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Gesneriaceae: |
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As usual in dicotyledonous angiosperms, the seedlings of Coronantheroid and Gesnerioid Gesneriaceae 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 the 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. |
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