AbstractMeasurements of lobe elongation of the thalloid liverwortsPallavicinia lyelliiandPellia epiphyllawere made on shaded streambanks at Silwood Park using a photographic technique. The average cumulative growth ofPallaviciniaover 12 months from 1 August 1989 was 8.7 mm compared to 24.7 mm forPellia. Monthly growth increments ofPallaviciniawere positively correlated with average air temperature and accumulated temperatures (day-degrees) in each period. Growth ofPelliawas unrelated to temperature. Neither species showed a correlation of growth with rainfall amounts or numbers of wet days, probably because thallus hydration is governed predominantly by soil wetness.Pallaviciniaappears to coexist with the more vigorousPelliaby tolerating drier niches than can be endured byPellia.Persistence ofPallaviciniaat this site may be due to the presence of both sexes and frequent colonization of fresh surfaces by spores.