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The A4 isoform of the bark lectin RPbAI from Robinia pseudoacacia has been crystallized in two different crystal forms. Crystal form I grows in the P21 space group with two tetramers in the asymmetric unit, whereas crystal form II grows in the I222 space group with a monomer in the asymmetric unit. Data sets were collected for both crystal forms to resolution limits of 2.55 and 1.81 Å, respectively, which will allow successful structure determinations.