A Naturally Occurring Moss Hybrid between Orthotrichum gymnostomum and O. obtusifolium from Newfoundland, Canada

Abstract

Orthotrichum gymnostomum Brid. gametophytes were found with sporophytes hav- ing characters intermediate between that species and the closely related 0. obtusifolium. The most important character of these anomalous sporophytes is a single peristome, as opposed to the double peristome of O. obtusifolium and the eperistomate condition of O. gymnostomum. 0. gymnosto- mum and 0. obtusifolium were growing intermixed, and the intermediate sporophytes are inter- preted as naturally occurring hybrids between the two species. The spores in the hybrid capsules are wrinkled and appear to have been aborted. Hybridization between the two species is briefly discussed in relation to their ecology and North American range. Section Orthophyllum of the genus Orthotrichum includes two species, 0. gymnostomum Brid. and 0. obtusifolium Brid. (Vitt 1973). Because of their dioicous inflorescences and round leaf tips, char- acters unique in the genus, the two species have been considered by some authors to constitute a separate genus, Stroemia Hag., or Nyholmiella Holmen & Warnke. Orthotrichum obtusifolium and 0. gymnosto- mum may be distinguished from each other on the basis of the peristome, which is double in the former and lacking in the latter. Gametophytes of the two species are easily separated by leaf margins and cell papillosity: 0. gymnostomum has inrolled margins and two papillae per leaf cell surface while O. ob- tusifolium has erect margins and unipapillose cell surfaces. In the course of recent field work in Terra Nova National Park, Newfoundland, I collected (from two sites a few kilometres apart) two fruiting specimens (Hedderson 2279, 2336 (NFLD)) of an epiphytic Or- thotrichum with gametophytes identical to those of Orthotrichum gymnostomum, including the critical state of each cell having two papillae on each surface (Vitt 1973). The sporophytes, however, had peri- stomate rather than gymnostomous capsules, and several characters that were intermediate between 0. gymnostomum and 0. obtusifolium. These anomalous sporophytes, described below, are compared to typical sporophytes of 0. gym- nostomum and 0. obtusifolium in Table 1. Infor- mation on the last two is taken from descriptions in the literature (Vitt 1973; Smith 1978; Crum & Anderson 1981; Ireland 1982), supplemented by examination of approximately 30 sporophytes of each species. Information on the intermediate spec- imens is based on examination of 9 sporophytes. All specimens examined are located at NFLD. Description of the intermediate sporophytes. Se- tae 0.3-0.4 mm long; urn of capsule emergent to ? exserted, 1.5-2.0 mm long including the neck (0.50- 0.75 times as long as the urn), obovate, not con- stricted below the mouth when dry, strongly 8-pli- cate, pale brown to yellow-brown; exothecial cells TABLE 1. A comparison of characters of the intermediate sporophytes with those of Orthotrichum gymnostomum and 0. obtusifolium.