First discovery of an intersubgeneric hybrid Sparganium emersum × S. microcarpum (Typhaceae) based on morphological and molecular data

Hybridization is widespread in the genus Sparganium, but previously confirmed cases were restricted to crosses between species within the two subgenera (subg. Xanthosparganium or subg. Sparganium). Intersubgeneric hybridization had long been dismissed by most authoritative researchers, as experimental attempts to cross these lineages consistently failed. Here we reported Sparganium × papczenkovii Belyakov et Lapirov, a newly discovered natural hybrid resulting from the spontaneous hybridization between species of two Sparganium subgenera: S. emersum (subg. Xanthosparganium) and S. microcarpum (subg. Sparganium). The hybrid status of the found population was confirmed through principal coordinates analysis of seven morphological traits including tepal morphometrics comparing the hybrid, its putative parental species (S. emersum and S. microcarpum), and one more possible candidate – S. erectum. Sequence analysis of chloroplast and nuclear DNA further supported the hybrid origin, revealing that all examined S. × papczenkovii samples were heterozygous with S. emersum as the maternal parent and S. microcarpum as the paternal parent. We also found that all samples of S. × papczenkovii were F1 generations. We propose that post-zygotic reproductive isolation specifically, F1 sterility may maintain species boundary between S. emersum and S. microcarpum. Despite potential sterility, F1 hybrids in Sparganium exhibit significant ecological and evolutionary relevance, as their vegetative reproduction often grants them higher competitiveness compared to parental species.