The main aim of this study was to investigate if the charophyte species Chara baltica, Chara canescens (two populations from the Baltic Sea (BS) and the Gulf of Korinth, Greece (GK)), and Lamprothamnium papulosum exhibit different acclimation capacities to irradiance. Growth, photosynthesis and pigment content were examined in the laboratory under six irradiance conditions (35-500μmol photonsm - 2 s - 1 ). Growth experiments showed increasing growth rates from 35μmol photonsm - 2 s - 1 (~10mg fresh weight (FW)) up to 70μmol photonsm - 2 s - 1 (~20mg FW) in C. baltica, from 35μmol photonsm - 2 s - 1 (~15mg FW) up to 380μmol photonsm - 2 s - 1 (~145mg FW) in C. canescens (BS), and up to the highest growth irradiance in algae of L. papulosum (35μmol: ~5mg FW; 500μmol: ~20mg FW). The species were tested for their ability to acclimate to different growth irradiances (E g ) by calculating P m a x (maximum photosynthesis rate at saturating irradiances), α (the efficiency of light utilization at limiting irradiance), and E k (the light saturation point of photosynthesis, P m a x /α). All species exhibited increasing P m a x with increasing E g . Whereas both populations of C. canescens increased α with increasing E g , L. papulosum and C. baltica did not acclimate α at all. E k , the irradiance at which photosynthesis ceased to be light-limited, was constant for all Chara species within the range of irradiances tested. Chl a/Chl b ratios of all species were constant over the whole range of E g . Chl a/carotenoid ratios were constant in C. baltica, whereas Chl a/carotenoid ratios in L. papulosum and C. canescens (BS) decreased from 250 and 70μmol photonsm - 2 s - 1 upwards, respectively. Pigmentation analysis showed that Chl a/carotenoid acclimation was mainly caused by species-specific capacity to raise the content of lutein and carotene (C. canescens (BS), C. canescens (GK)) and xanthophyll cycle pigments (XCP; L. papulosum). The non-photochemical quenching (NPQ) capacities of L. papulosum, C. canescens (BS), and C. canescens (GK) were dependent from preacclimation status of algae, whereas NPQ of C. baltica was independent from growth irradiance.Our results indicate that C. baltica and C. canescens (BS) were light saturated within the chosen irradiances, whereas C. canescens (GK) and L. papulosum did not reach their limits of high-light acclimation. The photosynthetic pigments lutein, α- and β-carotene are suggested to act as photo-protective pigments in L. papulosum and C. canescens.