Bibliography Details:
Author(s):
Tsou, Chih-Hua
Mori, S. A.
Tsou, Chih-Hua
Mori, S. A.
Article or Chapter Title:
Floral organogenesis and floral evolution of the Lecythidoideae (Lecythidaceae)
Floral organogenesis and floral evolution of the Lecythidoideae (Lecythidaceae)
Year:
2007
2007
Journal or Book:
American Journal of Botany; official publication of the Botanical Society of America 94(5): 716-736
American Journal of Botany; official publication of the Botanical Society of America 94(5): 716-736
Notes:
The subfamily Lecythidoideae of Lecythidaceae (Brazil nut family) is a dominant group in Neotropical forests, especially those of Amazonia. New World members of the family have large showy flowers that are either polysymmetric or monosymmetric. In this study, floral organogenesis of all ten Neotropical genera is examined using the SEM. Our observations of floral development are put into the context of a molecular phylogeny based on sequences of the ndhF and trnL-F genes (Amer. J. Bot. 94: 289-301). Floral evolution of the subfamily is explained as having undergone four different levels of complexity in regard to floral symmetry. The basal most genera, Grias and Gustavia, have polysymmetric flowers. At level two, represented only by species of Couroupita, monosymmetry is established through the expression of abaxial dominance that leads to the development of an androecial hood; at this level abaxial dominance impacts the perianth and androecium, but not gynoecium. At the third level, monosymmetry is developed in Couratari and Cariniana domestica; but, in the Allantoma/Cariniana lineage, a reversal back to polysymmetric flowers as the result of a gradual weakening of abaxial dominance and the loss of the hood has occurred. Finally, in level four, including Bertholletia, Corythophora, Eschweilera, and Lecythis, monosymmetry is so strongly expressed that the gynoecium is also influenced by abaxial dominance. In this group, the hood is complicated in both structure and function, and the floral axis is changed from straight to slightly inclined. Within the Lecythidoideae, the expression of abaxial dominance is associated with hexamery of the perianth parts. This study demonstrates that the establishment and development of abaxial floral dominance is the proximate cause of monosymmetry in the Lecythidoideae. We suggest that monosymmetric flowers are more efficiently pollinated and therefore the bees and bats that pollinate the monosymmetric flowers in this group are ultimately responsible for the monosymmetry.
KEYWORDS = flora evolution, floral organogenesis, floral symmetry, Lecythidaceae, Lecythidoideae, monosymmetry, pollination, polysymmetry.
The subfamily Lecythidoideae of Lecythidaceae (Brazil nut family) is a dominant group in Neotropical forests, especially those of Amazonia. New World members of the family have large showy flowers that are either polysymmetric or monosymmetric. In this study, floral organogenesis of all ten Neotropical genera is examined using the SEM. Our observations of floral development are put into the context of a molecular phylogeny based on sequences of the ndhF and trnL-F genes (Amer. J. Bot. 94: 289-301). Floral evolution of the subfamily is explained as having undergone four different levels of complexity in regard to floral symmetry. The basal most genera, Grias and Gustavia, have polysymmetric flowers. At level two, represented only by species of Couroupita, monosymmetry is established through the expression of abaxial dominance that leads to the development of an androecial hood; at this level abaxial dominance impacts the perianth and androecium, but not gynoecium. At the third level, monosymmetry is developed in Couratari and Cariniana domestica; but, in the Allantoma/Cariniana lineage, a reversal back to polysymmetric flowers as the result of a gradual weakening of abaxial dominance and the loss of the hood has occurred. Finally, in level four, including Bertholletia, Corythophora, Eschweilera, and Lecythis, monosymmetry is so strongly expressed that the gynoecium is also influenced by abaxial dominance. In this group, the hood is complicated in both structure and function, and the floral axis is changed from straight to slightly inclined. Within the Lecythidoideae, the expression of abaxial dominance is associated with hexamery of the perianth parts. This study demonstrates that the establishment and development of abaxial floral dominance is the proximate cause of monosymmetry in the Lecythidoideae. We suggest that monosymmetric flowers are more efficiently pollinated and therefore the bees and bats that pollinate the monosymmetric flowers in this group are ultimately responsible for the monosymmetry.
KEYWORDS = flora evolution, floral organogenesis, floral symmetry, Lecythidaceae, Lecythidoideae, monosymmetry, pollination, polysymmetry.
Multimedia:
Floral organogenesis
Floral organogenesis