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A simplified maximum likelihood phylogeny of Selaginellaceae based on plastid rbcL and five nuclear markers. Sizes of black triangles are proportional to sample sizes of individual clades. Support values (maximum likelihood bootstrap support, maximum parsimony jackknife support, and posterior probability) are shown on the branches. „*” indicates 100% support value. The red and green names represent the 7 subfamilies and 19 genera, respectively, recognized in the current classification. Blue and black Latin names represent subspecies and sections recognized by Zhou and Zhang (2015). Black Chinese names refer to Chinese vernacular names of the breed. Purple names represent the 6 categories recognized by Zhou and Zhang (2015) and this study. Credit: Xin-Mao Zhou, Yunnan University, China, Li-Bing Zhang, Missouri Botanical Garden
Clubmoss (Selaginella sensu lato) predated the dinosaurs in the Devonian period, 383 million years ago. These ancient vascular plants are of significant value in unraveling land plant evolution. Currently, Selaginella is the sole member of the family Selaginellae and the order Selaginellas.
Notably, this order/family has significant diversity within pteridophytes (ferns and lycophytes), comprising 750 or more species. The acceptance of Selaginella as broadly defined is attributed to two main factors. First, the current type species of the genus, S. selaginoides, stands within a two-species subgroup lacking rhizophores, a complete departure from all other genus members.
Acceptance of different genera would require renaming all but these two non-rhizophorous species. Second, the adoption of a broadly defined Selaginella is rooted in the complexity of phylogenetic relationships within the genus. Despite previous phylogenetic studies, uncertainty remains, and morphological homoplasy has not been adequately assessed within an appropriate phylogenetic framework.
In a recent study, an American and a Chinese researcher used DNA sequences from 1 nuclear and 5 chloroplast genomes in 684 global clubmoss samples. It includes approximately 300 species (40% of the total). The aim was to elucidate family relationships and, in particular, to pioneer the study of evolutionary patterns of 10 morphological traits.
The researchers discovered that clubmoses are consistently grouped into seven primary clades, four of which are further divided into 3, 3, 4 and 6 subclades. By combining molecular evidence with morphological attributes, spore characteristics and distribution data, the study led to the classification of clubmoses into 7 subfamilies and 19 genera, including 12 newly described species.
An alternative approach is to consider these 19 genera as subdivisions or sections within Selaginella, although this is often neglected by experienced plant taxonomists. Also, relying on species names that include genus can be very useful in highlighting distant (individual genus names) or close (shared genus names) relationships.
Furthermore, the separation of Selaginella sl into distinct and manageable species offers many advantages for analytical, communication and conservation purposes. This novel taxonomy encourages further research into this important lineage of land plants.
The article has been published in the journal Plant diversity.
More information:
Xin-Mao Zhou et al, Phylogeny, character evolution, and classification of Selaginellaceae (lycophytes), Plant diversity (2023) DOI: 10.1016/j.pld.2023.07.003
Presented by KeAi Communications.
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