Aims: Cyperaceae are common on nutrient-poor soils, including in western Japan. We examined the ability of the native Cyperaceae from western Japan to form dauciform roots and assessed the potential resulting contribution to soil phosphorus (P) dynamics. Methods: We assessed dauciform roots for 28 native Cyperaceae. Shoots, roots (including dauciform roots), and bulk and rhizosheath soils of Carex lenta were collected in Seto Inland Sea district (western Japan). The number of dauciform roots, shoot P and nitrogen (N) concentration, and soil P status and fractions were analyzed. Results: We confirmed dauciform-root formation in many Cyperaceae including the genus Carex. The number of dauciform roots of C. lenta showed a negative correlation with total and available soil P concentrations and with shoot P concentration. In the rhizosheath of C. lenta with many mature dauciform roots, we found an increase of readily-available inorganic P (Pi) and a decrease of readily-soluble organic P and sparingly soluble Pi fractions, indicating that the dauciform roots contributed to the acquisition of poorly-available soil P. Conclusions: Our results show negative correlations of the number of dauciform roots with both soil and plant P status. Regosols with a low P availability are common in Seto Inland Sea district; thus the formation of dauciform roots and their exudates induced by low P status are important for the distribution of C. lenta in this region.