A large group of flowering plants (angiosperms) that for many years has been considered one of the two main categories of plants, the other being monocotyledons. Dicotyledons have two seedling leaves as opposed to the single one in most monocotyledons. Several deoxyribonucleic acid (DNA) sequence studies subsequently demonstrated that there are two groups of angiosperms, but these correspond not to the number of seed leaves but to the two major pollen types. Thus, the term "dicotyledon" is no longer meaningful because some plants of this type are more closely related to monocotyledons. The group of former dicotyledons, which have pollen with a single aperture, includes magnolia, avocado, black pepper, and pipeworts; they are now termed magnoliids and include monocotyledons. The other category of dicotyledons, those with three (and often more) apertures in their pollen, are called eudicotyledons (true dicotyledons).