Revisiting the Dimerostemma collection in Rio Grande do Sul, the southernmost state of Brazil, one new species of Dimerostemma is described and another is resurrected. Although previously synonymized under Dimerostemma arnottii , Dimerostemma oppositifolium is here resurrected based on its distinct opposite leaves, linear to lanceolate leaf limbs, and specific pappus scale measurements. Additionally, Dimerostemma ramboi is described as a new species endemic to the state of Rio Grande do Sul. It resembles D. arnottii but is distinguished by its opposite leaves (sometimes whorled at the apex), subcordate to rounded leaf bases, and shorter floral structures, such as the ray floret tube and pappus aristae. We provide morphological descriptions, photo plates, its distribution is mapped, and preliminary conservation status for both taxa. Furthermore, an identification key and an occurrence map for the seven species of Dimerostemma now recognized for Rio Grande do Sul are presented.
Geological and climatic changes associated with the Ailao Shan–Red River shear zone (ARSZ) are thought to have influenced the evolutionary history of many mostly drought‐adapted low‐elevation plant lineages in southwestern China, yet their role in shaping genetic divergence in montane cloud‐forest plants remains poorly understood. Sladenia (Sladeniaceae), a rare tree genus comprising two species distributed across the ARSZ, provides an opportunity to examine the evolutionary consequences of these historical processes. Here, we integrated expanded plastome sampling with newly assembled nuclear ribosomal ITS sequences to reconstruct phylogenetic relationships within the genus. Plastome data recovered an northeast–southwest geographic structure among populations of S. celastrifolia across the Red River, with S. integrifolia being sister to the northeastern lineage. In contrast, the nuclear ITS data supported both species as monophyletic and resolved them as sister lineages, supporting the recognition of S. integrifolia as a distinct species and revealing marked cytonuclear discordance. Ecological niche modeling indicated the contraction of suitable habitat into southern refugia during the Last Glacial Maximum, followed by postglacial expansion. Together, these findings suggest that montane cloud‐forest plants share the east–west phylogeographic structure documented in lowland lineages, while retaining distinct signatures of both tectonic history and Quaternary climatic change. By integrating plastid and nuclear evidence, our study provides new insights into lineage divergence across the ARSZ.
Bupleurum oslaense sp. nov., a new member of the family Apiaceae, is described and illustrated based on the collections from Uttarakhand, India. The species shows close affinity to the Chinese element Bupleurum petiolulatum , but can be readily distinguished by its stout habit, higher number of rays, markedly larger bracts, and greater number of flowers per umbellule. Its systematic position has been evaluated using the nuclear ribosomal internal transcribed spacer (ITS) region through the phylogenetic tree reconstruction using maximum likelihood (ML) and Bayesian inference (BI) analysis, which supports its recognition as a distinct species. The conservation status has been assessed following standard IUCN guidelines.
In Arctic tundra, the majority of plant biomass is belowground. As temperatures increase and permafrost thaws, new soil volume containing nitrogen becomes available for plant roots, potentially leading to new plant–soil interactions. Whether or not different plant communities adapt their rooting depth distribution in response to increasing active layer thickness, whether roots at depth are similar to shallow ones, and if deep‐rooting species potentially redistribute thawed‐out nitrogen into more shallow layers remains poorly understood. We studied root biomass, rooting‐depth distribution, root dry matter content (RDMC), and 15 N natural abundances in a low Arctic peatland. We did this in two plant communities, dominated either by the graminoid Eriophorum vaginatum or by various dwarf shrubs, each with either a shallow (51.3 ± 0.9 cm) or a deep (69.4 ± 1.9 cm) active layer. Root biomass declined sharply with depth but did not differ between plant communities or active layer thicknesses, although roots reached the thawfront. RDMC was unaffected by active layer thickness, but was lower in E. vaginatum and declined with depth for roots of both functional types. This suggests relatively more acquisitive roots with faster growth and shorter lifespan in deeper soils. Presence of the deep‐rooting E. vaginatum increased foliar δ 15 N ratios of other species, indicating a potential redistribution of nitrogen in the soil column. Our results suggest that, despite the presence of deep‐rooting plants and roots down to the thawfront in shallow and deep active layers, rooting depth distribution remains relatively constant. This indicates that an increase in deep roots in response to thawing permafrost is relatively species‐specific and might not result in measurable differences in root biomass or its distribution, irrespective of plant community. The decreasing RDMC with depth illustrates that resource strategies vary not only among species but also with soil depth, with implications for carbon and nutrient cycling.
