Flora of the Southeastern United States
2022 Edition

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Key A: trilliums with sessile flowers and mottled leaves (subgenus Sessilium)

1 Plants prostrate, with scapes very short, holding bracts (leaves) near the ground; floral fragrance of rotting meat or manure-scented
..2 Anther dehiscence extrorse; bract apices rounded or obtuse, typically mottled only in 2 colors, silver and green
..2 Anther dehiscence introrse; bract apices obtuse or acute, conspicuously mottled in silver and three or more shades of green
....3 Rhizome 0.3-1 cm in diameter, branching, forming clonal patches; scape straight, ascending, densely puberulent on angles; bract blades typically < 6 cm long; petals 1.5–3 cm in length, widest at middle; floral fragrance of horse manure
....3 Rhizome 0.8-1.5 cm in diameter, unbranched, not forming clonal patches; scape S-shaped, decumbent or semi-decumbent, glabrous; bract blades typically > 7 cm long; petals (2.2–) 3.0–5.0 (–6.0) cm in length, widest above the middle; floral fragrance of rotten meat
1 Plants erect or ascending, with tall scapes holding bracts (leaves) well above ground, or sometimes bract tips barely touching the ground in early anthesis; floral fragrance various, foetid, pleasant, or mildly unpleasant
......4 Sepals abruptly deflexed between and below the leaves, distinctly descending below the approximately horizontal plane of the leaves; filaments about as long as incurved anthers; [T. recurvatum group].
........5 Anther connectives slightly incurved or erect; filaments short (< ½ the anther length); [variously endemic to either Kershaw and Richland counties in the inner Coastal Plain of SC or Hamblen and Hawkins counties in the Ridge and Valley of TN].
..........6 Ovary 6-16 mm long; filaments less than ½ as long as the ovary; stigma lobes ca. 1× as long as the ovary, the stigmatic surfaces smooth; [endemic to Kershaw and Richland counties in the inner Coastal Plain of SC]
..........6 Ovary 2-4 mm long; filaments about equal to the ovary; stigma lobes ca. 2× as long as the ovary, the stigmatic surfaces strongly crested-undulate; [endemic to Hamblen and Hawkins counties in the Ridge and Valley of TN]
........5 Anther connectives strongly incurved; filaments long, > ½ the anther length; [primarily west of the Blue Ridge and south into the Gulf Coastal Plain, very rarely disjunct to the Mountains or upper Piedmont].
............ 7 Leaves sessile or subsessile, borne in a descending or drooping manner (similar to the sepals); petals usually 4-7× as long as wide, strongly clawed
............ 7 Leaves distinctly petiolate, borne in an ascending manner (strongly contrasting in position with the strongly deflexed sepals); petals usually ca. 2× as long as wide, attenuate to weakly clawed
......4 Sepals erect, ascending, or spreading, usually borne at or above the approximately horizontal plane of the leaves; filaments much shorter than the upright anthers.
............ ..8 Petals spreading to horizontal, with 1-2 spiral twists (looking something like an airplane propeller); anther dehiscence extrorse (toward the outside of the flower); [T. sessile group]
............ ..8 Petals erect to slightly spreading, not spirally twisted; anther dehiscence introrse (toward the inside of the flower), or latrorse (toward the side).
............ ....9 Petals broadly spatulate, clawed, broadly rounded (though sometimes with an apiculus) at the tip; petals pale lemon-yellow (the claws greenish or maroon); flower fragrance clove-like; [of the Savannah River drainage, from sw. NC southeastward along the GA-SC border]; [T. sessile group]
............ ....9 Petals lanceolate, elliptic, obovate, or oblanceolate, but not broadly spatulate and distinctly clawed, generally acute at the tip; petals maroon-red, purplish-brown, yellow, or green; flower fragrance various; [collectively widespread in our area].
............ ......10 Stigmas > 1.5× as long as the ovary; stamens about 0.5× as long as the petals; anther connectives prominently prolonged into a beak 1.0-5.0 mm long (beyond the anther sacs); [T. sessile group]
............ ......10 Stigmas as long as the ovary or shorter; stamens < 0.5× as long as the petals; anthers blunt, the connectives extended < 1.0 mm beyond the anther sacs.
............ ........11 Ovary ellipsoid; leaves acute, the margins of the outer 1/3 more or less straight; leaf blade mottled with 3 or more shades of green, the palest shade forming a very conspicuous pale silvery-green streak along the midvein; [of the Coastal Plain and fall-line area of GA, AL, and FL Panhandle]; [T. sessile group].
............ ..........12 Stem 2.5-3× as long as the leaves; petals oblanceolate-obovate, usually 1.5-3× as long as wide; flower fragrance yeasty-sweet (or similar to overripe bananas)
............ ..........12 Stem 1-2× as long as the leaves (though sometimes elongating late in the season); petals narrowly elliptic to oblanceolate-obovate, usually 3-5× as long as wide; flower fragrance yeasty-sweet (or reminiscent of stale beer)
............ ........11 Ovary ovoid; leaves acute to acuminate, the margins of the outer 1/3 convex; leaf blade mottled with 2-3 shades of green, paler shades sometimes prominent along the midvein, but not as above; [collectively widespread in our area]; [T. maculatum group].
............ ............ 13 Petals < 4× as long as wide, elliptic-oblanceolate to oblanceolate; [of inland provinces, rarely in the Coastal Plain].
............ ............ ..14 Flower fragrance fruity-spicy, like green apples or Calycanthus (rarely musky); petals maroon, bronze, green, yellow; portions of ovary and stamens purplish during anthesis
............ ............ ..14 Flower fragrance lemon-like; petals greenish-yellow darkening to yellow; ovary and stamens greenish-white during anthesis
............ ............ 13 Petals > 4.5× as long as wide, narrowly oblanceolate-spatulate to linear-oblanceolate; [of the Coastal Plain, rarely farther inland].
............ ............ ....15 [of TX, OK, AR, MO, KS, and IL]
............ ............ ......16 Leaf apices blunt to rounded; leaf upper surface with numerous stomates across the surface (visible as white dots with 10× magnification); stamens ca. 1.5× as long as the ovary
............ ............ ......16 Leaf apices acute; leaf upper surface lacking stomates (or present only near apex); stamens ca. 2× as long as the ovary
............ ............ ....15 [of TX, LA, MS, AL, GA, SC, and FL]
............ ............ ........17 Ovary 3-angled at base of stigmas (rarely 6-angled); petals 7-17 mm wide, narrowly spatulate (appearing clawed); outer whorl of stamens broader, anther dehiscence introrse; flower fragrance faintly spicy-fragrant, banana-like; [of AL, n. FL, GA, and e. SC]
............ ............ ........17 Ovary 6-angled; petals 3-8 mm wide, linear-oblanceolate, narrowly elliptic, to linear-lanceolate (weakly or not clawed); flower fragrance putrid, like rotting meat; [of MS, LA, and e. TX].
............ ............ ..........18 Stamens ca. 2× as tall as the ovary; [of w. LA and e. TX]
............ ............ ..........18 Stamens <1.5× as tall as the ovary; [of c. and e. LA and w. MS].
............ ............ ............ 19 Petals 3-5 mm wide; anther dehiscence introrse; anther connective extending 1-1.5 mm beyond the anther sacs
............ ............ ............ 19 Petals 4-8 mm wide; anther dehiscence latrorse; anther connective scarcely extending beyond the anther sacs