"苔藓植物学" can be translated into English as "bryology" or, more specifically, "the study of bryophytes" (though "bryology" is the more concise and commonly used term in the scientific community).
Here, "bryophytes" refers to the group of non-vascular plants that includes mosses, liverworts, and hornworts, and "bryology" is the branch of botany that focuses on their study.