Greenhouse tomato cultivation often requires a high energy input to maintain set-point temperatures. If set-point temperatures could be lowered by a few degrees this would reduce energy consumption significantly. However, this can only be applied when new, more energy-efficient cultivars are developed, i.e. cultivars that can be cultivated at sub-optimal temperatures without loss of production or quality. As variation for temperature response within the current elite tomato cultivars is limited, it is important to look for other sources of variation. One option are wild relatives which originate from South America, where they grow at altitudes up to 3300 m. In this study we examined the effects of temperature (12¿24°C) on growth of young vegetative tomato plants of the cultivar `Moneymaker¿ and two wild relatives (L. hirsutum LA 1777 and L. pennellii LA 716). The aim was to elucidate the physiological and morphological parameters which underlie interspecific differences in growth response to sub-optimal temperatures. During a 28-day period five destructive measurements were carried out in which total dry weight, including root weight, leaf area and leaf dry weight were measured in order to calculate growth parameters. Even though `Moneymaker¿ had a higher relative growth rate (RGR) over a large temperature range (16¿24°C), RGR of `Moneymaker¿ was severely reduced below 20°C, while RGRs of L. hirsutum and L. pennellii were only decreased below 16°C. At 12°C RGR of `Moneymaker¿ was reduced by 41% compared to 20°C, while in L. pennellii and L. hirsutum this decrease was only 27 and 18%, respectively. This decrease in RGR in `Moneymaker¿ was mainly a result of a decreased leaf area ratio (LAR), caused by a 35% decrease in specific leaf area (SLA). In contrast, the decrease in RGR in L. pennellii and L. hirsutum was a result of a decreased net assimilation rate (NAR) of 24 and 14%, respectively. This study illustrates that wild tomato species provide possibilities for the breeding of more energy-efficient tomato greenhouse cultivars