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1927, Iris Prismatica

Addisonia volume 12, page 11, plate 392, 1927


Native of eastern North America.

Family Iridaceae, Iris Family

I. Am. Sept. 30. 1814.
The great antiquity of the slender blue-flag is definitely recorded by its geographic range which includes all three plant-provinces eastward from the highlands, viz. the Blue Ridge, the Piedmont, and the Coastal Plain. The ancestors of this flag preserved in the highland retreats during the submergences of later geologic times sent their descendents through the Piedmont clear to the coast. At the same time it held its own in the Blue Ridge, and today it may be found either in the marshes in the coastal region, or at several thousand feet altitude in the mountains.
This dainty plant is one of the most desirable of our native irises for cultivation. It forms large clumps or extensive colonies; its underground parts, especially the long rootstocks, and slender scaly stems, are firm in texture.
There are no striking characters in the flowers to distinguish them from the flowers of our other blue-flags, but the fruit is characteristic: the half-ripe pod is short and broad with little body and flat wings, but as it matures the body lengthens, becomes relatively narrow, the wings disappear, and a narrow three-angled prismatic capsule is evolved. This opens by three short valves at the summit and allows the numerous seeds to be shaken out as it bobbs about in the wind on the slender stems. The numerous seeds and the virile rootstocks are strong arguments against it having once migrated to other regions than it now occupies and then become extinct there.

In the Coastal Plain the slender blue-flag grows in the turf of bogs .often about cranberry bogs , of the pine barrens . Here its flowers are elevated above the usually depressed associated vegetation. In the mountains, its ancient home, the slender blue-flag occurs in swampy places in the flat valleys which are often submerged by slow-flowing streams during flood periods. Here there is often a peculiar association of northern and southern plants sweet-gale (My rim Gale) and bamboo-vine (Smilax laurifolia) grow side by side. The mountain bog-asphodel (Aiama montana) is associated with the pitcher-plant (Sarracenia rubra), the leather-leaf (Chamaedaphne calyculatd) , the Appalachian cherry (Prunus cuneata) , and two other blue-flags (Iris Carolina and I. versicolor).
The specimens from which the accompanying painting was made were collected at Apple-pie Hill, Burlington County, New Jersey, only a few miles north of Egg Harbor, cited by Pursh as the locality from which the original specimens came. In latitude the species ranges from Georgia to Nova Scotia.
The slender blue-flag has a slender, widely creeping somewhat scaly rootstock. The leaves are erect, "grass-like," two or three together. The blades are very narrowly linear, mostly less than a quarter inch wide, bright green, slenderly attenuate. The flower-stalk is slender, wiry, usually one to two and a half feet tall. The flowers are usually two or three together, arising from a narrow involucre of nearly equal bracts at the top of the stem, long-pedicelled, and often one terminating one or two slender branches. The pedicel is slender, several times as long as the ovary and exceeding the bracts, inequilateral, raising the flower above the bracts. The hypanthium surrounding the ovary is three-sided and sharply three-angled, green. The perianth-tube is short, campanulate, about half as long as the ovary. The three sepals are recurved-spreading, an inch and a quarter to an inch and three quarters long, narrowly pandurate. The blade is broadly rounded, with a white background, yellow-tinged at the base and veined and flecked with blue which merges about the edges. The claw is broad, longer than the blade, magenta-striped at the base, yellowish green at the middle with a rib but no crest, whiter on the edges and with purple veins. The three petals are spatulate, about one and a half inches long, often nearly as long as the sepals, the narrow inrolled claw veined with magenta, the longer blade pale blue with deeper-colored veins. The three stamens are fully three quarters of an inch long, with a filament and anther about equal in length, the filament, and usually the anther, also magenta-tinged. The style-branches are usually less than an inch long, linear-cuneate, magenta, deeper-colored within. The style-appendages are obliquely ovate, about a quarter of an inch long, angular-toothed. The stigma is entire, sparingly erose at the tip. The capsule is narrowly prismatic-cylindric, one to two inches long, rather sharply three-angled, thin-walled, shorter than the slender pedicels, three- valved at the apex. The seeds, in one row in each capsule-cavity, are circular, or through mutual pressure sometimes half-circular, about one sixth of an inch in diameter, brown, scarcely corky, somewhat shining.
John K. Small.

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

-- BobPries - 2014-12-09
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Topic revision: r3 - 11 Dec 2018, BobPries
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