We studied the responses of gas exchange, leaf morphology, and growth to irradiance in Taihangia rupestris, a naturally rare herb inhabiting only vertical cliff faces. In low irradiance (LI, 10 % of full sun) T. rupestris had lower net photosynthetic rate (PN) and produced much less leaves, total leaf area, and biomass than in high (HI, full sun) or medium irradiance (MI, 50 % of full sun). PN of T. rupestris was higher in HI than in MI on August 8, but lower in HI than in MI on September 22. T. rupestris had shorter petioles and lower leaf area ratio, and produced more but smaller and thicker leaves in HI than in MI. In HI the fast production of new leaves may guarantee T. rupestris to maintain higher PN at the whole plant level and thus accumulate more biomass at harvest, although the single-leaf PN may become lower as found on September 22. Hence T. rupestris possesses a latent capacity to acclimate and adapt to full sun. Irradiance, therefore, may not be a responsible factor for the restricted distribution of T. rupestris on vertical cliffs. and Min Tang ... [et al.].