Simple models of the growth and development of legume cover crops in different environments may aid the selection of species and genotypes most suitable for particular farming systems. The effects of temperature and photoperiod on the daily rate of seedling emergence (1/t50%) and the rate of leaf appearance (leaves d⊃−1&/sup;) were quantified for 12 diverse legume cover crop species. Six tropical or subtropical species were grown in 12 combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (11.5, 12.5, 13.5 and 14.5 h d⊃−1&/sup;). Another six genotypes of temperate species were grown in nine combinations of mean temperature (16.8, 21.8 and 26.8 °C) and photoperiod (12.5, 13.5 and 14.5 h d⊃−1&/sup;). Durations from sowing to 50% seedling emergence (t50%) were recorded and the number of leaves on the main stem counted during early vegetative growth. Photoperiod did not affect either 1/t50% or leaves d⊃−1&/sup;. However, the effects of temperature, photoperiod response group (short-day or long-day response), genotype or species and their interactions were all significant. An optimal temperature between 21.8 and 26.8 °C for leaves d⊃−1&/sup; was identified for Vicia sativa, Vicia dasycarpa and Lupinus mutabilis. Below the optimum temperature, 1/t50% and leaves d⊃−1&/sup; were positive linear functions of temperature for all legume species except Vicia dasycarpa. Estimates of base temperature (Tb) and thermal time (θ) for 1/t50% and leaves d−1 were obtained for each legume cover crop from these functions. Common values of Tb were found within each photoperiod response group: 9 °C and 1 °C for 1/t50%, and 10 °C and −2 °C for leaves d⊃−1&/sup; for short-day and long-day species respectively. Differences among species were represented by variant estimates of θ. The practical consequences of the combined effects of these values of Tb and θ for selecting legume cover crops for particular farming systems are discussed.