At the beginning of the twentieth century, Plagiothecium nemorale s.l. and P. succulentum, both belonging to P. sect. Orthophyllum, were considered to be distributed across almost the entire Northern Hemisphere. However, in the mid-twentieth century these taxa were recircumscribed resulting in their exclusion from the North American bryoflora and restricting their distributions to Asia and Europe, and in the case of Plagiothecium nemorale s.l., also North Africa. More recently, it was found that P. nemorale s.l. is a taxonomic complex comprising three distinct species: P. nemorale s.s., P. longisetum, and P. angusticellum. I revised the North American material of P. section Orthophyllum deposited in three herbaria (NY, FH, F) and found that five examined taxa of the section are present in the North America. Two of the species P. angusticellum and P. longisetum, have not been recorded from North America previously, while two others, P. nemorale and P. succulentum, had not been listed in the North American bryoflora for 50 years. One taxon is new for the U.S.A. – P. succulentum f. propaguliferum. Here I provide detailed descriptions of the anatomical and morphological features of the recorded taxa along with photographic documentation of their most important characteristics. I also summarize their known distributions in North America and ecological preferences and provide a key for their identification.

中文翻译：

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重新评估北美苔藓植物中斜壳菌属的分类多样性

二十世纪初，Plagiothecium nemorale sl 和P. succulentum，均属于P. sect。Orthophyllum，被认为分布在几乎整个北半球。然而，在 20 世纪中叶，这些分类群被重新限制，导致它们被排除在北美苔藓植物群之外，并将它们的分布限制在亚洲和欧洲，在 Plagiothecium nemorale sl 的情况下，也是北非。最近，发现 P. nemorale sl 是一种分类学复合体，包括三个不同的物种：P. nemorale ss、P. longisetum 和 P. angusticellum。我修改了存放在三个植物标本馆（NY、FH、F）中的 P. section Orthophyllum 的北美材料，发现该部分的五个检查类群存在于北美。两种 P. angusticellum 和 P. longisetum 之前没有在北美被记录，而另外两种 P. nemorale 和 P. succulentum 已经有 50 年没有被列入北美苔藓植物群了。一个分类群对美国来说是新的——P. succulentum f。繁殖体。在这里，我详细描述了记录的分类群的解剖学和形态学特征，以及它们最重要特征的照片记录。我还总结了它们在北美的已知分布和生态偏好，并提供了识别它们的关键。在这里，我详细描述了记录的分类群的解剖学和形态学特征，以及它们最重要特征的照片记录。我还总结了它们在北美的已知分布和生态偏好，并提供了识别它们的关键。在这里，我详细描述了记录的分类群的解剖学和形态学特征，以及它们最重要特征的照片记录。我还总结了它们在北美的已知分布和生态偏好，并提供了识别它们的关键。