Overview
The Iridaceae are a prominent family, forming characteristic components of several ecoregions such as fynbos. Genera such as Crocus and Iris are significant components of the floras of parts of Eurasia, and Iris also is well represented in North America. Gladiolus and Moraea are large genera and major constituents of the flora of sub-Saharan and Southern Africa. Sisyrinchium, with more than 140 species, is the most diversified Iridaceae genus in the Americas, where several other genera occur, many of them important in tropical horticulture.
All members of Iridaceae have petaloid, soft-textured and colorful perianths in which the three tepals of the inner whorl and the three of the outer whorl are alike in structure, shape, and often in color. This type of corolla, a feature of all families of Asparagales as well as the related order Liliales, distinguishes them from other monocots, such as grasses, palms or reeds, in which the perianth is either reduced or with the members of one or both of the whorls firm-textured and dry and often brown or green. The character that sets Iridaceae apart from other plants of the Asparagales or from the Liliales, is the male part of the flower, the androecium, which has three stamens—in most related families there are six. Another character that distinguish Iridaceae from most other members of the Asparagales is its inferior ovary, the ovary being superior in most families, with the exception of Orchidaceae and Amaryllidaceae. Apart from their flowers, the Iridaceae can usually be recognized by their characteristic leaves, sword-like and oriented edgewise to the stem and with two identical surfaces. Such leaves are termed isobilateral and unifacial. In contrast to the Irids, typical plant leaves – termed dorsiventral and bifacial – have upper and lower surfaces of different appearance and anatomy.
The Iridaceae originated in Antarctica-Australasia in the late Cretaceous, about 82 million years ago, although the family's subsequent radiation occurred elsewhere, notably in southern Africa and temperate and highland South America, at the end of the Eocene or later.
Currently, 66 genera are recognized, which are distributed among 7 subfamilies and occur in a great variety of habitats. Most species are adapted to seasonal climates that have a pronounced dry or cold period unfavourable for plant growth, during which the plants remain dormant. As a result, most species are deciduous, in that their above-ground parts (leaves and stems) die down when the bulb or corm enters dormancy. The plants thus survive periods that are unfavourable for growth by retreating underground. Evergreen species are restricted to subtropical forests or savannah, temperate grasslands and perennially moist fynbos.
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