Monographs Details: Polytrichastrum lyallii (Mitt.) G.L.S.Merr.
Authority: Smith, Gary L. 1971. Conspectus of the genera of Polytrichaceae. Mem. New York Bot. Gard. 21: 1-83.

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).