, Puccinia is a genus of fungi specifically associated with causing rust diseases, such as wheat rust . The fungus responsible for smut is Ustilago . Therefore, the first pairing is wrongly matched . The other combinations are correct: roots are anatomically exarch, meaning the protoxylem is located towards the periphery ; Cassia is a noted example of a plant with imbricate aestivation ; and positive root pressure is the cause of guttation in various herbaceous plants .