1929, Iris Giganticaerulea

Addisonia volume 14, page 5, plate 451, 1929


Big Blue Iris

Native of the Mississippi Delta

Family Iridaceae, Iris Family

Iris giganticaerulea Small, sp.nov.

While driving along the bayous and canals between New Orleans and Houma, Louisiana, about dusk on April 9th, 1925, a blue iris was several times observed growing on the water's edge. Little attention was paid it, as we were making haste to reach the Rio Grande and western Texas. The iris' flowering season was nearly past, and casual observation suggested that the plant might represent Iris Kimballiae of northern Florida. But closer acquaintance with the plant seen on the trip referred to proved it to be quite different from any previously described species.

Although specifically well isolated, Iris giganticaerulea has taxonomic associates which collectively indicate a common ancestor. This presumably grew in the southeastern highlands during the latest general submergence of the continent, in the Tertiary Period. As the land later became elevated, descendants took different courses, radiating into the Coastal Plain through a sector of about a quarter circle. Thus we now find Iris rivularis in the Atlantic Coastal Plain in Georgia and northeastern Florida; Iris savannarum in the peninsular Florida Coastal Plain; Iris Kimballiae in the East Gulf Coastal Plain ; and Iris giganticaerulea in the Mississippi Delta. If this theory of migration be correct, it is curious to notice that the two descendents that have migrated the greater distance have developed into the most showy plants — with the largest flowers and the largest fruits. As far as we know, this iris left no evidence in the trail it may have followed, however, for at present it is not known outside of the lower part of the Mississippi Delta. In its native habitat it grows mostly in the open and thrives best without any shade. Its rootstocks are usually imbedded in the soil that also supports a turf of grasses and sometimes asters.

The specimen from which the accompanying illustration was made was collected near Morgan City, Louisiana, by Charles A. Mosier and the writer on April 19, 1927. Plants survived the following winter at The New York Botanical Garden and flowered copiously in June, 1928. That this plant and its associated species of the lower Mississippi Delta can withstand the low temperatures of a climate a thousand miles north of their present habitats seems to indicate that they once had a more northern distribution. The type specimen is in the herbarium of The New York Botanical Garden.

The big blue iris has a very stout fleshy branching rootstock. The leaves are erect, mostly four to six together at the base of the flower-stalk, firm. The blades are linear-attenuate, mostly an inch to an inch and a half wide, bright green and more or less glaucescent. The flower-stalk is erect, usually two and a half to four feet tall, rather stout, with usually two or three flower-bearing nodes below the terminal, the internodes rather prominently ridged or angled below the bases of the leaf -like bracts. The involucre is erect, of usually three main bracts, the outer bract narrowly lanceolate-attenuate, exceeding the flower, keeled along the back, with a very narrow pale margin, the inner (second) bract about equalling the base of the perianth with broad translucent scarious margins. The flowers are usually in pairs at the top of the stalk, and single or paired in the axils of the foliaceous bracts below. The primary terminal flower has a narrow-columnar pedicel one and a half to two inches long, nearly terete. The hypanthium covering the ovary is shorter than the pedicel, bluntly six-angled, bright-green, and together with the pedicel tightly enclosed in the involucre. The flower-tube is cylindric-prismatic, somewhat shorter than the ovary, with nine ribs and grooves. The three sepals are remate, three and three-quarters to four and a half inches long. The claw is broad, concave, somewhat narrowed to the base below the middle; without, light-green, several ridged and striate; within, with a yellowish green body and v he ridge prolonged into a yellow crest in the base of the blade and with two or three lateral ridges which run into the yellow blotch in the base of the blade. The blade is broadly oval or orbicular-oval, longer than the claw; without, with a whitish and veined central area and bluish marginal area; within, mainly violet-blue with white streaks and flecks bordering the yellow blotch and more or less distinctly, but faintly flecked with white throughout. The three petals are somewhat shorter than the sepals, broadly spatulate. The claw is narrowly cuneate, involutely folded near the base; without, white or greenish-white at the base, violet-tinged and striate towards the blade; within, more prominently striate with greenish-brown near the base, violet-striate above. The blade is much longer than the claw; without, dull violet-blue and dark-veined; within, bright-violet-blue and dark-veined, entire, sometimes notched at the apex. The style apendages are half-ovate, nearly 2 cm. long, violet, and often whitish near the base without, sharply and irregularly serrate. The stigma is two-lobed, the lobes white-margined. The capsule is drooping, ellipsoid or slightly ovoid-ellipsoid, three to four inches long, bright-green, with six broad rounded ridges, thick-matted. The seeds are numerous, in two rows in each capsule-cavity, nearly a half inch broad, irregularly half-orbicular, sometimes very thick, brown, corky- walled.

John K. Small

For more information on historic Irises visit the Historic Iris Preservation Society at

-- BobPries - 2014-12-10
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Topic revision: r1 - 10 Dec 2014, BobPries
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