Ovule and pollen development in the natural hybrid Drosera x obovata Mert. & Koch (Droseraceae) and its parents

A light microscopy study about sporogenesis and gametogenesis of the natural hybrid Drosera x obovata and its parental species (D. rotundifolia and D. anglica) was carried out. Even though D. x obovata and its parents have been investigated cytologically in detail during the past century and a “Drosera scheme” for pairing of chromosomes has been described, there are no data about sporogenesis and gametogenesis of the European sundews. We report a morphological description of the ovule and pollen development in D. x obovata and its parents. D. x obovata, even if sterile, produces a male and a female gametophyte, structurally the same as that of its parents. However, its pollen grains have a reduced number of protoplasmic papillae, which indicates low vitality, whereas in the ovule it has never been possible to observe an embryo. Hybridization is considered as a mechanism for speciation in some Drosera as proved by the hybrid origins of several species.