Flora of North America species comparison

The ecological range of Iris missouriensis is probably more varied than that of any other North American species of the genus, extending from almost sea level in southern California to 3000 m in Montana and Wyoming. There is correspondingly wide variation in a number of characters, which has caused much confusion as to taxonomic circumscription. Homer Metcalf (pers. comm.) made a detailed study of this species. The basic requirement for its success seems to be an extremely wet area before flowering and then almost desertlike conditions for the rest of the summer.

In large populations, sometimes covering hundreds of acres, Iris missouriensis may be found with either simple or branched stems, leaves from 4 mm to more than 1 cm wide, shorter than the stem or longer, only one flower to as many as three on a stem, and colors from deep blue to almost pure white. A single plant found on the Pariah Plateau in Kane County, Utah, with leaves only 3–4 mm wide and a single flower stem only 4 cm long, which meant that the flower was at almost ground level, was named Iris pariensis. No other such specimen has been located, and this entity must be considered as just an aberrant form that was due to the desertlike conditions in which it was growing.

Iris missouriensis is known to hybridize with I. longipetala.

(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.)