To address the challenge of simultaneously achieving a low peak-to-average power ratio (PAPR), high power efficiency, and low receiver complexity in existing hybrid optical orthogonal frequency-division multiplexing (O-OFDM) schemes for wireless optical communications, a novel constellation-extension-based low-PAPR hybrid pulse-amplitude-modulation discrete multitone (LP-HPAM-DMT) scheme is proposed. In the proposed scheme, each original PAM symbol is expanded into multiple equivalent constellation points. A composite performance metric is formulated to jointly optimize PAPR reduction and power-efficiency enhancement, and a stepwise constellation-extension algorithm is developed for iterative optimization. At the receiver, the effect of constellation extension is eliminated via a low-complexity modulo operation, thereby preserving the inherent low-complexity advantage of conventional HPAM-DMT. Simulation results demonstrate that LP-HPAM-DMT achieves a lower PAPR than existing methods and provides improved bit error rate (BER) performance as well as higher power efficiency under both linear and nonlinear transmission conditions.