A plant embryo development stage (PO:0007631) that occurs during the interval between the transition from radial to bilateral symmetry in a plant embryo proper (PO:0000001) and the onset of either the plant embryo cotyledonary stage (PO:0001078) or the plant embryo coleoptilar stage (PO:0001094). [source: PMID:24784759, POC:Laurel_Cooper, POC:Ramona_Walls, TAIR:Katica_Ilic]
Comment
A plant embryo bilateral stage is commonly known as the heart stage in dicotyledonous plants and the transition stage in monocots. Preceded by a plant embryo globular stage (PO:0001185).