The megaspore membranes of Middle Jurassic Ginkgo yimaensis and Yimaia recurva are generally similar to each other in stratification. In this respect, they resemble also the megaspore membrane in mature ovules of Ginkgo biloba, but clearly differ from that of Cycas revoluta. The configuration of bacula in the patterned layer of mature ovules of both fossil and living ginkgos is essentially the same, while that of Yimaia recurva is slightly different. In Cycas revoluta, the patterned layer is quite differently constructed. Four developmental stages of the megaspore membranes of mature ovules of G. biloba are revealed by the present study. Considerable changes take place in the patterned layer, i.e. in the zonation and in the configuration of bacula, which appear to be mainly influenced by the diploid nucellus tissue rather than the haploid megaspore proper. The megaspore membrane in mature ovules of G. biloba appears to have developed structurally beyond that of G. yimaensis and may possibly be of peramorphosis origin.