Panarctic Flora

320103-04 The Juncus triglumis aggregate J. albescens, J. triglumis

Geography: Circumpolar-alpine.

Notes: Elven and Murray: The two taxa within Juncus triglumis s. lat. have been treated as species (e.g., Porsild and Cody 1980), subspecies (e.g., Tolmachev 1963; Hultén 1968a; Elven 1994; Cody 1996; Elven et al. 2005; Kirschner et al. 2002b), or varieties (e.g., Brooks and Clemants 2000). Some authors report J. triglumis and J. albescens to be largely sympatric and difficult to keep apart in several regions (e.g., Kirschner et al. 2002b), whereas others report comparatively clear-cut morphological differences (e.g., Brooks and Clemants 2000). Main diffences are: subtending bract short and obtuse in J. triglumis s. str. vs. longer, acute or with an extended plate in J. albescens; tepals short and obtuse and not nearly reaching the top of the mature fruit vs. long and acutish and often reaching the top; tepals not turning whitish vs. often turning whitish; and fruit tapering beneath the beak vs. more or less truncate. Comparing plants from mainland Europe (J. triglumis s. str.) with ones from Greenland and eastern Canada (J. albescens), these differences hold nicely, but not as well when comparing with plants from northwestern North America and northeastern Asia where the variation may be less discontinuous. However, we have seen no plants closely approaching European J. triglumis morphologically from these regions. The variation within J. albescens may be larger than presumed from a study of eastern North American specimens alone. We are not convinced that the sympatry is as extensive as proposed by, e.g., Kirschner et al. (2002b).

There may be a difference in chromosome number levels, a possible explanation of the co-occurrence as reported by Yurtsev (in comment) for northeastern Asia: "In many parts of Chukotka tundra (on base-saturated soils) both taxa are sympatric, which is true even of the only locality in the very center of Wrangel Island where J. triglumis s. lat. occurs". However, the chromosome evidence is inconclusive, and we would rather assign the plants we have seen from Chukotka within J. albescens. We have confirmed plants clearly conforming to J. triglumis (as typified) from mainland Europe, central and southern Siberia, and the southern Russian Far East; plants conforming to J. albescens from northern Siberia, the northern Russian Far East, North America, Greenland, and Svalbard. We have entered the two as species and with the ranges as suggested above, with some question marks due to lack of material for inspection. Our reason for choice of species rank is the absence of transitional forms in areas of (some) contact.