Phytologia (Dec2006) 88(3) 279 TAXONOMYAND NOMENCLATURE OF THE ERYSIMUM ASPERUM-E. CAPITATUMCOMPLEX (BRASSICACEAE) B. L. Turner Plant Resources Center The University ofTexas at Austin Austin, Texas 78712 [email protected] ABSTRACT The Erysimum aspei~um-capitatum complex includes a vast array of taxa in the western U.S.A. and Mexico, most ofthese bearing specific or infraspecific names, and all to some extent intergrading in regions of allopatry. These appear to be best treated as belonging to but a single species, Erysimum asperum, with two subspecies: subsp. asper-um, with but a single relatively well-marked var. asperum, this confined to the Great Plains Region of the central U.S.A., and subsp. capitatum ofthe higher, more western regions, the latter having an array of varietal names, the earliest being var. elatum, first proposed by Torrey in 1858. To accommodate the nomenclature of this overview, the following names are proposed: E. asperum subsp. capitatum (Douglas) B.L. Turner comb, and stat. nov., and E. a. var. lompocense (Rossbach) , B.L. Turner, comb. nov. KEY WORDS: Brassicaceae, Erysimum, E. asperum, E. capitatum, California. As noted by Al-Shehbaz (1988) and Rollins (1993), Erysimum is a genus of about 200 species largely confined to the Northern Hemisphere. Most of its species are confined to Eastern Europe and southwestern Asia. Rollins recognized 17 species as native to North America, these largely confined to the western United States. He also provided a tortuous key to the American taxa, based upon considerable herbarium and field experience. Among American species, the most difficult taxa belong to the Erysimum asperum-E. capitatum complex of the western United States, which is the subject of the present contribution. 280 Phytologia (Dec2006) 88(3) In his treatment of the complex, Rollins recognized both E. asperum and E. capitatitm, distinguishing between these in his key lead 10/10, as follows: 10. Siliques rigidly spreading nearly at right angles to the rachis, tetragonal; valves strongly ribbed, densely pubescent between the ribs and sparsely pubescent on the ribs giving a striped appearance E. asperum 10. Siliques divaricately ascending to erect; valves not strongly ribbed, more or less evenly pubescent, not markedly striped E. capitatum et al. The principal distinction between the two taxa is clearly that of silique divergence, which in mature fruiting material is readily seen. In my opinion, other than divergence, the valve distinctions called to the fore by Rollins are exceedingly arbitrary. At least these are not readily apparent in the large numberofpressed specimens I have examined. Nevertheless, E. asperum (the earliestname forthe duo), does exist as a well defined morphogeographical entity ofthe Great Plains ofthe central United States (Figs. 1, 2), readily recognized by its smaller habit, spreading siliques, and confinement to grassland habitats. Westwards and/or upslope, E. asperum grades into the largely allopatric E. capitatum, either as a result of extant or near extant hybridization (secondary intergradation) and/or ancestral in situ divergence (primary intergradation) of the two taxa concerned. Intergradation of the latter type (allopatric introgression) is usually much more gradual and more difficult to detect than the former (sympatric hybridization), as well noted by Anderson (1953). Weber (1990) noted thatbothE. asperum andE. capitatum occurin Colorado and that the former hybridizes with the latter "along the base ofthe foothills." He further notes that E. capitatum has "siliques green and almost glabrous, ascending, usually nearly parallel to the stem, although the pedicels may spread widely." He also added that E. capitatum is "very common and extremely variable." Indeed, intergrades between the two taxa can be found (or inferred) throughout the region ofallopatric and/or sympatric contact, this often 1 Phytologia (Dec2006) 88(3) 28 perceived in populations relatively remote from regions of immediate contact, suggesting long-term introgression, this supporting the view that the intergradation is ofaprimary nature. Regardless, numerous floristic workers have been confounded by the two taxa, some treating these as but a single widespread variable species (e.g., Davis 1952; Hitchcock and Cronquist 1973; Harrington 1979 [who noted that E. asperum included elements ofthe E. capitation complex and that its siliques may be "ascending or rarely divaricate."]; Walsh et al. 1987; Albee et al. 1988; Scott 1995 [ who recognized but a single species, E. asperum, under this listing 22 specific names in synonymy, this perhaps unrivaled among any other plant species ofthe western U.S.A.]). Even within the boundaries of California Hoover (1970), in his discussion ofE. capitatum, E. moniliforme and E. occidentale, noted that "Herbarium specimens ofboth E. occidentale and E. asperum can be found which differ from individuals of E. moniliforme in no outwardly visible way. I suspect that, after adequate studies of the plants in all their habitats and in cultivation, these plants will ultimately be included inE. asperum.'" Nevertheless, Price (1993), in his treatment of Californian Erysimum for the Jepson Manual, excluded E. asperum from that state, but he did recognize E. capitatum (albeit with at least 4 subspecies, and yet other specific segregates such as E.franciscanum, E. sujfrutescens, andE. insulare). Reveal (1972) summed up the controversy over the competing names thusly: Erysimum asperum is a widespread and highly variable species that is composed of several weakly defined varieties. The type of the species comes from the Great Plains and has more or less spreading fruits. The western United States material with yellow flowers and erect fruits should be called var. purshii. Hitchcock (1964) was unable to determine which name should be applied to this phase, being unaware of Durand's publication. In most western floras, this phase has been called E. capitatum (Doug, ex 282 Phytologia (Dec2006) 88(3) Hook.) Greene, although Welsh et al. (1965) call this plant simply E. asperwn. Those specimens with orangish or reddish flowers from the southern Rocky Mountains and high mountains of Utah should be called E. asperwn var. amoenum (Greene) Reveal, comb. & stat. nov., based on Cheiranthns nivalis var. amoenus Greene, Pittonia 3: 137. 1896. Holmgren (1959) and Welsh et al. (1965) have called this phase E. wheeleri Rothr. Similar plants occur sporadically in the Pacific Northwest but appear to represent another kind as yet undescribed (Hitchcock 1964), while those of the southern Coast Range of California are called E. asperwn var. stellatum J. T. Howell. Reveal briefly outlined the nomenclatural consequences of a widespread highly variable E. asperwn (including E. capitatum, this relegated to synonymy under E. asperwn var. purshii), he apparently was unaware ofthe earlier varietal name, E. asperwn var elatwn (Nutt. & ex Torr. Gray) Torr., a combination first published in 1858 (2 years before E. asperwn var. purshii). The type ofE. a. var. elatum (= E. elatwn Nutt.) is from northwestern Oregon , reportedly from along the Wahlamet (= Willamet) River, first collected by Nuttall himself. Rollins (1993) included this variety within his concept of£. capitatum var. capitatum. Clearly though, if E. capitatum is treated within an expanded E. asperwn, such as I do for the state of Texas, the earliest legitimate varietal name for the E. capitatum complex (sensu lato) is E. asperum var. elatum. My taxonomic account of the E. asperum-E. capitatum complex canbe summarized as follows: Erysimum asperum comprises two subspecies: 1.) subsp. asperum, which is composed ofa single, more or less well defined var. asperwn, largely confined to the prairie lands ofthe central U.S.A.; and 2.) subsp. capitatum, which is largely confined to the more montane regions ofthe western U.S.A., Canada, and Mexico, although occasional populations occur in the more forested regions ofthe eastern U.S.A., where perhaps introduced. Within the subsp. capitatum numerous forms and populations exist, some seemingly worthy of varietal recognition as espousedbythe criteria ofTurnerandNesom (2000). Phytologia (Dec2006) 88(3) 283 Price (1993), in his treatment ofthe genusErysimum forCalifornia, did notrecognize E. asperum, but instead, treated all ofthe taxa relating to this as E. capitatum. Within the latter he recognized four subspecies, as follows: 1.) subsp. angustatum (E. Greene) R.A. Price [= E.capitatum var. angustatum (E. Greene) Rossbach]; 2.) a typical E. c. subsp. capitatum [including E. asperum var. stellatum J. Howell, E. capitatum var. bealianum (Jeps.) Rossbach, E. argillosum (E. Greene) Rydb., and E. moniliforme Eastw.]; 3.) subsp. lompocense (Rossbach) R.A. Price [= E. capitatum var. lompocense (Rossbach) Kartez = E. suffrutescens (Abrams) Rossbach var. lompocense}; and 4.) subsp. perenne (Cov.) R.A. Price [= E. perenne Coville) Abrams; and E. capitatum var. perenne (S. Wats, ex Cov.) R.J. Davis]. Unfortunately, as of this writing none of the aforementioned subspecies has been formalized. Price noted that the four subspecies (or varieties) intergrade locally with peripheral subspecies, including alsoE. insulare ssp. suffrutescens. This being so, I am inclined to recognize the taxa concerned as varieties within the largersubspecific category, capitatum ofErysimum asperum. The formal nomenclature for the Californian taxa follows: Erysimum asperum (Nutt.) DC, Syst. Veg. 2: 505. 1821. Basedon Cheiranthes asperum Nutt., Gen. N. Amer. PI. 2: 69. 1818. Erysimum asperum (Nutt.) DC. subsp. asperum Price (1993) proposed, butdid not make formal, the rank ofsubsp. capitatum within his concept ofE. capitatum. Erysimum asperum subsp. capitatum (Douglas) B.L. Turner, comb. & stat. nov., Basedon Cheiranthus capitatus Douglas, in Hook. Fl Bor. Am. 1:38. 1829. Erysimum asperum var. angustatum (Rydb.) B. Boivin, Phytologia 16:298. 1968. Erysimum asperum var. elatum (Nutt.) Torrey, Pacific Railroad Report 7, Pt. 3. 1858. This is the earliest varietal name within the subsp. capitatum, havingpriority overE. asperum var. 284 Phytologia (Dec 2006) 88(3) capitation (Douglas ex Hook.) B. Boivin, Naturaliste Canad. 94: 646. 1972. Erysimum asperum var. lompocense (Rossbach) B.L. Turner, comb. nov. Based uponErysimumsuffrutescens var. lompocenseRossbach, Aliso4: 123. 1958. Erysimum asperum var. perenne S. Watson ex Coville, Proc. Biol. Soc. Washington: 7: 70. 1892. ACKNOWLEDGMENTS I am grateful to Guy Nesom forreviewing the manuscript, and for his helpful comments. Figures 1 and 2 are compiled from the distribution ofE. asperum as shown in the Atlas ofthe Flora ofthe Great Plains (1977: Iowa State Univ. Press) and specimens at LL, SRSC, and TEX; intermediates between the two taxaare not indicated in Fig. 2, but exist in the southern Panhandle region ofTexas, as also noted by Rollins (1993). LITERATURE CITED Abrams, L. 1944. Erysimum, in Illustrated Flora ofthe Pacific States 2:318. Albee, B.J., L.M. Schultz, and S. Goodrich. 1988. Erysimum, in Utah MuseumNatural Hist., Occasional Publ. 7: 168. Al-Shehbaz, LA. 1988. The generaofAnchonieae (Hesperideae) (Cruciferae; Brassicaceae) in the southeastern United States. J. ArnoldArbor. 69: 193-212. Anderson, E.A 1953. Introgressive Hybridization. Wiley Press, New York. Davis, R.J. 1952. FloraofIdaho. W. C. Brown Co. Press, Dubuque, Iowa Harrington, H.D. 1954. Manual ofthe plants ofColorado. Sage Books, Denver Phytologia (Dec2006) 88(3) 285 Hitchcock, C.L. and A. Cronquist. 1973. Flora ofthe Pacific Northwest. Univ. ofWashington Press, Seattle. Hoover, R.F. 1970. The VascularPlants ofSan Luis Obispo County, California. Univ. ofCalifornia Press, Berkeley. Price, R.A. 1993. Erysimum, in the Jepson Manual. Univ. ofCalifornia Press, Berkeley. Reveal, J.L. 1972. Comments on two names in an earlyUtah flora. Great Basin Naturalist 32: 221-222. Rollins, R.C. 1993. The CruciferaeofContinental North America. Stanford Univ. Press, California. Scott, R.W. 1995. Alpine Flora ofthe Rocky Mountains (The Middle Rockies 1: 247.). Univ. ofUtah Press, Salt LakeCity. Turner, B.L. and G.L. Nesom. 2000. Use ofvariety and subspecies and new varietal combinations forStyraxplatanifolius (Styracaceae). Sida 19: 257-262. Weber, W.A. 1990. Colorado Flora: eastern slope. Univ. Press of Colorado, Boulder Weber, W.A. and R.C. Wittman. 1996. Colorado Flora: Western Slope, Univ. ofColoradoPress Welsh, etal. 1987. A Utah Flora. Erysimum, in Great BasinNaturalist 9: 268. 286 Phytologia (Dec2006) 88(3) i rl"~ Flo.<DistributionofErysimumasperumsubsp.asperum(opencircles^ subsp.elatum(closedcircles;Intermediates(halfcircle). Phytologia (Dec2006) 88(3) 287 o var.asperum • var.datum Fig.2.Erysimumasperum(InTexas);intermediatesnotshown.