Article

Pattern and significance of seedling development in Titanotrichum oldhamii (Gesneriaceae)

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Abstract

The seedling development of Titanotrichum oldhamii (Hemsl.) Solereder has been investigated to provide insight into the evolution and systematic position of Titanotrichum. In T. oldhamii, the size differentiation of the two cotyledons begins while the hypocotyl grows. However, both of the two cotyledons develop normally and locate at the same level. Finally, the two cotyledons are almost equal in size. The aerial shoot (including stem and leaves) is produced from the permanent activity of the apical meristem in the plumular bud. Even though the seedling development in Titanotrichum basically conforms to the general growth pattern of the seedling in the Cyrtandroideae, it is remarkably different from that of other Cyrtandroideae. Based on the revealed evidence in seedling development in Titanotrichum and other comparative data, the authors have evaluated the possible evolutionary pathway of Titanotrichum and further discussed the familial placement of this genus.

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... However, no previous study has addressed the origin of the habit in epiphytic lineages represented by species in these rainforests. Among the vascular epiphytes of Chilean temperate rainforests, three endemic monotypic genera of Gesneriaceae belong to the Coronanthereae (Smith et al., 1997;Wang et al., 2002;Mayer et al., 2003) and are frequent components of the canopy. Asteranthera ovata (Cav.) ...
... BIOGEOGRAPHIC AND PHYLOGENETIC DATA FOR CORONANTHEREAE Available phylogenetic (Smith et al., 1997;Wang et al., 2002;Mayer et al., 2003), systematic, ecological, biogeographical, and morphological information for the species in the Coronanthereae (Bentham, 1869;Reiche, 1898;Petrie, 1903;Guillaumin, 1948;Allan, 1961;Morley, 1978;Morley & Toelken, 1983;Wiehler, 1983;Nicholson & Nicholson, 1991;Walsh & Entwisle, 1999;Friedman et al., 2004) ...
... Phylogenetic studies and isocotylous seedlings support the position of the Coronanthereae within the Gesnerioideae (Burtt, 1963;Smith et al., 1997;Wang et al., 2002;Mayer et al., 2003) in a fairly basal position (Wang et al., 2002). Our literature review indicated a diversity of growth habits among living species of Coronanthereae, varying from trees to holoepiphytes. ...
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... isocotylous in the Gesnerioideae). Anisocotyly is not simply a size difference of the cotyledons due to a different growth tempo of the two structures (as misinterpreted for Titanotrichum in Wang et al. 2002), but involves a characteristic set of features (see Burtt 1970, Jong 1970). Size differences, even culminating in the complete reduction of one of the two cotyledons, do occur in other angiosperm families as well (e.g., Ranunculaceae, Cyclamen L., see Hill 1938), but the situation in Gesneriaceae is quite different (see also Nishii et al. 2004, Mantegazza et al. 2007). ...
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... All other Old World Gesneriaceae show anisocotyly involving the persistent growth of a macro-cotyledon (Jong 1973;Jong and Burtt 1975), but Titanotrichum is isocotylous ( Wang and Cronk 2003). A recent report of anisocotyly in Titanotrichum ( Wang et al. 2002) appears to refer to cotyledon asymmetry upon germination rather than a persistent meristematic activity. The isocotyly of Titanotrichum is consistent with our placement of the genus with the isocotylous New World Gesneriaceae. ...
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