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.

在这篇综述中，我们探讨了初级胚胎的起源、它与其他种类植物胚胎的关系及其在被子植物多样化中的作用。未发育胚的长宽比≤2.0，并且具有包括子叶和初生根在内的器官。文献调查未能揭示前被子植物中的初级胚胎，这表明这种胚胎是被子植物的发明。一些裸子植物和被子植物的原胚虽然长宽比≤2.0，但尚未形成分生组织或器官。因此，未发育的胚胎不是原胚胎。在单子叶植物和双子叶植物（所有非单子叶植物）的初级胚胎发育过程中，上子叶细胞的生长模式不同，导致芽分生组织的位置和其中一个相对分别有两个子叶，但胚胎大小相似。未发育胚胎在发芽前在种子内部生长，这对于线性发育不全的胚胎来说是正确的，包括一些裸子植物中的胚胎。初级胚胎是被子植物中胚胎以及最终种子多样化的起点，并且它们仍然存在于现存被子植物的许多科中。未发育胚是变化综合症的一部分，包括花粉萌发和花粉管生长速度加快、雌配子体简化、胚乳发育以及每个受精卵消除多个胚胎，这些都是被子植物种子生产与裸子植物区别的因素。