Current morphometric methods that comprehensively measure shape cannot compare the disparate leaf shapes found in seed plants and are sensitive to processing artifacts. We explore the use of persistent homology, a topological method applied as a filtration across simplicial complexes (or more simply, a method to measure topological features of spaces across different spatial resolutions), to overcome these limitations. The described method isolates subsets of shape features and measures the spatial relationship of neighboring pixel densities in a shape. We apply the method to the analysis of 182,707 leaves, both published and unpublished, representing 141 plant families collected from 75 sites throughout the world. By measuring leaves from throughout the seed plants using persistent homology, a defined morphospace comparing all leaves is demarcated. Clear differences in shape between major phylogenetic groups are detected and estimates of leaf shape diversity within plant families are made. The approach predicts plant family above chance. The application of a persistent homology method, using topological features, to measure leaf shape allows for a unified morphometric framework to measure plant form, including shapes, textures, patterns, and branching architectures.

45Current morphometric methods that comprehensively measure shape cannot compare the 46 disparate leaf shapes found in seed plants and are sensitive to processing artifacts. We explore 47 the use of persistent homology, a topological method applied across the scales of a function, to 48 overcome these limitations. The described method isolates subsets of shape features and 49 measures the spatial relationship of neighboring pixel densities in a shape. We apply the 50 method to the analysis of 182,707 leaves, both published and unpublished, representing 141 51 plant families collected from 75 sites throughout the world. By measuring leaves from 52 throughout the seed plants using persistent homology, a defined morphospace comparing all 53 leaves is demarcated. Clear differences in shape between major phylogenetic groups are 54 detected and estimates of leaf shape diversity within plant families are made. This approach 55 does not only predict plant family, but also the collection site, confirming phylogenetically 56 invariant morphological features that characterize leaves from specific locations. The 57 application of a persistent homology method to measure leaf shape allows for a unified 58 morphometric framework to measure plant form, including shape and branching architectures. 59 60 Introduction 61 62As generally flattened structures, leaves provide a unique opportunity to quantify morphology 63 as a two-dimensional shape. Local features (such as serrations and lobes) and general shape 64 attributes (like length-to-width ratio) can be measured, but numerous methods also exist to 65 measure leaf shape more globally and comprehensively. A popular method to quantify leaf 66 shape is to place ( , ) coordinates, known as landmarks, on homologous features that are 67 related by descent from a common ancestor on every sample (Bookstein, 1997). The set of 68 landmarks from each leaf can be superimposed by translation, rotation, and scaling using a 69Generalized Procrustes Analysis (Gower, 1975). Once superimposed, the Procrustes-adjusted 70 coordinates of each shape can be used directly for statistical analyses. Landmark analysis excels 71

PREMISE A disjunct distribution, where a species’ geographic range is discontinuous, can occur through vicariance or long‐distance dispersal. Approximately 75 North American plant species exhibit a ~650 km disjunction between the Ozark and Appalachian regions. This disjunction is attributed to biogeographic forces including: (1) Eocene–Oligocene vicariance by the formation of the Mississippi embayment; (2) Pleistocene vicariance from interglacial flooding; (3) post‐Pleistocene northward colonization from separate glacial refugia; (4) Hypsithermal vicariance due to climate fluctuations; and (5) recent long‐distance dispersal. We investigated which of these pathways most likely gave rise to the Appalachian‐Ozark disjunction in Delphinium exaltatum. METHODS We genotyped populations of D. exaltatum from five Ozark and seven Appalachian localities, analyzed genetic structure, tested the order and timing of divergences using DIYABC, and conducted niche reconstructions up to 21,000 years before present (YBP). RESULTS Populations fell into five main genetic clusters, i.e., a group in the central Appalachians, and four “lowland” groups. DIYABC analyses showed the central Appalachian and lowland lineages diverging 11,300 to17,000 YBP, and the lowland groups diverging 6800 to 10,900 YBP. Niche reconstructions showed that suitable climate for the central Appalachian lineage experienced large spatial discontinuity starting 14,000 YBP, such that divergence and persistence before this period is less plausible than divergence thereafter. CONCLUSIONS Our results did not fully support any of the original hypotheses. Rather, the oldest divergence likely occurred after 13,500 YBP through expansion into newly opened habitat in the Appalachians. The Appalachian‐Ozark disjunction likely resulted from northward dispersal of the lowland lineage as climate warmed during the Holocene.

Chromosome number change is a driver of speciation in eukaryotic organisms. Carnivorous sundews, the plant genus Drosera L., exhibit single chromosome number variation among and within species, especially in the Australian Drosera subg. Ergaleium D.C., potentially linked to the presence of holocentromeres. We reviewed literature, verified chromosome counts, and using an rbcL chronogram, tested alternate models where the gain, loss, and doubling rates (+1, −1, ×2) were the same or different between D. subg. Ergaleium and the other subgenera. Ancestral chromosome number estimations were performed, and the distributions of self-compatibility and genome size were visualized across the genus. The best model for chromosome evolution had equal rates of polyploidy (0.014 per million years; Myr) but higher rates of single chromosome number gain (0.19 and 0.027 per Myr) and loss (0.23 and 0.00059 per Myr) in D. subg. Ergaleium compared to the other subgenera. We found no evidence for differences in single chromosome evolution to be due to differences in diploidization after polyploidy or to holocentromeres as had been proposed. This study highlights the complexity of factors influencing rates of chromosome number evolution.