Holotype: Philocrya aspera I. Hagen i\: C. Jensen, Medd. Gr0nland 15: 388. f.1-9. 1898.
Philocrya aspera I. Hagen & C. Jensen is a rare, high arctic species, which up
to now has been collected in only a few, very widely separated localities. Its
northernmost outpost is in Peary Land, northern Greenland (Holmen, 1960), and
its southernmost known localities are in Siberia, shghtly south of 65° N (Smirnova,
1958). The history of the species and the question of its relationshijjs were discussed
in some detail by Steere (1956).
Salmon (1901) advocated the transfer of Philocrya aspera to Lyellia, without
making the formal combination; Frye (1937) later supplied the same. While it
is true that Philocrya has never been collected with capsules, and that its distribution,
as presently known, is quite discontinuous with that of Lyellia (Fig. 90), the
gametophytes of the two genera agree in virtually all respects. The leaves of
Philocrya produce a unique terminal capillary bristle (Fig. 84), and are not as
contorted in the dry condition as are those of Lyellia, but these are specific, rather
than generic distinctions.
The highly disjunctive range of the genus Lyellia is characteristic of plants which were formerly widespread in the Northern Hemisphere, and which survived the Pleistocene glaciations in isolated refugia. Lyellia aspera is now restricted to these areas of relictual survival in Greenland, arctic Canada, Alaska and Siberia, being unable, because of severe limitation of its ecotypic amplitude, to attain more widespread distribution in postglacial times (cf Hulten, 1937). The other Lyellia species represent the southernmost portion of the former distribution of the genus, isolated by the effects of glaciation, and by the vast arid plateau to the north, whose climate was only intensified during the interglacial periods.