Polytrichadelphus lyallii Mitt., Jour. Linn. Soc. Bot. 8: 49. f. 1-6. 1865.
Polytrichum lyallii (Mitt.) Kindb., Revue Bryol. 21: 38. 1894.
An idea of the distribution of Polytrichastrum and Polytrichum may be had from Brotherus' (19251 synopsis of Poii/iric/iwm. Herzog's (1926) argument that the "Massenentwicklung" of the genus Polytrichum indicates a boreal origin, counterbalanced by the obvious affinity between Polytrichum and the Southern
Hemisphere genera, Polytrichadelphus and Dawsonia. Both Polytrichastrum and
Polytnchum occur in the Southern, as well as in the Northern Hemisphere.
The oldest fossil linked with the Polytrichaceae, Muscites polytrichaceus
Renault & Zeiller, dates from the Stephanian (Upper Upper Carboniferous) of
France. Walton (1928) called attention to the "relatively unimportant fact" that
the leaves of this plant are not uniformly distributed along the stem, but are
disposed in a way which suggests the successive inflorescences of Polytrichum
male shoots. The next most recent reputed fossil Polytrichaceae date from the
mid-Tertiary! No fossil mosses resembling the Polytrichaceae were recorded from
the Southern Hemisphere by Jovet-Ast (1967).
Polytrichum need not be regarded as an outgrowth of Polytrichastrum. I look
upon Polytrichastrum, Polytrichum, Polytrichadelphus and Dawsonia as the surviving
descendants of an ancient polytrichoid alliance, probably of world-wide
distribution. Polytrichastrum retains most of the generalized features of this
ancestral taxon. There is reason to believe that this same stock was not far
removed from the common ancestor of the Polytrichaceae as a whole (cf the
concluding remarks at the end of this part).