Summary: Angiosperms, which inhabit diverse environments across all continents, exhibit significant variation in genome sizes, making them an excellent model system for examining hypotheses about the global distribution of genome size. These include the previously proposed large genome constraint, mutational hazard, polyploidy‐mediated, and climate‐mediated hypotheses. We compiled the largest genome size dataset to date, encompassing 16 017 (> 5% of known) angiosperm species, and analyzed genome size distribution using a comprehensive geographic distribution dataset for all angiosperms. We observed that angiosperms with large range sizes generally had small genomes, supporting the large genome constraint hypothesis. Climate was shown to exert a strong influence on genome size distribution along the global latitudinal gradient, while the frequency of polyploidy and the type of growth form had negligible effects. In contrast to the unimodal patterns along the global latitudinal gradient shown by plant size traits and polyploid proportions, the increase in angiosperm genome size from the equator to 40–50°N/S is probably mediated by different (mostly climatic) mechanisms than the decrease in genome sizes observed from 40 to 50°N northward. Our analysis suggests that the global distribution of genome sizes in angiosperms is mainly shaped by climatically mediated purifying selection, genetic drift, relaxed selection, and environmental filtering.

Transposable elements (TEs) are considered to be an important source of genome size variation and genetic and phenotypic plasticity in eukaryotes. Most of our knowledge about TEs comes from large genomic projects and studies focused on model organisms. However, TE dynamics among related taxa from natural populations and the role of TEs at the species or supra-species level, where genome size and karyotype evolution are modulated in concert with polyploidy and chromosomal rearrangements, remain poorly understood. We focused on the holokinetic genus Eleocharis (Cyperaceae), which displays large variation in genome size and the occurrence of polyploidy and agmatoploidy/symploidy. We analyzed and quantified the long terminal repeat (LTR) retrotransposons Ty1-copia and Ty3-gypsy in relation to changes in both genome size and karyotype in Eleocharis. We also examined how this relationship is reflected in the phylogeny of Eleocharis.

The dispersed occurrence of holocentric chromosomes across eukaryotes implies they are adaptive, but the conditions under which they confer an advantage over monocentric chromosomes remain unclear. Due to their extended kinetochore and the attachment of spindle microtubules along their entire length, holocentric chromosomes tolerate fragmentation; hence, they may be advantageous in times of exposure to factors that cause chromosomal fragmentation (clastogens). It is shown that holocentric organisms may, indeed, thrive better than monocentric organisms under clastogenic conditions and that such conditions of various duration and intensity have occurred many times throughout the history of Earth’s biota. One of the most important clastogenic events in eukaryotic history, in which holocentric chromosomes may have played the key role, was the colonization of land by plants and animals half a billion years ago. In addition to arguments supporting the anticlastogenic hypothesis of holocentric chromosomes and a discussion of its evolutionary consequences, experiments and analyses are proposed to explore this hypothesis in more depth. It is argued that the tolerance to clastogens explains the origin of holocentric lineages and may also have far-reaching consequences for eukaryotic evolution in general as exemplified by the potential role of holocentric chromosomes in terrestrialization.