Trillium grandiflorum, the white trillium, large-flowered trillium, great white trillium, white wake-robin or in , is a species of flowering plant in the family Melanthiaceae. A monocotyledonous, herbaceous perennial, the plant is native to eastern North America, from northern Quebec to the southern parts of the United States through the Appalachian Mountains into northernmost Georgia and west to Minnesota. There are also several isolated populations in Nova Scotia, Maine, southern Illinois, and Iowa.
Trillium grandiflorum is most common in rich, mixed upland forests. It is easily recognized by its attractive three-petalled white flowers, opening from late spring to early summer, that rise above a whorl of three leaf-like bracts. It is an example of a spring ephemeral, a plant whose life-cycle is synchronized with that of the deciduous woodland which it favours.
White trillium often occurs in dense drifts of many individuals. The G. Richard Thompson Wildlife Management Area in the Blue Ridge Mountains is renowned for an extensive stand of white trillium that blooms each spring. Over a two square mile area along the Appalachian Trail near Linden, Virginia there is a spectacular annual display of white trilliums estimated at near ten million individuals.
Description Trillium grandiflorum is a perennial that grows from a short rhizome and produces a single, showy white flower atop a whorl of three leaves. Flowering stems are tall. The leaves are often called bracts as the "stem" is then considered a peduncle (the rhizome is the stem proper, aboveground shoots of a rhizome are branches or peduncles); the distinction between bracts (found on pedicels or peduncles) and leaves (borne on stems). 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 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 not as heavily marked as on the leaves. Their overlapping bases and curve give the flowers 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. The flowers are perched on a pedicel (i.e., flower stalk) raising them above the leaf whorl, and grow pinker as they age. The flowers' stigmas are slender, straight or mostly so, narrowing at the end. The white petals are much longer than the green sepals. The flowers have six stamens in two whorls of three, which persist after fruiting. The styles are white and very short compared to the anthers, which are pale yellow, but become a brighter shade when liberating pollen due to the latter's color. The ovaries are six-sided with three 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.
Taxonomy Trillium grandiflorum was first described by André Michaux in 1803 as variety grandiflorum of Trillium rhomboideum, a species now regarded as a synonym of Trillium erectum var. erectum. Michaux described the variety as having broadly rhombic leaves, large white petals, and black fruit. The epithet grandiflorum means "large-flowered", a name that well describes Michaux's variety. In 1805, Richard Anthony Salisbury elevated the variety to a full species. As a consequence, and partially by accident, Trillium grandiflorum is commonly known as the large-flowered white trillium.
, the name Trillium grandiflorum is widely recognized. The species is a member of the Grandiflorum group, a group of species typified by Trillium grandiflorum itself. The group, which also includes Trillium nivale and Trillium ovatum, is sister to a clade comprising subgenus Sessilia (the sessile-flowered trilliums) and subgenus Delostylis (the Catesbaei group).
, Plants of the World Online (POWO) lists 20 synonyms for Trillium grandiflorum. Although POWO accepts no infraspecific names, numerous varieties and forms have been described. Of these, perhaps the best known is Trillium grandiflorum f. roseum , which was described by Oliver Atkins Farwell in 1920. The flower of forma roseum opens a striking salmon-pink instead of the more typical white. The pink color of the form is warmer and more attractive than the pink induced by aging. It occurs rarely throughout the range of the species, except along the Blue Ridge Mountains of Virginia where it is locally frequent. The epithet roseum means "rose-like, rose-colored", and so the form is sometimes called the rose trillium.
Trillium grandiflorum, unlike most trilliums, occasionally produces double-flowered forms with more than three petals. T. grandiflorum f. polymerum , a multipetaled form described by Marie-Victorin Kirouac in 1929, occurs rather frequently in this species. Although these wild forms are stable and healthy, the plants usually lack normal floral organs and are therefore completely sterile. The epithet polymerum means "many-parts", which in this case refers to the many flower petals of the form.
Some variants of Trillium grandiflorum have abnormal green markings on the petals (floral virescence), floral organs that take on a leaf-like appearance (phyllody), or other abnormal characteristics. Many of these forms have been given taxonomic names with epithets such as albomarginatum ("white-margined", referring to the petals), foliaceum, ("leaf-like, leafy"), giganteum ("unusually large or tall"), and longipetiolatum ("with long petioles"). A typical example is the variety Trillium grandiflorum var. variegatum , described by Erwin Frink Smith in 1879. The epithet variegatum ("streaked or spotted with color") refers to its virescent petals, a distinguishing characteristic of this variety. In 1971, it was shown that mycoplasma-like organisms (now called phytoplasmas) were present in all such forms examined (but not in normal plants). The authors concluded that "such plants should now be regarded as diseased T. grandiflorum and the varietal designation of Smith should be considered invalid."
Unlike other species such as Trillium erectum, which hybridize fairly easily, Trillium grandiflorum is not known to form hybrids.
Ecology Trillium grandiflorum favors well-drained, neutral to slightly acid soils, usually in second- or young-growth forests. In the Northern parts of its range it shows an affinity for maple or beech forests, but has also been known to spread into nearby open areas. Depending on geographical factors, it flowers from late April to early June, just after Trillium erectum.Lamoureux, Flore Printanière, p. 48. Like many forest perennials, Trillium grandiflorum is a slow growing plant. Its seeds have double dormancy, meaning they normally take at least two years to fully germinate. The seeds are dispersed in late summer, germinating after a cold and then a warm period, producing a root and after another winter the seedling's cotyledon emerges from the soil. Like most species of Trillium, flowering age is determined largely by the surface of the leaf and size of the rhizome instead of age alone. Because growth is very slow in nature, T. grandiflorum typically requires seven to ten years in optimal conditions to reach flowering size, which corresponds to a minimum of of leaf surface area and of rhizome volume.Lamoureux, Flore Printanière, pp. 429-430. In cultivation, however, wide disparity of flowering ages are observed.
Pollination and seed dispersal Trillium grandiflorum has long been thought to self-pollinate based on the fact that pollinators had rarely been observed visiting the plants and because there is low variation in chromosomal banding patterns. This has been strongly challenged, as other studies have shown high pollination rates by bumblebees and very low success of self-pollination in controlled experiments, implying that they are in fact self-incompatible. Several ovules of a given individual often fail to produce seeds. One contributing factor is pollen limitation, and one study showed that open pollinated plants had 56% of their ovules produce seeds, while in hand pollinated individuals the figure was 66%. Plants with reduced exposure to pollinators were 33% to 50% less likely to produce fruits than those that were, while hand pollinated individuals showed a 100% fruit set (though these fruits did not contain a 100% seed set). Plant resources were shown to be a limiting factor in seed production: when pollen was in abundance, larger plants had a significantly greater seed to ovule ratio than smaller ones. The overall suboptimal seed to ovule ratios suggest that Trillium grandiflorum has evolved to maximize reproductive success in the face of highly stochastic pollination, where some plants may only be visited by a single pollinator in a season.
Trillium grandiflorum has been studied extensively by ecologists due to a number of unique features it possesses. It is a representative example of a plant whose seeds are spread through myrmecochory, or ant-mediated dispersal, which is effective in increasing the plant's ability to outcross, but ineffective in bringing the plant very far. This has led ecologists to question how it and similar plants were able to survive glaciation events during the ice ages. The height of the species has also been shown to be an effective index of how intense foraging by deer is in a particular area.
Fruits are released in the summer, containing about 16 seeds on average. These seeds are most typically dispersed by ants, which is called myrmecochory, but yellow jackets (Vespula vulgaris) and harvestmen (order Opiliones) have both been observed dispersing the seeds at lower frequencies. Insect dispersal is aided by the presence of a conspicuous elaiosome, an oil-rich body attached to the seed, which is high in both lipids and oleic acid. The oleic acid induces corpse-carrying behavior in ants, causing them to bring the seeds to their nesting sites as if they were food. As ants visit several colonies of the plant, they bring genetically variable seeds back to a single location, which after germination results in a new population with relatively high genetic diversity. This has the ultimate effect of increasing biological fitness.
Although myrmecochory is by far the most common dispersal method, white-tailed deer have also been shown to disperse the seeds on rare occasions by ingestion and defecation. While ants only move seeds up to about , deer have been observed to transport the seeds over . This helps to explain post-agricultural colonization of forest sites by Trillium grandiflorum, as well as long distance gene flow which has been detected in other studies. Furthermore, it helps resolve what has been called "Reid's paradox", which states that migration during glaciation events must have been impossible for plants with dispersal rates under several hundred meters (yards) per year, such as Trillium grandiflorum. Thus occasional long distance dispersal events, such as by deer, probably helped save this and other species with otherwise short distance dispersal ability from extinction during the glaciations of the ice ages. Furthermore, nested clade analysis of cpDNA haplotypes has shown that Trillium grandiflorum is likely to have persisted through the last glacial period in two sites of refuge in the southeastern United States and that long distance dispersal was responsible for the post-glacial recolonization of northern areas.