Trillium grandiflorum is a perennial that grows from a short rhizome and produces a single, showy white flower atop a whorl of three leaves. These leaves are ovate (i.e., egg-shaped) in outline with pointed tips. They lack petioles (or have extremely short ones) and measure 12–20 cm long by 8–15 cm wide (5-8 in long by 3–6 in width), with very prominently engraved venation. The leaves and the stem share a dark green color and persist into autumn. Leaves and petals both have somewhat undulate margins, the leaves often much more strongly so. Individuals grow to between about 15 and 30 cm tall (6–12 inches). A single rootstock will often form clonal colonies, which can become very large and dense.
The erect, odorless flowers are large, especially compared to other species of Trillium, with 4 to 7 cm (1.5 to 2.7 in) long petals, depending on age and vigor. The petals are shaped much like the leaves and curve outward. They have a visible venation, though this is nowhere near as marked as on the leaves. Their overlapping bases and curve give the flower a distinctive funnel shape. Between the veined petals, three acuminate (ending with a long point) sepals are visible; they are usually a paler shade of green than the leaves, and are sometimes streaked with maroon. Flowers are perched on a pedicel (i.e., flower stalk) raising them above the leaf whorl, and grow pinker as they age.
Flowers have six stamens in two whorls of three, which persist after fruiting. The styles are white and very short compared to the 9–27 mm (0.5–1 in) anthers, which are pale yellow but becomes a brighter shade when liberating pollen due to the latter’s color. The ovary is six-sided with 3 greenish-white stigmas that are at first weakly attached, but fuse higher up. The fruit is a green, mealy and moist orb, and is vaguely six-sided like the ovary.—Wikipedia