Ginkgoopsida

(botany) A class of the subdivision Pinicae containing the single, monotypic order Ginkgoales.

A class of largely extinct gymnosperms (Pinophyta). Included orders are Calamopityales, Callistophytales, Arberiales, Peltaspermales, Ginkgoales, Leptostrobales, Caytoniales, Pentoxylales, and Ephedrales. The most ancient taxa, Calamopityales and Callistophytales, lived during the Carboniferous; the Arberiales, from late Carboniferous into the Triassic; the Peltaspermales, from Permian through Jurassic; the Leptostrobales and Caytoniales, from Triassic into the Cretaceous; and Ginkgoales, predominantly, from Triassic into the Cretaceous periods, with one species, Ginkgo biloba, persisting to the present. Ephedrales is the only largely extant group, but has a pollen fossil record beginning in the Upper Triassic. See also Caytoniales; Ephedrales; Ginkgoales.

These taxa, divergent in many characteristics, are unified by the presence in all of platyspermic (bilaterally symmetrical) seeds lacking cupules. In the most primitive, and some other, taxa of ginkgoopsids, the seeds and microsporangia are thought to have been borne on pinnately (featherlike) branched fertile structures. During the evolution of more advanced taxa, the individual microsporangia aggregated, fused to form synangia, and shifted onto leaves, causing additional changes to the microsporophylls and phyllosperms (seed-bearing leaves). In particular, the phyllosperms became greatly modified, often into peltate structures (as in advanced Peltaspermales) and stemlike structures (as in Ginkgo). See also Pinophyta; Plant kingdom.