Evolution of the ⁷Li abundance in the envelope of a 1.5 M_⊙ and solar-metallicity RGB star, temporal evolution proceeding from left to right from the luminosity bump to the end of the RGB phase. The standard definition of the lithium abundance is here used, namely A(⁷Li) = 12+. The red solid curves represent the variation in A(⁷Li) due to the uncertainty in the TH ⁷Li(p, α)⁴He reaction rate derived here, while the black curves define the allowed region if different mixing rates (indicated by the labels in unit of 10^-7 M_⊙/yr) are used in the calculation of Palmerini et al. (2011) (see text for details). Open symbols represent the amounts of Li observed in a sample of 25 M-giants (by Luck & Lambert 1982) to compare the spread in the Li-abundance observations with uncertainties in the ⁷Li(p, α)⁴He reaction rate and mixing parameters with the spread in the observations of low mass evolved stars.