Data from flowering plants of Cerastium fontanum recorded in 2017 and 2018 in Hengill, a sub-arctic geothermal area in SW-Iceland (64°03’N; 21°18’W, ~360 m.a.s.l.)

This data set includes 2 years of data on flowering phenology and fitness of the perennial herb Cerastium fontanum, as well as temperature data recorded at the location of each plant. The data includes information for 245 flowering individuals in 2017, and for 104 individuals in 2018.