Rhynchospora tenuis

Meiotic recombination ensures accurate chromosome segregation and promotes genetic diversity by generating crossovers (COs) between homologous chromosomes. While essential in most sexually reproducing organisms, recombination is variably regulated and can be entirely absent in some lineages, a phenomenon known as achiasmy. However, obligate achiasmy in both sexes of a sexually reproducing species has not been previously documented. Here, we investigate the beak-sedge Rhynchospora tenuis, a holocentric plant with the lowest known chromosome number in angiosperms (n = 2) and inverted meiosis. Using chromosome-scale genome assemblies from nine accessions, immunocytochemistry, single-gamete sequencing of over 10k pollen nuclei, and whole-genome sequencing of selfed progeny, we show that R. tenuis undergoes obligate, genome-wide achiasmy in both male and female meiosis. Despite normal early meiotic axis formation, synapsis fails, COs are not detected cytologically or genetically, and univalents persist at metaphase I. Striking haplotype-specific structural variants and accumulation of transposable elements (TEs) are associated with strong segregation distortion, favouring the transmission of larger, TE-rich chromosomes. Biparental genomic contributions are retained, yet all progeny are genetically identical to the maternal plant, mimicking clonal reproduction. We propose that recombination loss, combined with holocentricity, inverted meiosis, and meiotic drive mediated by TE-associated fitness effects, enables faithful chromosome segregation and clonal-like inheritance despite sexual reproduction. This discovery challenges the classical dichotomy between sexual and asexual reproduction and reveals a novel evolutionary route linking genome architecture, recombination loss, and transmission bias.