in the Ozark Plateau of the south-central United States. One new species, R. memoryae W. H. Lewis, and one new subspecies, R. virginiana Mill. subsp. mini-dentata W. H. Lewis, are described. Twelve new Rosa nothospecies are described: Rosa Xatlantica W. H. Lewis, Rosa Xcanadensis W. H. Lewis, Rosa Xchurchillii W. H. Lewis, Rosa Xfernaldiorum W. H. Lewis, Rosa Xgilmaniana W. H. Lewis, Rosa Xhainesii W. H. Lewis, Rosa Xharmsiana W. H. Lewis, Rosa Xhodgdonii W. H. Lewis, Rosa Xmassiana W. H. Lewis, Rosa Xoldhamii W. H. Lewis, Rosa Xperaxeliana W. H. Lewis, and Rosa Xvictoriana W. H. Lewis. All of these are naturally produced hybrids rather than cultivated plants. The existing nothospecies Rosa Xengelmannii S. Watson, of parentage R. acicularis Lindl. X R. nutkana C. Presl, is divided into three nothosubspecies: nothosubspecies engelmannii, nothosubspecies occidentalis W. H. Lewis, and nothosubspecies britannicae-columbiae W. H. Lewis, distinguished by parentage involving three different subspecies of R. nutkana. New hybrid introgressions identified in Canada and the United States are briefly discussed.