Monographs Details: Polytrichadelphus
Authority: Smith, Gary L. 1971. Conspectus of the genera of Polytrichaceae. Mem. New York Bot. Gard. 21: 1-83.
Scientific Name:Polytrichadelphus

Fig. 15, 53-58.

Type: Polytrichum magellanicum [L. f.] Hedw.

Catharinea sect Polytrichadelphus C. Müll., Syn. 1: 201. 1848.

Lectotype: Polytrichum magellanicum [Linnaeus f., Suppl. PI. 449. 1781.] Hedwig, Sp. Muse. 101. 1801.

Polytrichum subg Cyphoma Hooker f. & Wilson, Fl. Nov. Zel. 2: 95. 1854.

Holotype: Polytrichum magellanicum [L. f.] Hedw.

The genus Polytrichadelphus is credited with 21 species by Brotherus (1925), and 28 by van der Wijk et al. (1967), most of which occur in the northern Andes. The genus also has representatives in Costa Rica, southeastern Brazil, southern Chile, New Zealand, Tasmania and Australia, and N e w Guinea (Fig. 59). Based on m y preliminary study of the genus the number of species seems inflated. One of the species, P. integrifolius C. Müll. ex E. G. Britton (Holotype, NY!) is not a Polytrichadelphus, but a form of Polytrichum juniperinum. The western North American P. lyallii Mitt, is better referred to the genus Polytrichastrum (cf the discussion under that genus).

The numerous species described from Central America and northern South America probably represent a secondary center of speciation, with an ultimate origin to the south. Polytrichadelphus semiangulatus (Brid.) Mitt., the representative of the genus in southeastern Brazil, is closely related to the northern Andean species.

The austral element is usually regarded as a single species, P. magellanicus (Hedw.) Mitt, [incl P horridus Mitt, and P. robustus (Lindb.) Broth.]. In my opinion, the Polytrichadelphus of New Zealand, Tasmania and southeastern Australia should be treated as a distinct species, Polytrichadelphus innovans (C. Müll.) Jaeger (Isotype, NY!). Compared with the American P. magellanicus, the plants are smaller and more slender, with shorter, subsecund leaves. The leaf sheath is broader, with more pronounced shoulders, and the teeth on the margin of the blade less well developed. The capsules are smaller and paler, with more delicate walls, and as a rule, the peristome arises from a high, fluted basal membrane, in contrast to the usually low basal membrane of the American plant. With the segregation of P. innovans, the distribution of P. magellanicus is limited to Juan Fernandez, Chile south of about latitude 40°S, the Fuegian region, Falklands, and Tristan da Cunha. Polytrichadelphus archboldii E. Bartr. (Holotype, FH!), of New Guinea, is closely allied to P innovans, but has a long, finely attenuate awn at the tips of the leaves. I have seen no material of P papuanus E. Bartr., described from Goodenough Island, of the Entrecasteaux group.

By analogy drawn from Hulten's work on the origins of distribution patterns of arctic and boreal plants (1937), we may use the term Antarctic radiants for those taxa whose areas appear to center along the Pacific coast of the continent of Antarctica, and radiate toward New Zealand, Tasmania, and Australia on the one hand, and southern South America on the other (the circum-South Pacific distributional areas of van Steenis, 1953). Fossil floras indicate that during the greater part of the Tertiary, and perhaps earlier, the Pacific coast of Antarctica was almost certainly covered by forests which were similar to the present forests of New Zealand and southem Chile.

There is abundant direct, as well as indirect evidence that altered climatic conditions had led to the radiation of elements of this characteristic vegetation into lower latitudes even before the Pleistocene. O n the basis of fossil pollens, the present day Malaysian distribution of Nothofagus, Phyllocladus, and Podocarpus (sect Dacrycarpus) is almost certainly a result of migration in late Pliocene to early Pleistocene times (Couper, 1960). The presence of Polytrichadelphus archboldii in New Guinea is undoubtedly a result of the same phenomenon, as is the present Malaysian distribution of the genus Dawsonia. The radiation of Polytrichadelphus into northern South America probably occurred at about the same time.

Unlike conditions in the Northern Hemisphere, the persistence of the Antarctic ice cap has largely prevented even the partial restoration of the preglacial range of the Antarctic radiants at higher latitudes. The modern, vicariant representatives of Polytrichadelphus in New Zealand and in southern South America are surviving fragments of what was once a single, widespread species.