Leucaena [Leucaena leucocephala (Lam.) de Wit] is a perennial weed in more than 25 countries, including Australia. Knowledge regarding the seed biology of L. leucocephala could help in making weed management decisions. Experiments were conducted to study the effect of hot water (scarification), alternating temperatures, heat stress, salt stress, water stress, and burial depth on seed germination of two populations of L. leucocephala collected from Toowoomba and Gatton, Australia. The optimum duration of hot water treatment to break the hard seed coat dormancy was 2 min for both populations. The highest germination (92% to 98%) was recorded at 35/25 C for both populations, and similar germination occurred at 30/20 C. The Toowoomba population recorded greater germination at low temperature (15/5 to 25/15 C) than the Gatton population. Additionally, the Gatton population had higher germination than the Toowoomba population after 5 min of exposure to temperatures of up to 100 C, suggesting that the Gatton population may be more tolerant to heat stress. Germination was completely inhibited at pretreatment (5 min) temperatures of 150 to 250 C. The Toowoomba population recorded 17% greater germination than the Gatton population at a high salt concentration (160 mM NaCl), indicating its greater salt tolerance. At low moisture stress (–0.1 and –0.2 MPa), higher germination was observed in the Toowoomba population than in the Gatton population, whereas germination was similar for both populations at higher water stress levels (–0.4 MPa or lower). Germination was similar for both populations at shallow depths (0 and 1 cm) but higher emergence was recorded for the Toowoomba population at 2 to 8 cm than the Gatton population. Differential germination behaviors of both populations suggest that they adapted differently in their respective local environments. Knowledge gained from this study will help in formulating integrated management practices for L. leucocephala.