10 BRITTONIA [VOL. 57 FIG. 7. Morphology and micromorphology <strong>of</strong> achenes. A. <strong>Polygonum</strong> sawatchense subsp. sawatchense. B. P. sawatchense subsp. oblivium. C. P. tenue. D. P. <strong>douglasii</strong>. E. P. majus. F. P. spergulariiforme. G. P. austiniae. H. P. engelmannii. I. P. gabrielae. J. P. utahense. Scale bar � 1 mm for all figures except Figure 7D where scale bar is 100 �m.
2005] COSTEA & TARDIF: POLYGONUM DOUGLASII COMPLEX 11 Small, P. spergulariiforme Meisn. ex Small, P. majus Meisn., P. nuttallii Small, and P. austiniae Greene. He justified <strong>the</strong>se new combinations by <strong>the</strong> intermediate patterns <strong>of</strong> variation between some <strong>of</strong> <strong>the</strong> taxa. A sixth species, P. engelmannii Greene was put in synonymy under P. <strong>douglasii</strong> based on a previous observation that <strong>the</strong> two taxa are closely related (Hitchcock, 1964) and because ‘‘<strong>the</strong> distinction <strong>of</strong> <strong>the</strong>se two taxa is not always clear’’ (Kartesz & Gandhi, 1990). The majority <strong>of</strong> collections annotated as ‘‘intermediates’’ by Hickman (in CAS, DS, JEPS, RSA, and UC) are ei<strong>the</strong>r between ‘‘P. <strong>douglasii</strong> subsp. <strong>douglasii</strong> and subsp. johnstonii’’ (P. <strong>douglasii</strong> and P. sawatchense subsp. sawatchense, respectively) or between P. <strong>douglasii</strong> and P. spergulariiforme. Most <strong>of</strong> <strong>the</strong>se ‘‘intermediates’’ are, in our opinion, within <strong>the</strong> range <strong>of</strong> variation <strong>of</strong> each taxon, which has been poorly understood. In <strong>the</strong> first case, plants regarded by Hickman as intermediates between ‘‘subsp. <strong>douglasii</strong> and subsp. johnstonii’’ are ei<strong>the</strong>r P. <strong>douglasii</strong> or P. sawatchense subsp. sawatchense (Costea & Tardif, 2003a). In <strong>the</strong> second case, most <strong>of</strong> <strong>the</strong> plants considered by Hickman intermediates between P. <strong>douglasii</strong> and P. spergulariiforme belong, in our opinion, to P. majus. In most <strong>of</strong> <strong>the</strong> situations encountered, plants can be assigned to each species using qualitative or quantitative characters. Hybridization may have played a role in <strong>the</strong> evolution <strong>of</strong> this group <strong>of</strong> species, but <strong>the</strong> relatively low levels <strong>of</strong> introgression observed do not warrant <strong>the</strong>ir combination in a single species. The close relationship between <strong>the</strong>se taxa does not justify a cumbersome species concept <strong>of</strong> P. <strong>douglasii</strong>, to which should also be added following <strong>the</strong> same criterion even more species: P. minimum, P. cascadense, and P. utahense, as well as a previously undescribed species, P. gabrielae. This is not <strong>the</strong> same situation within <strong>the</strong> P. aviculare L. complex, where taxa are linked by a continuum transition <strong>of</strong> variation patterns, which makes <strong>the</strong>ir recognition at species rank unrealistic (Costea & Tardif, 2003b). Consequently, a species concept closer to that <strong>of</strong> Small (1895) and Hitchcock (1964) is followed here (see also <strong>the</strong> discussions under each species). This group <strong>of</strong> species is probably monophyletic and may be worth recognizing as a subsection <strong>of</strong> <strong>the</strong> section Duravia (emended by Hedberg, 1946). Hickman (1984) elevated Duravia to <strong>the</strong> subgenus rank and separated from it a new section, Monticola, in which he included <strong>the</strong> species <strong>of</strong> <strong>the</strong> P. <strong>douglasii</strong> and P. polygaloides complexes. According to this classification, section Duravia incorporates species from lowland and foothill locations, with leaves not obviously jointed to ocreae, linear, 3-nerved (rarely 1-nerved), mucronate apex and styles separate, hardened, and persistent at least at <strong>the</strong> base. In contrast, Monticola includes species from montane areas, with leaves obviously jointed to ocreae, apex not mucronate, at least lowest leaves lanceolate to round and styles, that are fused at base and nei<strong>the</strong>r hardened nor persistent (Hickman, 1984). However, we found a considerable overlap between Duravia and Monticola in <strong>the</strong>se characters. Additionally, some species from Duravia cannot be classified in any <strong>of</strong> <strong>the</strong> two sections (e.g., P. shastense Brewer ex A. Gray and P. paronychia Cham. & Schlecht.). Therefore, in this study, section Duravia is interpreted to include section Monticola. The latter section, circumscribed here to include only <strong>the</strong> species <strong>of</strong> P. <strong>douglasii</strong> complex, may be accepted after fur<strong>the</strong>r study as a subsection <strong>of</strong> Duravia. Some authors (Ronse Decraene & Akeroyd, 1988; Ronse Decraene et al., 2000) suggested that even section Duravia is artificial because <strong>of</strong> <strong>the</strong> partial overlap in floral and fruit characters between some <strong>of</strong> its species and <strong>the</strong> section <strong>Polygonum</strong>. Although section Duravia is heterogeneous and shares some features with section <strong>Polygonum</strong> (Ronse Decraene & Akeroyd, 1988; Ronse Decraene et al., 2000), <strong>the</strong> morphology <strong>of</strong> stems, color <strong>of</strong> an<strong>the</strong>rs, venation pattern, structure <strong>of</strong> petioles (Haraldson, 1978), and morphology <strong>of</strong> pollen (Hedberg, 1946) clearly separates <strong>the</strong> two sections.
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