Flora of North America species comparison

Grimmia ovalis is common and widespread in high elevation sites in western North America from southern British Columbia along the Rocky Mountain corridor to southern New Mexico and south central California. H. A. Crum and L. E. Anderson (1981) rejected all reports of G. ovalis from eastern North America. However, we have seen specimens from that area, although scattered and rare. It is not surprising that the species occurs in the eastern part of the continent given that it is widespread across the Laurasian continental plates and in India. Outlier sites in the Yukon and southern Greenland connect the North American populations to those in Asia and Europe, respectively. In western North America, G. ovalis is most often confused with G. longirostris and G. laevigata. While superficially similar to G. longirostris, G. ovalis has concave leaves with plane margins and is dioicous, while G. longirostris has keeled leaves with a recurved margin and is autoicous. Other points of separation are discussed under G. longirostris. Typical specimens of G. ovalis are readily separated from G. laevigata by their ovate-lanceolate leaves with a well-defined ovate base and narrowly attached awns. However, both of these species are variable in leaf shape, and while the awn of G. ovalis is usually narrowly attached, sometimes it is quite broad and may border on being decurrent. These specimens can be identified by the width of the costa and the basal areolation. Grimmia ovalis has a costa that is narrow at the base, while G. laevigata has a distinctly broad costa covering up to 1/3 of the base. The basal marginal cells of G. ovalis are most often short- to long-rectangular and hyaline while those of G. laevigata are always oblate to quadrate and not hyaline. In eastern North America, specimens of G. ovalis have been misidentified as G. olneyi. Aside from seta and capsule differences, G. ovalis has rectangular basal marginal laminal cells and its basal juxtacostal cells are long-rectangular to elongate; see also under G. olneyi.

Based on identifications by Greven, W. A. Weber et al. (2003) reported Grimmia bernoullii in the United States. That species differs from G. ovalis by its more ovate leaves without shoulders and with plane margins, costa broad at the base and disappearing in mid leaf, and sporophytically by its ellipsoid capsule with long-rostrate, straight operculum, and mitrate calyptra. Hastings has examined duplicate specimens from Missouri of those cited by Weber et al. and has determined that they do not deviate significantly from G. ovalis, having rather narrow leaves, costa narrow at the base and remaining strong in mid leaf, and with many leaves having incurved margins. The specimens were sterile and therefore sporophytic characters could not be determined. Based on these observations Hastings excludes G. bernoullii from the North American flora, although Greven would still retain the species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Grimmia caespiticia is an uncommon species that occurs on siliceous rock outcrops above timberline in western North America. J. Muñoz (1998b) reported the species on dry rock, but H. C. Greven (1995) cited it as being hygrophytic. Hastings has observed specimens most commonly in moist areas, but occasionally also on dry rock. Grimmia caespiticia does not occupy sites as extreme as those of G. sessitana, being found at somewhat lower latitude and elevations. Except for a single site in New York state, it is not known from east of the front ranges of Colorado. Grimmia caespiticia and G. elongata are the only members of the Montanae group (in the sense of Muñoz) to be both dioicous and have stomata. Grimmia caespiticia typically has a cucullate leaf apex, a feature unknown in other members of the Montanae group and very rare in Grimmia. For most North American specimens, the cucullate apex is more easily seen than are the leaf plications. While usually present, the plications are often not evident except in transverse section. Eurasian specimens typically have, however, strongly developed plications. Most specimens of G. caespiticia have been misidentified as G. alpestris. These two species are similar in habit, have ovate leaves with incurved margins, may have bulging laminal cells, and are dioicous. However, G. caespiticia has stomata while G. alpestris has none. If a specimen has a cucullate leaf apex and/or the plications are well-developed in transverse section then it is most certainly G. caespiticia.

Grimmia caespiticia may also be confused with G. sessitana. These species are both found above timberline and both have bulging laminal cells and capsules with stomata. However, the incurved leaf margins, cucullate apex, and quadrate to short-rectangular basal areolation of G. caespiticia are quite different from the plane to recurved leaf margins with long-rectangular basal areolation typical of G. sessitana. Although the type specimen of G. alpestris var. holzingeri lacks capsules, gametophytically it is indistinguishable from muticous specimens of G. caespiticia. Specimens of var. holzingeri with capsules have been collected near the type locality and these specimens have stomata. Rather than accepting that G. alpestris may have stomata (in the sense of E. Lawton 1971), Hastings places var. holzingeri within the concept of G. caespiticia. In 1890, Kindberg described G. nivalis based on a specimen collected by J. Macoun at a high elevation site in southern British Columbia. This taxon is similar to G. caespiticia, differing mainly by having papillae on the leaf lamina. Having examined the type and other material of G. nivalis, Hastings interprets these features to be merely the remnants of laminal cell walls; the exterior surface of the strongly bulging cell wall has been worn away by the elements. H. C. Greven (2003) believed that the somewhat longer awns and weak plications of G. nivalis fit well with European specimens of G. pyrenaica, a taxon that has also been put in synonymy with G. caespiticia. Therefore, we place G. nivalis in synonymy with G. caespiticia.

(Discussion copyrighted by Flora of North America; reprinted with permission.)