This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs with creeping or horizontal, often woody and sometimes tuber-bearing rootstocks, erect stems, erect or ascending equitant leaves, and large regular terminal sometimes pan-icled flowers. Perianth of 6 clawed segments united below into a tube, the 3 outer dilated, spreading or reflexed, the 3 inner narrower, smaller, usually erect, or in some species about as large as the outer. Stamens inserted at the base of the outer perianth-segments; anthers linear or oblong. Ovary 3-celled; divisions of the style petal-like, arching over the stamens, bearing the stigmas immediately under their mostly 2-lobed tips; style-base adnate to the perianth-tube. Capsule oblong or oval, 3-6-angled or lobed, mostly coriaceous. Seeds numerous, vertically compressed, in 1 or 2 rows in each cell. [Greek, rainbow, referring to the variegated flowers.]
About 100 species, mostly in the north temperate zone. Besides the following, some 8 others occur in the southern and western parts of North America. The names Flower-de-luce and Fleur-de-lis are applied to the species, many of which are in cultivation, and highly esteemed for their beautiful flowers. Type species: Iris germanica L.
Stems tall, usually several-flowered, leafy; outer perianth-segments distinctly larger than the inner, native species.
None of the perianth-segments crested; native species.
Leaves 1/2-1' wide.
Leaves somewhat glaucous.
Leaves bright green, not glaucous.
Outer perianth-segments 3'-4' long; flowers sessile.
Outer perianth-segments 2 1/2 -3' long; flowers pedicelled.
Capsule 3-angled; seeds in 1 row in each cavity.
Capsule 6-angled; seeds in 2 rows in each cavity.
Leaves much narrower, 2"-5" wide.
Capsule obtusely angled, 3-6-lobed.
Capsule 3-lobed; northern.
Capsule 6-lobed; western.
Capsule sharply 3-angled.
Outer perianth-segments strongly crested; introduced and widely cultivated species.
Flowers reddish or red-brown; native species.
Flowers bright yellow; introduced species.
Stems low, seldom over 6' tall, 1-3-flowered; outer and inner perianth-segments nearly equal.
Outer perianth-segments crested; leaves lanceolate.
Perianth-tube very slender, exceeding the bracts.
I. crista to.
Perianth-tube expanded above, not exceeding the bracts.
Outer perianth-segments crestless, claws slightly pubescent; leaves narrowly linear.