Water is essential for all life but while most studies focus on liquid water, few studies focus on water vapor. The amount of water vapor is informative of the habitat and can provide an organism information on the favorableness of a habitat. Plant species where individuals vary along moisture gradient are good candidates to test for variation in a trait’s response to relative humidity. In the liverwort Marchantia inflexa, water stress responses differ by the sex of the plant and vary across habitats differing in moisture levels. Further, germination responses are critical for successful establishment of populations. To test for differences in M. inflexa germination responses due to water vapor, asexual propagules were floated on water and exposed to air with high (100%) or low (65%) relative humidity (RH). Twenty female and male laboratory-grown M. inflexa plants from two locations (East Turure (high moisture) and North Oropuche (low moisture)) in Trinidad and Tobago were used in this study. Germination was measured after one day. Four trials were completed. Germination was significantly higher in high RH compared to low RH, significantly higher in plants from the drier, more exposed habitat compared to plants from the moist, less exposed habitat and, the sexes did not differ. Despite floating on liquid, the lower RH reflects less optimum moisture conditions. Higher germination in plants from the less mesic relative to more mesic habitat suggests selection for quicker germination response when conditions are favorable. This finding is evidence that genetic variation occurs in M. inflexa response to water vapor. Response to water vapor is a critical response where the sensors remain unknown.