Comparative leaf development ofOsmunda lancea andO. japonica (osmundaceae): Heterochronic origin of rheophytic stenophylly |
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Authors: | Ryoko Imaichi Masahiro Kato |
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Institution: | (1) Faculty of Agriculture, Tamagawa University, 6-1-1 Tamagawagakuen, Machida, 194 Tokyo, Japan;(2) Botanical Gardens, Faculty of Science, University of Tokyo, 3-7-1 Hakusan, 112 Tokyo, Japan |
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Abstract: | Comparative development of the narrow pinnules of rheophyticOsmunda lancea and of the broad pinnules of a related dryland species,O. japonica, was examined and the origin of rheophytic stenophylly was discussed. The mature leaves and their various parts ofO. lancea are smaller and narrower than those ofO. japonica. The young pinnules ofO. lancea at the initiation of cell expansion are smaller than those ofO. japonica. The growth pattern of the pinnules is fundamentally the same in the two species, but pinnule growth period is shorter inO. lancea than inO. japonica. While the largest growth rate in pinnule length is quite similar, inO. lancea the pinnules are less elongated and much less broadened during ontogeny. Cell expansion in the mesophyll and epidermis proceeds
acropetally and toward the margin along the axes of costules and veins. Although the numbers of mesophyll and epidermal cells
between two adjacent veinlets are almost the same inO. lancea andO. japonica, during the subsequent growth period inO. lancea, the cells expand to a smaller extent and the veinlets become more narrowly oblique to the costule. This oblique distortion
of laminar segments framed by veins causes stenophylly, an allometric modification. The stenophylly ofO. lancea is believed to have arisen by heterochronic evolution, in particular, progenesis. |
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Keywords: | Development Heterochrony Osmunda lancea Rheophyte Stenophyll |
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