Fern (Pterisvittata L.) fronds were collected in the Reppel small-scale field experiment aiming at arsenic phytoextraction. Three organic fractions, i.e. holocellulose, hemicelluloses, and lignin, were extracted from the fronds. The frond biomass as well as the holocellulose, hemicelluloses, and lignin fractions were converted by sub- and supercritical water treatments at low temperatures, 300 °C and 400 °C with 25 MPa, and organic products were identified. This study highlighted that hemicelluloses and lignin are reported as the major sources of cyclopentenones and furfurals, 5 carbons-containing products. The degradation of carbohydrates part (holocellulose and α-cellulose) provided the largest range of by-products due to the thermal resistance of the lignin. The control of biochemical families's content and temperature should determine the presence of required by-products. The fact that no 'synthetic' materials but original materials, i.e. holocellulose, α-cellulose and lignin directly extracted from control fern fronds have been converted revealed the presence of benzenes and cyclopentenones, by-products which have not been reported by the literature.