In this review, we explore the origin of the rudimentary embryo, its relationship to other kinds of plant embryos and its role in the diversification of angiosperms. Rudimentary embryos have a length:width ratio of ≤2.0, and they have organs, including cotyledon(s) and a primary root. A literature survey failed to reveal rudimentary embryos in the pre-angiosperms, suggesting that this kind of embryo is an angiosperm invention. Although proembryos of some gymnosperms and angiosperms have a length:width ratio of ≤2.0, they have not formed meristems or organs. Thus, rudimentary embryos are not proembryos. During the development of rudimentary embryos in monocots and dicots (all non-monocots), the growth pattern of the epicotyledonary cells differs, resulting in differences in the placement of the shoot meristem and in one versus two cotyledons, respectively, but the embryo size is similar. Rudimentary embryos grow inside the seed prior to germination, which is true for linear-underdeveloped embryos, including those in some gymnosperms. Rudimentary embryos served as the starting point for the great diversification of embryos, and ultimately of seeds, in angiosperms, and they are still present in many families of extant angiosperms. The rudimentary embryo is part of the syndrome of changes, including increased speed of pollen germination and pollen tube growth, simplification of the female gametophyte, development of endosperm and elimination of multiple embryo production from each zygote, that distinguish angiosperm seed production from that of gymnosperms. We conclude that the rudimentary embryo was one of many new developments of angiosperms that contributed to their great success on earth.

Twelve localities of Lower Carboniferous strata in Scotland (Loch Humphrey Burn, Glenarbuck, Pettycur, Oxroad Bay and the Berwickshire localities of Cove, Burnmouth, Gavinton, Edrom, Foulden) and in France (Esnost, Roannais, Montagne Noire) have been investigated with particular regard to their anatomically preserved floras. New data on the composition and preservation of the assemblages, their geological setting and stratigraphical age, using palynology in particular, are presented. Present data suggest that four successive groups of floras obtained from these localities can be recognised: from the Montagne Noire (mid to late Tournaisian), from the Berwickshire localities and Oxroad Bay (late Tournaisian to early Viséan), from Loch Humphrey Burn and possibly Glenarbuck (mid Viséan) and from Roannais, Esnost, and Pettycur (late Viséan). The similarities and differences between the floras are discussed with particular emphasis on stratigraphical as opposed to ecological controls. Comparisons are made with the New Albany Shale floras of the U.S.A., the Saalfeld and Glätzish-Falkenberg floras from the German Democratic Republic. The data suggest that the ferns and pteridosperms show the most striking changes through the Lower Carboniferous strata.