A biosystematic study of the Carduus nutans complex in Canada

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Abstract
The Carduus nutans L. complex in North America has been treated either as one species with four subspecies (ssp. nutans, ssp. leiophyllus (Petrovic) Stoj. & Stef., ssp. macrolepis (Peterm.) Kazmi, and ssp. macrocephalus (Desf.) Nyman) or as three species: Carduus nutans with two subspecies (ssp. nutans and ssp. macrolepis), C. thoermeri Weinm., and C. macrocephalus Desf. A biosystematic study of this complex, including morphological, flavonoid, and isozyme analyses, of 19 populations, was conducted to clarify the taxonomy of this complex in Canada. Both the morphological and flavonoid analyses clearly indicate the existence of only two closely related groups of taxa referable to ssp. nutans and ssp. leiophyllus. The classificatory discriminant analysis indicated correct classification rates of individuals of 93.6% and 96.0% for ssp. nutans and ssp. leiophyllus, respectively. Each taxon has a distinct flavonoid profile. Given the high mean genetic identity value (ī = 0.93) between the two taxa in the complex, and the estimates of genetic variability obtained, the taxa are best treated at the subspecific level, as ssp. nutans and ssp. leiophyllus.

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