As usual in dicotyledonous angiosperms, the seedlings of subfam. Sanangoideae and subfam. Gesnerioideae (Coronantheroid and Gesnerioid Gesneriaceae sensu Weber 2004) comprise two equal cotyledons (they are “isocotylous”, from the Greek isos = equal), a hypocotyl, and a radicle. Germination is “phanerocotylar”, with the two unfolding cotyledons being the first photosynthetic organs.
In subfam. Didymocarpoideae (Epithematoid and Didymocarpoid Gesneriaceae) a different pattern occurs (see illustrations below). The two cotyledons show unequal growth – they are “anisocotylous” (from the Greek anisos = unequal). One cotyledon, the “macrocotyledon”, shows continuous growth, while the other, the “microcotyledon”, remains small and is without function. The development of a shoot apical meristem is often delayed and displaced to the base of the macrocotyledon. In Monophyllaea, in the “unifoliate” species of Streptocarpus and in a few other genera, the larger cotyledon (macrocotyledon) develops into the only foliar organ of the plant and grows continuously during the whole lifetime of the plant (see Exceptional Morphologies).
