Flora of North America species comparison

Genera ca. 65, species ca. 1810 (16 genera, 92 species; 9 genera, 19 species introduced, and various hybrid complexes in the flora).

Iridaceae are currently divided into four subfamilies (P. Goldblatt 1990, 1991). Subfamily Isophysidoideae Takhtajan is monotypic, comprising the Tasmanian Isophysis T. Moore with a superior ovary. Only subfamily Iridoideae is native in North America. The remaining Nivenioideae Schulze ex Goldblatt and Ixioideae Klatt are centered in Africa south of the Sahara. Iridaceae are of considerable economic importance in ornamental horticulture and the cut-flower industry, especially Iris, Gladiolus, and Freesia. Several other genera (e.g., Crocus, Dietes, Sparaxis, Tritonia, Watsonia) are cultivated in gardens in both tropical and temperate areas. Moraea and Homeria are poisonous and pose significant problems in cattle- and sheep-raising areas, notably in southern Africa.

In addition to the several genera and species escaped from cultivation and dealt with in detail below, the following are widely grown in areas of mild winter and may persist in and near abandoned gardens, sometimes reproducing successfully: Dietes Salisbury [D. iridioides (Linnaeus) Salisbury ex Klatt, D. grandiflora N. E. Brown]; Ixia Linnaeus (I. maculata Linnaeus, I. polystachya Linnaeus); Crocus cultivars and even some wild species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 280 (34 in the flora).

Because irises have large, handsome flowers, have many different forms, colors, and color patterns, and are easily grown and propagated, they have become popular garden ornamentals. Many non-native irises may be found in the flora area, not only in specialized gardens, but in casual plantings and persisting around old dwellings, in cemeteries, and along roadsides. These include not only the more common bearded irises, but members of the Sibirian, Spuria, Japanese, and Dutch groups. In the Pacific Coast and southeastern areas of the flora, repeated hybridization, both natural and artificial, of some of the local species has produced hundreds of garden forms that have added greatly to the popularity of this genus. Asexual reproduction in many Iris species may be more important than sexual reproduction in their persistence, and many hybrid clones may persist for decades in sites no longer cultivated.

The species of Iris differ from members of other native genera of the Iridaceae in North America in three ways: 1) the sets of outer and inner perianth members (sepals and petals herein) differ from each other in shape, orientation, and, in some cases, coloration; 2) the parts of the flowers—petals, sepals, stamens, and styles—are united basally into a floral tube that surmounts the ovary; and 3) the styles are petaloid and modified with some specialized structures to insure cross pollination.

T. Holm (1929) restricted the term rhizome to a horizontal, usually subterranean, stem that produces roots from its lower surface and green leaves from its apex, developed directly from the plumule of the embryo. He recognized stolons as axillary, subterranean branches that do not bear green leaves but only membranaceous, scalelike ones. The rhizomes of Iris are of two basic kinds: homogeneous, with the branches like the primary one in size and texture, and heterogeneous, with the branches of the primary rhizome like stolons with scalelike leaves. These enlarge at the apex to produce green leaves and more stolonlike branches.

According to B. Mathew (1990), Iris includes six subgenera. Species of subgenera Iris and Limniris are rhizomatous; the others are either bulbous or perennial from a fascicle of fleshy roots. Three species of subg. Iris are sometimes found naturalized from cultivation in the flora area. Other species of the subgenus are found here only in cultivation or as waifs. The native North American species of Iris all belong to subg. Limniris, usually referred to as the beardless irises. The four other subgenera, which are found in the flora area only in cultivation or as waifs, have all been recognized sometimes as separate genera: subg. Nepalensis (Dykes) Lawrence as Junopsis Schulze; subg. Xiphium (Miller) Spach as Xiphion Miller; subg. Scorpiris Spach as Juno Trattinnick; and subg. Hermodactyloides Spach as Iridodictyum Rodionenko. F. Köhlein (1987) accepted these four segregate genera; however, most current authors circumscribe Iris in the broad sense, as here.

Elevation is unimportant in the taxonomy and ecology of Iris, and very rarely is it recorded on specimen labels. Consequently, elevations are not reported in the species treatments that follow.

(Discussion copyrighted by Flora of North America; reprinted with permission.)