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

Fig. 24,41,42,65, 70-76.

Type: Polytrichum hercynicum [(Ehrhart, Beür. 1: 191. 1787. Catharineae) Hedwig, Descr. 1: 40. 1787.] Hedwig, Sp. Muse. 94. 1801. type. cons, propos.

Psilopilum is often cited as a moss genus with a "bipolar" distribution (e.g., Herzog, 1926). Psilopilum laevigatum (Wahl.) Lindb. and the closely related P. cavifolium (Wilson) I. Hagen occur at high latitudes in the Northern Hemisphere. The remaining species of the genus are widely distributed in the Southern Hemisphere, but only two species (P. trichodon (Hook. f. & Wilson) Mitt. [ = P. antarcticum (C. Müll.) Paris] whose northern limit is the Colombian Andes, and P mexicanum G. L. Smith, known only from the type locality in Tlaxcala, Mexico) occur north of the Equator. Considered independently, the distribution of the austral group of species (Fig. 77) conforms to a modified Antarctic radiant pattern, and it should not be surprising, therefore, that there are morphological dissimilarities between them and the two arctic, circumpolar species. The peristomes of P laevigatum and P cavifolium consist of stout, linear, blunt, closely approximated teeth (Fig. 78), whereas the peristome of the austral species is characterized by distant, tapering, rather sharp-pointed teeth (Fig. 79).

The austral species of Psilopilum have a number of features in common, although they vary considerably in the distribution of adaxial lamellae on the leaf. Most of the species bear papillae on the margins of the lamellae, and usually over the rest of the leaf surface as well. The stomata are sunk below the surface of the exothecium in most species, and are overarched by the swollen surrounding cells, which form a conspicuous band around the base of the capsule.

In an earlier, general discussion of the lamellae, I traced the progressive reduction in the surface of the leaf occupied by adaxial lamellae, beginning with a type represented by Psilopilum australe (Hook. f. & Wilson) Mitt., and ending with a unistratose lamina, and the lamellae restricted to the narrow nerve, as in Oligotrichum. In m y opinion, many if not all of the present day species of Oligotrichum have been derived in this manner. If its broad, bistratose lamina bore lamellae, O. tenuirostre (Hook.) Jaeger, of New Zealand, would certainly have been referred to Psilopilum. Moreover, the peristomes of most Southern Hemisphere Oligotrichum species [e.g., O. carnalicidatum (Hook. & Arnott) Mitt.] are of the austral Psilopilum type described above.

In other species of Oligotrichum [e.g., O. aligerum Mitt., O. parallelum (Mitt.) Kindb., and the type species of the genus, O. hercynicum (Hedw.) Lam. & D C ] the peristome teeth are compound, the stomata tend not to be restricted to the base of the capsule, and the leaves produce abaxial, as well as adaxial lamellae. Oligotrichum parallelum and O. aligerum are southern Beringia radiants (cf Hulten, 1937), although O. aligerum has a close relative in the Philippines, Java, and Sumatra in O. javanicum (Hampe) Dozy & Molk., and in the Himalayas in O. falcifolium (Griff.) G. L. Smith. Oligotrichum aligerum itself is present in Mexico, Jamaica, and Costa Rica. Oligotrichum falcatum Steere, known from arctic Alaska and Greenland, differs from O. hercynicum in its falcate leaves, and its serrulate lamellae. In the later respect, it approaches the Himalayan 0. semilamellatum (Hook, f.) Mitt. The northern centers of these taxa, and the circumboreal range of O. hercynicum are in marked contrast to the distribution of the Oligotrichum species akin to the austral Psilopila. Of these, only O. erosum (Hampe) Lindb. extends north of the Equator, in Colombia. Oligotrichum is represented in Malaysia by two distantly related species, which evidently entered the area from opposite directions: O. javanicum from the north via the Formosa-Luzon and the Sumatran migratory tracks, and Oligotrichum novae-guineae (E. Bartram) G. L. Smith, comb. nov. (Basionym: Atrichum novae-guineae E. Bartram, Revue Bryol. Lichenol. 30: 206. 1961. Isotype, CAN!) from the south via the Papuan migratory track (cf van Steenis, 1934). The New Guinean species resembles O. tenuirostre, of New Zealand, except for its unistratose leaf lamina.

The type elements of both Psilopilum and Oligotrichum appear to be more closely related to one another than to many of the species in their respective genera, and these species, in turn, are evidently more closely related to one another than to the type species of the genus in which they now reside. According to this view, species such as Psilopilum australe represent the primitive type, from which have been derived the other austral species of Psilopilum. as well as the genus Oligotrichum. Psilopilum laevigatum and P cavifolium, on the other hand, originated at high latitudes in the Northern Ilemisjihere, and are prolnibiy derived from Oligotrichum, fiom which they are readily distinguishable by their distinctive peristome. Assuming this to be true, the separation of the arctic, type element of Psilopihim from its alleged congeners in the Southern Hemisjihere is in order: