A Re-Evaluation of Orthotrichum euryphyllum

Abstract

Orthotrichum euryphyllum Vent. is distinct from Orthotrichum rivulare Turn. and O. sprucei Mont. It includes as a synonym O. epapillosum Lawt. & Herm., and is a species of springs and streamheads on volcanic plateaus in the semi-desert areas of Washington, Oregon, and northeastern California. In contrast, Orthotrichum rivulare is found in stream courses mostly in humid to perhumid, near-coastal areas. In addition to this radically different ecology, Orthotrichum euryphyllum has morphologic features that place it close to the European O. sprucei from which, however, it differs in cucullate leaf apices; strong costa often sinuose distally; and tighter, taller tufts. Compared with Orthotrichum rivulare, O. euryphyllum has larger cells; leaves that are elliptic-lanceolate without a clear distinction between an ovate base and a ligulate limb; leaf cells that are smooth or nearly so; a more gracile costal transverse-section; and entire leaf margins whose apices are abaxially quite cucullate. The Orthotrichum rivulare complex has been known to include the three species O. rivulare Turn., O. sprucei Mont., and O. euryphyllum Vent. All three taxa were listed for North America by Grout (1935), but Lawton (1971) and Vitt (1973) agreed in reducing Orthotrichum euryphyllum to a synonym of O. rivulare, and in correcting misidentifications that had assigned the European Orthotrichum sprucei to the western United States. This acceptance of only a single North American species in the Orthotrichum rivulare complex led to the description of a new species, O. epapillosum by Lawton and Hermann (1973) on the basis of a collection jointly made by E J. Hermann and D. H. Norris in the semi-desert country of northeastern California. Dale H. Vitt, on a number of occasions, both in personal conversation and in publication (see Vitt 1991), has expressed the view that Orthotrichum epapillosum is merely a dry morphotype of O. His view was followed without discussion by Lewinsky (1993). As one of the collectors of the original specimen of Orthotrichum epapillosum, D. H. Norris soon became aware of the almost constant presence of the species on rocks near springs that head small rivulets on volcanic plateaus in semi-desert areas of northeastern California. In contrast, Orthotrichum rivulare in California is almost exclusively a plant occurring in the more humid areas west of the Cascades, and it there occurs on occasionally flooded rocks and tree bases in riverine corridors. The tight reddish-brown cushions of Orthotrichum epapillosum are immediately recognizable even from a distance, and these cushions have no field resemblance to the loose and high tufts or cushions of O. rivulare that are blackish basally, but rich green in the younger parts. Skepticism concerning the synonymy of Orthotrichum epapillosum with O. rivulare led to careful microscopic study, and to collaboration with J. Lewinsky-Haapasaari in assessment of this taxon. We noted the markedly larger laminal cells of Orthotrichum epapillosum, and we observed the cucullate effect achieved by the apical recurvature of its entire-margined leaves. Vitt (1973) mentioned these same features in Orthotrichum euryphyllum, but he reduced the latter species to synonymy on the basis that its characters intergrade into the typical O. rivulare. We do not perceive such intergradation, and provide additional characters of differentiation. With this revision of the Vitt (1973) circumscription of Orthotrichum rivulare the Section Rivularia Schimp. includes three species instead of the two cited by Lewinsky (1993). Doubt has, however, been expressed if this section should be retained at all. Pierrot (1978) challenged its value stating: La sous-section Rivularia (Schp.) Broth. isolant les hygrophiles O. rivulare & O. sprucei B des caractbres fallacieux; si l'on considbre les dimensions des cellules (comme on l'a fait pour rattacher O. pumilum & la section Diaphana) il faudrait cr6er une s/sect. 0007-2745/98/295-302$0.95/0 This content downloaded from 207.46.13.102 on Sat, 30 Jul 2016 04:39:00 UTC All use subject to http://about.jstor.org/terms 296 THE BRYOLOGIST [VOL. 101 sp6ciale pour O. sprucei (cellules trbs grandes: 20 mu); I'&cologie, la forme des feuilles sont ici 6videmment particulibres, mais cela ne justifie peut&tre pas une sous-section. Further, a recent cladistic analysis of the relationships within the genus Orthotrichum provided no support for a separate group for these three species (Lewinsky-Haapasaari & Hedentis ms.). Because of past confusion, it seems appropriate now to provide revised descriptions of the three species.