The diversity of the Polytrichopsida—a review

Abstract

The class Polytrichopsida are a phylogenetically isolated moss lineage of around 200 species. The nematodontous peristome found in most species has a fundamentally different structure from the arthrodontous peristome of the Bryopsida and may be independently evolved from an ancestral type of spore dehiscence apparatus. Within the class generic circumscriptions and relationships are now fairly confidently resolved and more or less congruent with the most developed pre-molecular taxonomy. Drawing on previously published datasets, we conducted a phylogenetic analysis of a novel matrix of terminals representing diversity across the Polytrichopsida. The class comprises 17 extant genera and two known only from fossils. Most of these are numerically small, the most notable exception being Pogonatum with over 50 species. Considering current phylogenetic hypotheses in the light of morphology and global distributions, Alophosia, Bartramiopsis and Lyellia, the earliest diverging lineages according to recent phylogenetic analyses, appear to be relicts, with scattered and disjunct distributions. All of these genera lack peristomes, while all later originating lineages have nematodontous peristomes developed from bundles of “u-shaped” whole cells. The genus Dawsonia, sister to all other peristomate taxa, differs in its unique peristome composed of long, bristle-like teeth arranged in concentric layers. Many members of some traditional genera found to be polyphyletic in recent studies are part of a southern hemisphere grade and only distantly related to the superficially similar northern hemisphere species with which they were historically classified. A large apical clade including eight genera accounts for the majority of the diversity, these being most speciose in northern temperate regions or the Asian tropics. Many of the Polytrichopsida are relatively large plants with well-developed vasculature and a “pseudo-mesophyll” capable of supporting relatively high rates of photosynthesis in moist, well-illuminated environments. With ten described species, Cenozoic fossils of Polytrichopsida are fairly numerous compared with other mosses. Records of fossils from older sediments have been rare, but recently several well-preserved fossils of Polytrichopsida have been found, most of which still await detailed description.

A New Record of Pogonatum tahitense (Polytrichaceae) from Tibet, China: Taxonomic Description, Range Expansion, and Biogeographic History

“…While all three species share a diminutive size and an Asian distribution, P. spinulosum possesses distinct features, such as a persistent protonema, leaves appressed on stems, and the absence of lamellae, rendering its phylogenetic position uncertain [ 4 ]. Notably, many Pogonatum species remained unresolved with low posterior probability in our Bayesian analysis, consistent with previous studies that exhibited similar topologies [ 2 , 6 , 7 ]. It is crucial to acknowledge that previous analyses primarily utilized DNA fragments for elucidating the phylogenetic relationships within Pogonatum [ 2 , 6 , 7 ].…”

“…Notably, many Pogonatum species remained unresolved with low posterior probability in our Bayesian analysis, consistent with previous studies that exhibited similar topologies [ 2 , 6 , 7 ]. It is crucial to acknowledge that previous analyses primarily utilized DNA fragments for elucidating the phylogenetic relationships within Pogonatum [ 2 , 6 , 7 ]. Thus, a comprehensive phylogenomic analysis of this genus is imperative to resolve its intricate phylogenetic relationships.…”

“…Specifically, Polytrichastrum sexangulare was consistently placed on a distinct branch, divergent from the primary Polytrichastrum clade, in both analytical approaches. Previous research had similarly found P. sexangulare to be poorly resolved with the Polytrichastrum clade [ 7 , 17 , 18 ], suggesting that P. sexangulare may represent one previously undescribed genus [ 2 ].…”

“…The family Polytrichaceae Schwägr. [ 1 ] encompasses approximately 200 species and comprises 17 extant genera [ 2 ]. Pogonatum P. Beauv.…”

“…Pogonatum P. Beauv. [ 3 ] stands out as the most diverse genus within the family, containing over 50 species characterized by distinct morphological features of sporophytes, including a lack of stomata, deeply pigmented peristome, and a mammillose exothecium [ 2 , 4 ]. Previous phylogenetic studies consistently posited Pogonatum as monophyletic, positioned as the sister genus to Polytrichum Hedw.…”