Abstract: The anatomy and histochemistry of Hydrocotyle sibthorpioides were investigated under light and fluorescence microscopy in this research. The findings were: 1) The adventitious root of H. sibthorpioides consisted of proto-xylem and proto-phloem, superceded by diarch primary vasculature of metaxymlem and metaphloem, surrounded by endodermis, then cortex, exodermis and epidermis. 2) Stolon, pedicel and leaf were primary structures with epidermis, collenchyma, cortex, endodermis, vascular bundle and pith, except that vasculature of the stolon and pedicel had secondary structures, and stolon had induced aerenchyma. 3) The apoplastic barriers in adventitious roots of H. sibthorpioides included the inner layers of endodermis with Casparian bands and suberin, the outer layers of exodermis with Casparian bands and suberin and the epidermis with suberin. The stolons, pedicels and petioles had similar apoplastic barriers, including the inner layer of endodermis with Casparian bands and suberin, and the outer layer of the cuticle, but the endodermis had no suberin in pedicels and petioles; leaf blades had only a cuticular apoplastic barrier. 4) The anatomical structure and apoplastic barrier characters are important structural determinants of adaptation of H. sibthorpioides to variably-moist environments. The implications of this research for selection of plant species to restore degraded wetlands are discussed.