Native California Roses

prepared by Barbara Ertter, 2001

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The genus Rosa is extremely well-known as one of the most popular of flowers, with a long history of cultivation and an abundance of hybrid forms. An abundance of native species occur throughout the northern hemisphere, from Arctic regions south to Mexico, northwestern and eastern Africa, India, and southeast Asia. Numerous Eurasian species have been used in the development of a spectacular diversity of cultivated roses. Although native Californian species have played little (if any) part in this hybridization process, several are known in cultivation as species roses. Krüssmann (1981), for example, includes R. californica Cham. & Schldl., R. gymnocarpa Nutt., R. minutifolia Engelm., R. nutkana Presl, R. pinetorum A.A. Heller [probably equivalent to R. bridgesii], R. pisocarpa A. Gray, and R. spithamea S. Watson in his list of species known from cultivation, with R. californica furthermore having three named cultivars: 'Ardens,' 'Nana,' and 'Plena.' [Link to more information on R. californica hybrids and cultivars.]

A major difficulty when dealing with native roses is the complex nomenclatural history. At least 4,000 different species have been described at one time or another, and the various names have been applied in a shifting manner. For example, it is unlikely that Krüssman's reference to R. pinetorum, cited above, refers to the same entity that goes by this name in The Jepson Manual (Ertter, 1993). As noted on the taxonomic decision-making page, the reason for the tremendous uncertainty in the number of species of Rosa is largely because the genus refuses to resolve itself into a tidy set of unequivocal species, under any species concept. The relatively few morphological characters that can be used to distinguish species tend to be highly plastic, capable of varying significantly within populations or even within the same individual, depending on growing conditions. To make matters worse, the relative ease with which roses hybridize, the very characteristic that has ensured their popularity with horticulturalists, wreaks havoc on the hard-pressed systematists' efforts to come up with a stable, scientifically based taxonomic treatment of Rosa.

This situation most definitely applies to the genus in California. At one extreme, a grand total of nearly 60 species names have been proposed and applied to the native roses of California at one time or another, with the majority described by Edward Lee Greene and Per Axel Rydberg in the early 1900's (e.g., Greene, 1912; Rydberg, 1917, 1918). Greene defended his new species with the claim that they were all "invested with diagnostic characters more pronounced than most of the published species of Rosa have to show" (Greene, 1912, p. 255). In Rydberg's 1918 treatment of Rosa for North America, the most recent attempt to provide uniform monographic coverage of the continent, nearly 40 different native roses were recognized as occurring in California. This was a radical increase from the three recorded as occurring in California by Sereno Watson (1885), in the previous comprehensive revision of North American roses.

This situation was reversed in the 1930's when Eileen Whitehead Erlanson applied the newly developed principles and methodologies of biosystematics, including cytogenetics and experimental hybridization, to the native roses of North America. She also conducted extensive field observations of natural populations of western roses (Erlanson, 1930) and common garden experiments at the University of Michigan and at the California Institute of Technology in Pasadena, California (Erlanson, 1932; 1934). As a general conclusion, Erlanson noted that "It is not impossible to find on the same bush two of some of the species listed by Rydberg" (Erlanson, 1934, p. 204). As a result, she drastically reduced the number of species recognized by Rydberg, accepting only 21 Linnaean-type species ("linneons," in biosystematic parlance) of native roses in all of North America, including Mexico (Erlanson, 1932 & 1934). Following biosystematic procedures, she also recognized seven "ecotype species" and an additional six F1 hybrid species, but this is still a far cry from the 129 species of North American roses accepted by Rydberg (1918). Only eight of Erlanson's 34 species (linneons + others) were treated as occurring in California; i.e., less than one-fourth of the number recognized by Rydberg. This included six linneons (R. californica, R. gymnocarpa, R. durandii Crépin, R. pisocarpa, R. spithamea, R. woodsii) and two ecotype species (R. calvaria Greene and R. yainacensis Greene, the latter including R. pinetorum).

In spite of the strong scientific underpinning of her studies, Erlanson's specific taxonomic conclusions were not adopted in subsequent floristic treatments addressing the native roses of California (see concordance of treatments), beyond the generalized agreement that Greene and Rydberg had recognized too many unsupportable taxa. Jepson (1936), in his exhaustive Flora of California cited Erlanson's papers in the bibliography for Rosa but apparently relied on his own observations and interpretations as the basis for his classification. Jepson suggested, for example, that the R. californica complex "represents a 'hybrid swarm' and that the occasional outstanding specimens result from chance combination of independently varying characters of an interbreeding population. . . . In the artificial groupings which result from [classification] attempts, there are usually few or no specimens closely approximating the type, and plants representing unnamed associations of characters are as frequent as those which have been designated as species or varieties" (p. 209). His treatment consisted of 7 species, five of which (nutkana, woodsii, spithamea, gymnocarpa, pisocarpa) contained an additional variety. Erlanson's R. yainacensis became a synonym of R. nutkana, R. calvaria was replaced by R. pinetorum, and the fate of R. durandii was not explicitly addressed.

Subsequent treatments provided only the most abbreviated explanations for their taxonomic decisions (e.g., "Some of these variations [in R. gymnocarpa] have been described as distinct species but no constant character has been found to warrant such treatment" [McMinn, 1951]), without reference to either Erlanson or Jepson. Abrams (1944) and McMinn (1951) each independently reduced Greene's and Rydberg's plethora of species to a more manageable handful. Of the 21 native roses given full or tentative acceptance by Abrams (1944) in his Illustrated Flora of the Pacific States, 15 occurred in California, only partially overlapping Erlanson's or Jepson's taxonomy. As key differences, Abrams recognized R. pinetorum, R. aldersonii Greene, R. ultramontana S. Watson, R. gratissima Greene, R. rivalis Eastw., R. mohavensis S.B. Parish, and R. sonomensis Greene, all placed in synonymy by Erlanson, and used R. bridgesii Crépin instead of R. calvaria.

McMinn (1951), in his Illustrated Manual of California Shrubs, took a more conservative stance than Abrams, accepting eight native species and two additional varieties, in the process dropping both R. yainacensis and R. calvaria/bridgesii without comment. McMinn's treatment, as modified by the results of Cole's (1956) analysis of the Rosa californica complex, apparently forms the basis for the treatment of Rosa in Munz's (1959) Flora of California. Munz's Flora gained acceptance as the floristic standard of California botany for over three decades, during which time the contentious and still unresolved nature of Rosa taxonomy became largely forgotten.

My own involvement and expertise with Rosa originates with my agreement to prepare a treatment of the genus for a new edition of The Jepson Manual (Ertter, 1993). It may come as a surprise to rose fanciers that this was done only after no other contributor to the Manual had asked to do Rosa, such that one of the in-house contributors had to bite the bullet and prepare a treatment with the deadline fast approaching. As the contributor who had already prepared treatments of most herbaceous Rosaceae (e.g., Potentilla, Ivesia), I figuratively drew the short straw. This meant I had less than a month to familiarize myself with native and naturalized Rosa in California, critically evaluate previous treatments (e.g., Munz, 1959), draw my own conclusions, and summarize the results in the structured format that had become known as "Jepsonese."

Because this last flurry to finish the Manual happened during the dead of winter, I was also dependent on existing dried specimens in herbaria, supplementing the collections at the University of California at Berkeley (UC and JEPS) and the California Academy of Sciences (CAS and DS) with loans from Rancho Santa Ana Botanic Garden (RSA and POM), Humboldt State University (HSC), and San Diego Museum of Natural History (SD). Being unfamiliar with the complex and unresolved history of Rosa taxonomy in California, I used the treatment in Munz as a starting point. However, I quickly became dissatisfied with existing delimitations and keys, and accordingly experimented instead with alternative circumscriptions, diagnostic characteristics, and dichotomous key couplets. The result was the treatment that appeared in The Jepson Manual (Ertter, 1993) and that forms the basis for this website (see taxonomic decision-making page for philosophical underpinning). The main differences from the treatment in Munz include a radical realignment of the spithamea-pinetorum-bridgesii complex, and a possibly overly conservative lumping of some varieties recognized by Munz (see concordance of treatments by Watson, Rydberg, Erlanson, Jepson, Abrams, Munz, and Ertter).

Because I was very much aware that I was going out on a limb in diverging radically from some aspects of Munz's treatment, I was eager to put my revised taxonomic hypotheses to a variety of tests that could not be pursued until the following field season, well after the cut-off date for the Manual. These tests, which are still on-going, include the following activities, paralleling some of those carried out by Erlanson:

To my vast relief, most of these studies have supported rather than contradicted my conclusions in The Jepson Manual. As is normal, however, not only do many questions still remain unresolved, but new problems have been subsequently brought to light. With luck, an improved understanding of these "thorny" questions will result from a developing collaboration with Walter Lewis, who is preparing the treatment of Rosa for Flora of North America, and with the Anne Bruneau lab, who are undertaking molecular phylogenetic studies of Rosa. Stay tuned!


Abrams, Leroy R. 1944. Illustrated Flora of the Pacific States: Washington, Oregon, and California. Vol II: Polygonaceae to Krameriaceae. Stanford University Press, CA. 635 pages.

Cole, Donald. 1956. A revision of the Rosa californica complex. American Midland Naturalist 55: 211--224.

Erlanson, Eileen W. 1930. Field observations on wild roses of the western United States. Papers of the Michigan Academy of Science, Arts and Letters 11: 117--135.

_______. 1932. American wild roses. The America Rose Annual 1932: 83--90.

_______. 1934. Experimental data for a revision of the North American wild roses. Botanical Gazette 96: 197--259.

Ertter, Barbara. 1993. Rosa. In: Hickman, J.C. (ed.) The Jepson Manual: Higher Plants of California. University of California Press, Berkeley, CA, pp. 972--973.

Greene, Edward L. 1912. Certain western roses. Leaflets of Botanical Observation and Criticism 2: 254--266.

Jepson, Willis Linn. 1936. A Flora of California. Vol. 2: Capparidaceae to Cornaceae. Associated Students Store, University of California, Berkeley.

Krüssmann, Gerd. 1981. The Complete Book of Roses. Timber Press, Portland, OR. 436 pages. [translation by G. Krüssman & N. Raban of Krüssman, G., 1974, Rosen, Rosen, Rosen]

Munz, Philip A. 1959. A California Flora. University of California Press, Berkeley, CA. 1681 pages.

Rydberg, Per Axel. 1917. Notes on Rosaceae--XI. Roses of California and Nevada. Bulletin of the Torrey Botanical Club 44: 65--84.

_______. 1918. Rosa. North American Flora 22(6): 483--533.

Watson, Sereno. 1885. XIV. Contributions to American Botany. 1. A history and revision of the roses of North America. Proceedings of the American Academy of Arts and Sciences 20: 324--352.

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