1929, Iris Atrocyanea
Addisonia volume 14, page 13, plate 455, 1929
Native of southern Louisiana
Family Iridaceae, Iris Family
Among such a variety of colors and shades of color as are exhibited by the irises of the Lower Mississippi Delta it is difficult to decide which species has the most striking flowers. The pleasing element in the flower of the dark-blue iris that attracts the eye most promptly is the sharp contrast of two very decided colors, the narrow light-yellow or golden crest in the base of the very dark-blue sepal-blade. In most of the species there is an area of modified coloration between the crest and the dominant color of the sepal-blade, but in this case that feature is lacking. The colors are similarly contrasted in the sepals of Iris vinicolor.
The geologic and the geographic history of Iris atrocyanea is as obscure as that of many of its associates. Its ancestors certainly did not grow in the region to which it is now confined, for the lower Mississippi Delta has been quite recently laid down, geologically speaking. Why such gorgeous forms as now exist in southern Louisiana, or their ancestral forms, did not migrate to the Atlantic seaboard, or if they did why they subsequently disappeared is difficult to understand. That this species has been accustomed to a cooler climate than that of its present area of distribution is indicated by the fact that plants are hardy in the cold-frames at The New York Botanical Garden although thoroughly frozen in the winter. They are also hardy in the open with slight protection during the most severe winter weather.
Iris atrocyanea grows naturally equally as well in the open and in partial shade. Swamps and ditches under Cypress trees where water stands for long periods are its delight and marshes with a thin turf of grasses and small herbaceous plants support a luxuriant growth. The type specimen is in the herbarium of The New York Botanical
The dark-blue iris has a stout branching fleshy rootstock. The leaves are erect, three to five together at the base of the flower-stalk. The blades are narrowly linear-attenuate, usually three-quarters to one inch wide, deep-green. The flower-stalk is erect, two to three feet tall, with one or two flower-bearing nodes below the terminal, the internodes slightly flattened, especially below the bases of the leaf -like bracts where they are usually sharply angled. The involucre is erect, of two or three main bracts, the outer bract lanceolate-attenuate, exceeding the flower, slightly keeled on the back, narrowly scarious margined, the inner (second) bract about equalling the base of the perianth, with a soft scarious tip. The flowers are usually paired at the tip of the flower-stalk, and single or paired in the axils of the leaf-like bracts below. The hypanthium covering the ovary is six-angled, together with the pedicel rather loosely enveloped by the involucre. The fiower-tube is nearly cylindric, as long as the ovary. The three sepals are remate, two and three-quarter to three and three-quarter inches long, arching. The claw is shorter than blade, slightly narrowed to the base; without, green and obscurely striate ; within, mainly green or yellowish-green, and green-striate on both sides of the prominent midridge, and also with short magenta striations curving out to the margins. The blade is orbicular-oval to orbicular-ovate, longer than the claw, obtuse or notched at the apex ; without, dull violet-blue with darker veins; within, dark violet -blue and velvety, except the narrow bright-yellow or golden short-bearded crest at the base and the darker-almost black-line beyond the crest and the blackish fine veins. The three petals are somewhat shorter than the sepals, broadly spatulate. The claw is cuneate, somewhat shorter than the blade, involute at the base ; without, mainly green, except the striate magenta margins; within, finely striate-ridged and magenta-tinted above the green or yellowish base. The blade is elliptic or oval-elliptic, longer than the claw, usually notched at the apex; without, rather dull deep violet-blue; within, bright deep violet-blue and sparingly darker- veined. The three stamens are about an inch and a half long. The filaments are greenish-yellow. The anthers are linear-lanceolate, white, longer than the filaments, sagittate at the base, usually acute or acutish at the apex. The three style-branches are linear-cuneate, about one and a half inches long, concave ; without, magenta-purple, except the paler margins ; within, magenta, paler on the sharp keel and the scarious erose margins which are sometimes sharply toothed near the base. The style-appendages are half-ovate, one half to three-quarters of an inch long, magenta, unevenly toothed on the outer side and at the tip. The stigma is two-lobed, whitish, the lobes finely erose-toothed. The capsule is ellipsoid or nearly so, about three inches long, bright-green and glaucescent, more or less prominently three-sided, the ridges flat or slightly concave, with more or less of a groove, the lobes (angles) rounded, flat, or slightly grooved, thus making the capsule somewhat six-angled. The seeds are numerous, in two rows in each cavity, somewhat over a half inch in diameter, irregularly half -orbicular, very unequal in thickness, brown, corky -walled.
John K. Small
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