A Monograph of the Genus Rosa in North America. I. R. Acicularis

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Abstract
Rosa acicularis Lindl., the only species ofRosa indigenous to both North America and Eurasia, has the most extended distribution of any species in the genus. The populations ofR. acicularis Lindl. in North America and Eurasia differ by nine morphological characters: pedicel glandulation, auricle width, number of serrations per half leaflet, kind of leaflet serration, serration glandulation, leaflet glandulation, petiole bristles, number of leaflets per leaf, and width of the sepal. Morphologically intermediate as well as typical North American and Eurasian individuals occur in Alaska and eastern Siberia. Approximately 1000 pollen grains measured for representatives of this species in both continents (North America, x = 38.5 μ.; Eurasia, x = 40.4 μ) illustrate a significant difference in size between the North American diploid (x = 27.9 μ) and tetraploid (x = 33.4 μ) species. The percentage of abortive pollen for 24 individuals selected at random throughout the range of the species is low. Only one plant from Alaska, found to be morphologically intermediate between the two populations, had highly abortive pollen (65%). Rosa acicularis Lindl. is hexaploid (2n = 42) in chromosome number in North America and octoploid (2n = 56) in Eurasia. From gross morphological, phytogeographical, and cytological evidences,R. acicularis Lindl. has been separated into two subspecies,R. acicularis Lindl. subsp.acicularis in Eurasia andR. acicularis Lindl. subsp.sayi (Schw.) Lewis in North America. The first heptaploid (2n = 49) chromosome number inRosa is recorded for an artificial hybrid from these subspecies. About fifty binomials, trinomials, pre-Linnaean phrases, and misapplied species names are listed under the subspecies.

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