Members of this family are perennial plants, with a bulb, corm or rhizome. The plants grow erect, and have leaves that are generally grass-like, with a sharp central fold. Some examples of members of this family are the Blue Flag and Yellow Flag.
The family is currently divided into four subfamilies but the results from DNA analysis suggest that several more should be recognised:
Subfamily Isophysidoideae contains the single genus Isophysis, from Tasmania. It is the only member of the family with a superior ovary and has a star-like yellow to brownish flower. Subfamily Nivenioideae contains six genera from South Africa, Australia and Madagascar, including the only true shrubs in the family (Klattia, Nivenia and Witsenia) as well as the only myco-heterotroph (Geosiris). Aristea is also a member of this subfamily. It is distinguished by having flowers in small, paired clusters among large bracts, slender styles that are divided into three slender branches and nectar (when present) produced from glands in the ovary walls. The flowers are always radially symmetrical, with separate tepals (petals) and the rootstock is a rhizome.
Subfamily Iridioideae is distributed throughout the range of the family and contains the large genera Iris and Moraea. It is the only subfamily that is represented in South America. The species have flowers in solitary clusters among large bracts, styles that are often petal-like or crested and nectar (when present) is produced from glands on the tepals. Most species have separate petals and the rootstock is usually a rhizome or rarely a bulb. The flowers are almost always radially symmetrical. Bobartia, Dietes and Ferraria belong to this subfamily.
Subfamily Ixioideae, which contains nearly two thirds of the species, is mostly African. This subfamily contains most of the familiar genera apart from Iris and Moraea, including Ixia, Gladiolus, Crocus, Freesia and Watsonia. It is easily recognised by bearing flowers in a spike-like inflorescence (sometimes solitary), with the tepals joined into a short or long tube. Nectar is produced from glands in the ovary wall and is secreted directly into the base of the floral tube. The flowers are either radially symmetrical or more usually bilaterally symmetrical and two-li