Trillium grandiflorum (common names white trillium, large-flowered trillium, great white trillium, white wake-robin, French trille blanc) is a species of flowering plant in the family Melanthiaceae. A monocotyledonous, herbaceous perennial, it 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. It also thrives on Vancouver Island in British Columbia. There are also several isolated populations, such as in Nova Scotia and Iowa.
Trillium grandiflorum is most common in rich, mixed upland forests. It is easily recognised by its attractive three-petaled 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 synchronised with that of the deciduous woodland which it favours.
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 10 meters, deer have been observed to transport the seeds over 1 kilometer. 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 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.
In addition to the lateral dispersion (by invertebrates and deer) there is also importance in the fact that burial (vertical dispersion) by ants (or other vectors) increases the survival of new plants by two mechanisms. First, vertical dispersion ensures sufficient depth to preserve the seeds through their dormancy (Trillium seeds are normally dormant for their first year). Second, vertical dispersion ensures adequate anchorage of the rhizomes. This is particularly important for young plants because their small rhizomes, with few & short roots, are easily dislodged (e.g. frost heaveal and other erosion factors) and desiccated.
Interaction with deer
Trillium grandiflorum as well as other trilliums are a favored food of white-tailed deer. Indeed, if trilliums are available deer will seek these plants, with a preference for T. grandiflorum, to the exclusion of others. In the course of normal browsing, deer consume larger individuals, leaving shorter ones behind. This information can be used to assess deer density and its effect on understory growth in general.
When foraging intensity increases, individuals become shorter each growing season due to the reduction in energy reserves from less photosynthetic production. One study determined that the ideal deer density in northeastern Illinois, based on T. grandiflorum as an indicator of overall understory health, is 4 to 6 animals per square kilometer. This is based on a 12 to 14 cm stem height as an acceptable healthy height. In practice, deer densities as high as 30 deer per square kilometers are known to occur in restricted or fractured habitat where natural control mechanisms (that is, predators like wolves) are lacking. Such densities, if maintained over more than a few years, can be very damaging to the understory and lead to extinction of some local understory plant populations.
Trillium grandiflorum is one of the most popular trilliums in cultivation, primarily because of the size of its flowers and its relative ease of cultivation. Although not particularly demanding, its cultivation is a slow and rather uncertain process, due to usually slow growth, wide variations in growth speed and sometimes capricious germination rates. As a result, the vast majority of plants and rhizomes in commerce are collected in the wild, and such heavy collecting, combined with other pressures such as habitat destruction and grazing, may effectively endanger the plants in some areas. This also creates tensions between Trillium enthusiasts and conservation proponents. Transplantation (as with almost all non-weedy wild plants) is a delicate process, and in many cases results in the death of the plant. In cultivation, T. grandiflorum may flower in as little as 4 to 5 years after germination (compared to the usual 7 to 10 in the wild), but these cases appear to be exceptions rather than the rule. One study revealed 20 or so individuals performing so well out of about 10,000 seeds planted, only 20% of which germinated after a year. However, barring plant destruction, T. grandiflorum can continue flowering every year after it has begun.
As a particularly conspicuous forest flower, T. grandiflorum was designated the provincial emblem of Ontario in 1937 (Flora Emblem Act), and as the state wild flower of Ohio in 1987. As a symbol of Ontario, a stylized trillium flower features prominently on the official flag of the province's French-speaking community. It is also frequently used by the Canadian Heraldic Authority to represent Ontario in grants of arms. Although a network of laws make picking wildflowers illegal in the province on any Crown or provincially owned land, it is not, unlike widely believed, specifically illegal (or necessarily harmful) to pick the species in Ontario.
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- For examples see here[permanent dead link] or here[permanent dead link].
- Media related to Trillium grandiflorum (category) at Wikimedia Commons
- Data related to Trillium grandiflorum at Wikispecies
- Biodiversity Information Serving Our Nation (BISON) occurrence data and maps for Trillium grandiflorum