The Collaborative International Dictionary of English v.0.48:

Algology \Al*gol"o*gy\, n. [L. alga seaweed + -logy.] (Bot.)
   The study or science of alg[ae] or seaweeds.
   [1913 Webster]

WordNet (r) 3.0 (2006):

algology
    n 1: the branch of botany that studies algae [syn: phycology,
         algology]