Iris Family

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Iris Family

Irises are plants in the family Iridaceae, which contains 1,500-1,800 species and 70-80 genera. The center of diversity of this family is in southern Africa, but species are found on all of the habitable continents. The largest groups in the family are the true irises (Iris spp.) with 200 species and gladiolus (Gladiolus spp. ) with 150 species.

Many species in the iris family have large, attractive flowers. The major economic importance of this family involves the cultivation of many species in horticulture. In France and Quebec the iris is generically known as the fleur-de-lis, and it is an important cultural symbol.

Biology of irises

Most species in the iris family are perennial herbs. These plants die back to the ground surface at the end of the growing season and then redevelop new shoots from underground rhizomes, bulbs, or corms at the beginning of the next growing season. A few species are shrubs.

The leaves of iris species are typically long, narrow, and pointed at the tip with parallelveins and sheathing at the base of the plant or shoot. The large, colorful,

showy flowers are erect on a shoot and contain both female (pistillate) and male (staminate) organs.

The floral parts are in threes: three petals, three sepals, three stamens, and a pistil composed of three fused units. The sepals are large and petal-like, and they enclose the petals which are erect and are fused into a tube-like structure in some species. The flowers may occur singly or in a few-flowered inflorescence, or cluster. The flowers produce nectar, are pleasantly scented, and are pollinated by flying insects or birds, although some species are wind-pollinated. The fruits make up a three-compartmented capsule containing numerous seeds. The leaves and the rhizomes of Iris species contain an irritating chemical which is poisonous if eaten.

Native species of North America

Various species in the iris family are native to wild places in North America. Wild irises are most commonly found in moist habitats beside lakes, ponds, rivers, and seashores. Some of the more widespread species of iris include the blue-flag (Iris versicolor ), violet iris (I. verna ), water flag or western blue flag (I. missouriensis ), western iris (I. tenax ), and the beachhead-iris (Iris setosa ). Another widespread group in the iris family is the blue-eyed grasses, for example, Sisyrinchium montanum. The blue-eyed grasses are found in a wide range of moist habitats and sometimes beside roads and other disturbed places.

Horticultural irises

Many species and cultivars in the iris family are grown in gardens and greenhouses for their beautiful flowers. These plants are typically propagated by splitting their rhizomes, bulbs, or corms, and sometimes by seed.

Various species of iris are cultivated in gardens. These include the yellow-flowered water-flag (Iris pseudacorus and blue-flowered species such as the true fleur-de-lis (I. germanica ), the Siberian iris (I. sibirica ), the stinking iris (I. foetidissima ), and the butterfly iris (I. ochroleuca ). Some cultivated species of iris have become naturalized in parts of North America and can be found in wild habitats and in old gardens near abandoned houses.

Many of the approximately 80 species of crocuses are grown in gardens. In places where there is a snowy winter, crocuses are often bloom very soon after the snow melts and air temperatures become mild. The most commonly cultivated species is the European spring crocus (Crocus verna ).

Another commonly cultivated group is the gladiolus, including Gladiolus byzantinus from southwestern Asia and many horticultural hybrids. The tiger flower (Tigridia pavonia ) is native to Mexico and is sometimes cultivated in temperate gardens.

Other economic products

The world’s most expensive spice is said to be saffron, a yellow substance made from the blue-flowered saffron crocus (Crocus sativa ) of the eastern Mediterranean region. The major expense of saffron is in labor costs because it takes the floral parts 600-800 crocus flowers to make 0.035 oz (1 dry gram) of the spice. Saffron is used mainly to flavor and color foods, as in saffron rice.

The rhizomes of the orris (Iris florentina ) are used to manufacture perfumes and cosmetics. The rhizomes must be peeled and dried before their odor, much like that of violets (Viola spp.), will develop.

KEY TERMS

Bulb —An underground thickened stem with many fleshy leaves surrounding a bud and fibrous roots emerging from the bottom. New shoots develop from bulbs at the beginning of the growing season.

Corm —A thick broad vertically growing underground stem that is covered with papery leaves and from which new shoots develop at the beginning of the growing season.

Cultivar —A distinct variety of a plant that has been bred for particular, agricultural or culinary attributes. Cultivars are not sufficiently distinct in the genetic sense to be considered to be subspecies.

Inflorescence —A grouping or arrangement of florets or flowers into a composite structure.

Rhizome —This is a modified stem that grows horizontally in the soil and from which roots and upward-growing shoots develop at the stem nodes.

Stigma —The part of the female organs of a plant flower (the pistil) upon which pollen lands in the first stage of fertilization.

Style —A stalk that joins the pollen-receptive surface of the stigma, to the ovary of the female organ of a plant (i.e., the pistil). Fertilization actually occurs in the ovary, which is reached by the male gametes through growth of an elongate pollen-tube from the pollen grain.

Resources

BOOKS

Judd, Walter S., Christopher Campbell, Elizabeth A. Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.

Klein, R. M. The Green World: An Introduction to Plants and People. New York: Harper and Row, 1987.

Raven, Peter, R. F. Evert, and Susan Eichhorn. Biology of Plants. 6th ed. New York: Worth Publishers Inc., 1998.