Cirsium ochrocentrum subsp. martinii (Asteraceae), a New Subspecies of the Santa Fe Thistle from the Gila River Region of Arizona and New Mexico

Abstract

A morphological study of Cirsium ochrocentrum supports separation of the phenotype with red corollas of the upper Gila River drainage from typical materials with purple or white corollas from surrounding regions. This taxon shows intergradation and overlap of character distributions with typical populations and is recognized as a subspecies. Cirsium ochrocentrum subsp. martinii differs from the typical variety by its red corolla color, short style tips and spines, and generally shorter decurrence. The American thistle genus Cirsium, with over 140 species (Ownbey et al., 1975), is an important part of the North American flora. Although American thistles have been falsely maligned as aggressive weeds because of their Eurasian congeners (Lamp & McCarty, 1981), western thistles provide a vital, and sometimes obligate, food source for many animal species including goldfinches, hummingbirds, and crescent butterflies (Martin et al., 1951; Tilden & Smith, 1986). Despite the ecological importance of these plants, taxonomists have largely neglected thistles. Current thistle taxonomy has both a confusing number of synonyms and a multitude of undescribed phenotypes that merit taxonomic recognition. In this report, I describe one such unrecognized group. Ownbey and Hsi (1963) suggested that the redcorolla phenotype of the Santa Fe Thistle, Cirsium ochrocentrum, might warrant recognition at the subspecies or species level. Hsi (1960) proposed a new taxon based on materials from Arizona with red corollas but did not validate the name with a published description. Barlow (1992) studied variation within the C. ochrocentrum group and showed that the red-flowered phenotype, which is found in the Gila River drainage of southeastern Arizona and southwestern New Mexico, was separable from the normally purple-flowered populations of the Rio Grande, Great Plains, Trans-Pecos, and Colorado Plateau. A summary of that analysis and the resulting description is presented here. METHODS AND MATERIALS Twelve morphological characters were measured on field-collected specimens from 56 populations (Fig. 1). Voucher specimens are deposited at UNM. The morphological characters used in this analysis were terminal leaf spine length, decurrence length, leaf length, corolla tube length, corolla throat length, corolla lobe length, style tip length, anther appendage tip length, anther appendage body length, pappus length, phyllary length, and phyllary spine length. Each population was represented by 1 to 18 specimens, and each floral character was represented by the average of 10 measurements per plant. This data set and the characters are fully described in Barlow (1992). A canonical discriminant analysis (CDA), using population averages, was used to graphically portray the distinctiveness of the red-corolla populations of the Gila River drainage from the typical Rio Grande valley purple-corolla populations. A third group, consisting of specimens from geographically intermediate populations with intermediate colors, was included to both verify their intermediacy in other character states and to offset the polarization of a CDA with only two taxa. Individuals were assigned to one of these three groups for this analysis. Discriminant analysis gives a linear combination of characters that best describes the classification. Ninety-five percent probability ellipses for the variance of each population were calculated. In a second analysis, 65 purple-corolla specimens from the upper Rio Grande Valley near the type locality of the typical subspecies were compared with 49 red-flowered specimens from Catron County, New Mexico, in a Kruskal-Wallis non-parametric comparison of the means. Statistical analysis was performed with NPAR1WAY, CANDISC, and IML procedures of the Statistical Analysis System (SAS Institute, 1989). Two hundred twelve herbarium specimens of Cirsium ochrocentrum were examined. NovoN 9: 318-322. 1999. This content downloaded from 157.55.39.83 on Sun, 09 Oct 2016 05:11:17 UTC All use subject to http://about.jstor.org/terms Volume 9, Number 3 1999 Barlow-Irick Cirsium ochrocentrum subsp. martinii 319 1180W 1030W 380N 38 N Nevada _.ta rado 10 1I O I California Arizona exlo ~~?? ooo