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Accurate species delimitation is the key to precise estimation of species diversity and is fundamental to most branches of biology. Unclear species boundaries within species complexes could lead to the underestimation of species diversity. However, species delimitation of species complexes remains challenging due to the continuum of phenotypic variations. To robustly examine species boundaries within a species complex, integrative approaches in phylogeny, ecology, and morphology were applied to the Stewartia sinensis complex (Theaceae) endemic to China. Multispecies coalescent‐based species delimitation using 572 nuclear ortholog sequences (anchored enrichment) supported reciprocal phylogenetic monophyly of the northern lineage (NL) and southern lineage (SL), which were not sister clades. Niche equivalency and similarity tests demonstrated significant climatic niche differentiation between NL and SL with observed Warren et al.'s I = 0.0073 and Schoener's D = 0.0021. Species distribution modeling also separated their potential distribution. Morphometric analyses suggested significant interlineage differentiation of multiple traits including the ratio of length and width, leaf width, and pedicel length, although overall similarity did not differ. Based on the integrative species concept, two distinct species were proposed with legitimate names of Stewartia gemmata for SL and S. sinensis for NL. Our empirical study of the S. sinensis complex highlights the importance of applying multiple species criteria, in particular the underappreciated niche differentiation, to species delimitation in species complexes pervasive in plants. [ABSTRACT FROM AUTHOR]

• Sand physico-chemical properties exhibited distinct changes across the intertidal zones on island beaches. • Consistent patterns of variation were observed in macrofaunal diversity and functional groups across the intertidal zones. • Variations in macrofaunal communities on island beaches were primarily influenced by sand moisture, salinity, and nutrition. • Island beaches are not ecological deserts, they require careful protection. Island beaches, once mistakenly considered as 'ecological deserts', are actually unique ecosystems that support abundant macrofaunal communities. However, limited studies have examined the variations and determinants of macrofaunal communities across the intertidal zones on island beaches, which is crucial for shedding light on the underlying ecological processes and enhancing biodiversity conservation efforts. Here, we explored the variations in macrofaunal communities along sand physico-chemical gradient across four intertidal zones on nine representative beaches, within the largest land-bridge archipelago in eastern China. Our findings revealed that species richness, density, and Shannon-Wiener diversity of macrofaunal communities were notably higher in the lower intertidal zones, exhibiting a positive correlation with elevated levels of sand moisture (M), electrical conductivity (EC), available potassium (AK), and grain size (GS). Conversely, macrofaunal Simpson diversity displayed an inverse pattern, with heightened values observed in the vegetation zone. The Saprophagous, Predaceous, and Omnivorous groups of macrofaunal communities demonstrated an increase with higher levels of EC, AK, and M in the lower intertidal zones. Furthermore, Phytophagous group of macrofaunal communities tended to inhabit the vegetation zones characterized by elevated levels of sand total phosphorus (TP), total nitrogen (TN), and organic carbon (OC). Primarily, our findings indicate that sand nutrition, moisture, and salinity play pivotal roles in shaping the variations of macrofaunal communities on island beaches. These insights offer valuable perspectives into the holistic responses of macrofauna on island beaches to changes in sand physico-chemical properties, serving as a crucial theoretical foundation for the assessment, conservation, and restoration of island beaches. [ABSTRACT FROM AUTHOR]

• Cyto-nuclear conflicts occurred in Stewartia s. l. phylogeny. • Hartia was nested in Stewartia s.s. with the basal S. malacodendron in America. • Introgression was prevailing in shallow phylogeny with a consistent backbone. • Ancient co-distribution and dispersal contributed to introgression in Asian. Phylogenetic analyses using diverse datasets can yield conflicting inference of evolutionary history. Phylogenetic conflicts observed in both animal and plant systems have often been explained by two competing (but not mutually exclusive) hypotheses, i.e., hybridization vs. incomplete lineage sorting (ILS). The likelihood of either process contributing to phylogenetic conflict in a given group is context-dependent, involving attributes of life history, distribution, and phylogeny, among others. Here we explore phylogenetic conflict in Stewartia s.l. , a genus with ca. 20 species of trees and shrubs from the tea family (Theaceae) disjunctly distributed between eastern Asia (EAS) and eastern North America (ENA). We use both restriction-site associated DNA sequencing (RAD-seq) and complete plastome sequence data to reconstruct the phylogeny of the group using concatenation and coalescence approaches. Our results indicate strong conflicts between the topologies reconstructed using nuclear and plastid data. Four-taxon D -statistic (ABBA-BABA) tests detected prevailing signals of introgression. Bayesian Analysis of Macro-evolutionary Mixtures (BAMM) inferred that species diversification occurred in the middle to late Miocene. Ancestral range reconstructions indicated co-distribution of ancestral species (represented by internal nodes) for both the Hartia clade (in southern China) and the EAS Stewartia s.s. clade (Japan Archipelago and the Yangtze Valley of China). The latter clade experienced multiple events of dispersal and vicariance during its diversification history. Ancient introgressive hybridization following species diversification in the mid- to late-Miocene likely caused diverging histories in the nuclear and plastid genomes, leading to phylogenetic conflict in Stewartia s.l. Our study indicates that species diversification driven by both the intensification of the East Asian summer monsoon since the late Miocene and reduced risks of extinction due to frequent dispersal possibly via East China Sea Land Bridge impacted the anomalous species richness between EAS and ENA. Our study highlights the importance of using data from different genomes while reconstructing deep and shallow phylogenies of organisms. [ABSTRACT FROM AUTHOR]