Fortunately, the trilliums as a group are familiar to most people, so that the frequent “sports” that would cause trouble in the keys to family are likely to be recognized as aberrant trilliums. The stigmas of our species are usually described as sessile. They lack a common style, and the stigmatic surface extends along the inner side of each of the 3 separate styles. A number of species native south of Michigan are popular shade garden plants, and these may also eventually be found as escapes.
1. Flower sessile; petals maroon or yellow; leaves usually mottled when fresh.
2. Leaves with distinct (though sometimes short) petioles; sepals becoming strongly reflexed; petals ± abruptly narrowed basally to a slender claw.
2. Leaves sessile; sepals ascending or somewhat spreading; petals convex or gradually narrowed basally, without a slender claw.
3. Petals not over 4 cm long, about twice as long as stamens or shorter; anther connective prolonged ca. 2–4 mm beyond the anther sacs.
3. Petals more than 4 cm long, at least 3 times as long as the stamens; anther connective not or barely (< 0.5 mm) prolonged beyond anther sacs.
4. Flowers maroon, spicy to musky or even fetid-scented.
4. Flowers yellow, lemon-scented.
1. Flower peduncled; petals maroon to white (or green in aberrant or diseased plants); leaves not mottled.
5. Ovary 3-angled to obscurely 3-lobed; leaves definitely petiolate.
6. Plant usually less than 10 cm tall (rarely up to 17 cm), flowering usually in April; leaf blades less than 4 cm long, obtuse or rounded at apex; petals white or sometimes pinkish at base.
6. Plant over 10 (usually over 20) cm tall, flowering in May or June; leaf blades more than 4 cm long, acuminate at apex; petals white, streaked or blotched with purple at base.
5. Ovary strongly 6-angled or -winged and the leaves sessile or subsessile (except in aberrant forms with petioled leaves and/or 3-lobed ovary; these usually also have the petals ± marked with green and are obvious sports).
7. Petals white to pink (never maroon), 3.5–8 (–9.5) cm long, distinctly longer than the sepals, ± obtuse (occasional small plants with shorter petals—though still longer than sepals—may be recognized by the straight styles and broad obovate petals); stigmatic styles straight (though sometimes spreading) or slightly curved at very tip, uniform in diameter; peduncles held above the leaves.
7. Petals white to maroon, usually less than 3.5 cm long (if longer, maroon and/or narrowly acute at apex), seldom much longer than sepals; stigmatic styles spreading, thick at base, tapering, and recurved; peduncles in white-flowered plants (and often also in maroon ones) usually reflexed and held below the leaves.
8. Peduncles erect or slightly bent (rarely nearly horizontal), the flowers held above the leaves; petals and ovary (except in rare yellowish or white forms) deep maroon; petals 2.5–6 (usually 3–4) cm long; filaments usually 1/4–1/2 as long as the anthers (though occasionally longer or shorter); anthers (4.5–) 6–12 mm long.
8. Peduncles bent from the base, usually nearly horizontal or reflexed below the leaves; petals white to maroon, less than 3 cm long (rarely 3.5–4); ovary white or rose; filaments usually less than 1/4 or more than 1/2 as long as the anthers.
9. Filaments about as long as the anthers or occasionally as short as half as long; anthers 3–7 mm long, usually pink when fresh; petals white (rarely rosy), less than 2.5 (rarely 3 or very rarely 3.5) cm long.
9. Filaments very short, almost always less than 2 mm long and less than 1/4 the length of the anthers; anthers 6–15 mm long, yellowish (to pink in maroon-flowered forms); petals white to maroon, (1.5–) 2–3 (–4) cm long.