Acropetally developing vascular bundles coexisting with basipetally developing and basally blindly ended vascular bundles in scapes of Eriocaulon taquetii (Eriocaulaceae, monocotyledons).

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In various monocotyledons, there are basally blindly ended stem vascular bundles, which never connect to the vascular bundles of roots. These blindly ended vascular bundles seem to be unsuitable for transferring water in terrestrial plants. In the present study, we aim to clarify the trace of the blindly ended stem vascular bundles in whole plants, and consider the evolutional process for holding such vascular bundles in the stem. We examined a whole stem vasculature of Eriocaulon taquetii (Eriocaulaceae, monocotyledons) by observation of serial transverse sections, cut by a manual rotary microtome, and viewed under an epifluorescence microscope. Our investigation revealed a threedimensional reconfiguration of the scape vasculature and detected basipetally developing and basally blindly ended vascular bundles, originated from involucral bracts and arranged with acropetally developing vascular bundles alternately in the scape internode. The basipetally developing and basally blindly ended vascular bundles, which originate from the primodia of foliar organs, have been reported in various commelinids. The characteristic vascular bundles would be homologous and presumed to be a synapomorphy of commelinids. These vascular bundles are considered to be a relic characteristic from ancestral semiaquatic plants of monocotyledons.