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..
Trillium sessile L. Sp. PI. 340. 1753.
Stem 4'-12' tall. Leaves ovate, oval or nearly orbicular, sessile, acute or obtuse and cuspidate at the apex, 1 1/2'-6' long, often blotched; flower sessile, erect; sepals lanceolate, acute or obtuse, spreading, i'-2' long, petals lanceolate, acute or obtuse, somewhat longer than the sepals, erect-spreading, purple or green; anthers 3"-7" long, longer than filament, the connective prolonged beyond the sacs; berry globose, 6-angled, about 1/2' in diameter.
Trillium viride Beck, Am. Journ. Sci. 11: 178. 1826.
Perennial by a short corm-like rootstock, light green. Stems solitary, or several together, 4'-15' .tall, rough-pubescent near the top, or glabrous in age; leaves oblong to ovate, 2'-4' long, obtuse or acutish, 3-5-nerved, usually blotched, more or less pubescent on the nerves beneath; flowers sessile; sepals linear or linear-lanceolate, l'-2' long, bright green, acute or obtuse; petals clawed, the blades linear or nearly so, surpassing the sepals, light green or purplish green, the claws sometimes brown or purple; stamens about 1/3 as long as the petals; filaments flattened, 1/4-1/5 shorter than the anthers.
In woods and glades, Kansas to Missouri, Tennessee, Mississippi and Arkansas. Spring.
Trillium recurvatum Beck, Am. Journ. Sci. 11: 178. 1826.
Stem 6-18' tall. Leaves ovate, oval or oblong, 1 1/2'-4' long, acute at the apex, narrowed into petioles 3"-9/' long, sometimes blotched; flower sessile, erect; sepals lanceolate, acuminate, 6"-15" long, reflexed between the petioles; petals spatulate or oblong, nearly erect, clawed, acute or acuminate, equalling the sepals or somewhat longer; anthers 4"-7" long, much longer than the filaments, the connective prolonged beyond the sacs; berry ovoid, 6-winged above, about 9" long.
In woods and thickets, Ohio to Minnesota, Mississippi and Arkansas. April-June.
Trillium nivale Riddell, Syn. Fl. W. States, 93. 1835.
Stem 2'-6' high. Leaves ovate, oval or nearly orbicular, 1'-2' long, obtuse at the apex, rounded or narrowed at the base, petioled; petioles, 2"-6" long; flowers peduncled; peduncle 1/2'-l' long, erect, bent, or recurved beneath the leaves; sepals narrowly oblong or oblong-lanceolate, obtuse, 1/2'-1" long; petals white, oblong or oval, obtuse, longer than the sepals, erect-spreading; anthers about as long as the filaments, the connective not prolonged beyond the sacs; styles slender; berry globose, 3-lobed, about 1/2' in diameter.
In woods and thickets, Pennsylvania to Ohio and Minnesota, south to Kentucky and Nebraska. Showy or Dwarf white wake-robin. March-May.