Panarctic Flora

320105-06 The Juncus castaneus aggregate J. castaneus, J. leucochlamys

Geography: Circumpolar-alpine.

Notes: Elven, Murray, and Solstad: Russian authors have accepted Juncus castaneus and J. leucochlamys as two species and J. leucochlamys to largely or entirely replace J. castaneus in northeastern Asia (e.g., Tolmachev 1963; Novikov 1985; Egorova PAF proposal). For Alaska, Hultén (1943b: 428) first accepted two species but later (Hultén 1968b: 31) - after investigating a larger material - changed his opinion to subspecies because they seemed to intergrade morphologically. Brooks and Clemants (2000) synonymized J. leucochlamys with J. castaneus for North America.

We have inspected plants from North America, Greenland, northern Europe, and some from northern Asia (ALA, AMNH, CAN, ICEL, O, TRH, TROM), and have reached a conclusion that may explain the divergence between the Russian and North American treatments (Elven et al. 2010). We accept two species for the Checklist: J. castaneus and J. leucochlamys. We find all material we have inspected from northeastern Asia, North America, Greenland, and Svalbard to differ in some consistent features from the material from northern mainland Europe and northwestern Siberia: tepals longer and subequal in J. leucochlamys vs. shorter and the inner much shorter and subobtuse in J. castaneus s. str.; tepals and capsule of subequal length vs. tepals much shorter than capsule; capsule uniformly much longer in J. leucochlamys than in J. castaneus s. str. and tapering and distinctly beaked vs. abruptly narrowed and with a short beak. Other reported characters do not differentiate fully as reliably as those above: Long bracts are more typical of J. leucochlamys than of J. castaneus s. str.; inflorescences with several levels are more common in J. leucochlamys as are paler tepals and capsules, but dark and one-level inflorescences are common also in what we now accept as J. leucochlamys and several levels may occur in J. castaneus s. str.; leaf width does not separate even if some specimens of J. leucochlamys are conspicuously broad-leaved. Following our criteria, the two taxa become nearly allopatric.

The situation in Iceland is especially revealing. There, J. castaneus s. lat. occurs in two subareas, one in the northwest and another in the east, with a gap across central Iceland. All plants from the northwestern subarea belong to J. leucochlamys, those from the eastern to J. castaneus s. str., and without a single specimen showing transitional features (AMNH, ICEL).

Juncus castaneus s. str. is restricted to northern Europe (including eastern Iceland) and northwestern Siberia east to Taimyr, whereas the geographically major taxon is J. leucochlamys, distributed in northeastern Siberia eastwards from Taimyr, the Russian Far East, North America, Greenland, northwestern Iceland, and Svalbard. We have not yet seen intermediates in the inspected material. However, we have not seen much material from the possible meeting zone in northern Siberia. The problems of separation in North America (as discussed by Hultén 1968b) is then resolved as only one species is present. Our ranges of the two species deviate strongly from those mapped by Kirschner et al. (2002b, for two subspecies).