Eudicots (Tricolpates)

Some General Characteristics


Left photo: A eudicot seedling with two cotyledons. Right photo: A tricolpate pollen grain from a tomato plant (Solanum lycopersicum).

The eudicots are the largest group of flowering plants. Approximately 75 percent of all species of flowering plants belong to this group (Drinnan et al. 1994). The eudicots are so named because their embryos typically have two cotyledons (seed leaves). The prefix "eu-", meaning "true", is used because the eudicots constitute a true or monophyletic group as opposed to the former grouping of "dicot", which is paraphyletic. Although eudicots commonly have two cotyledons, this characteristic does not define the group. Other groups of plants have two (or more) cotyledons, including conifers, cycads, gnetophytes, and some basal angiosperms (Judd and Olmstead, 2004).

In most eudicots, the cotyledons appear above ground. They are the first leaves to emerge, and they usually look different from the true leaves, which appear later. In some eudicots the cotyledons remain underground, so only the true leaves are seen above the soil surface. Plants whose cotyledons appear above ground are said to undergo "epigeal germination", while those with cotyledons remaining below ground are said to undergo "hypogeal germination". In general, epigeal germination is common in early successional plants and in plants with relatively small seeds, while hypogeal germination is common in plants with large seeds, such as oak and walnut (Bazzaz 1979, USFS 1948). However, in some cases, a single genus (containing species with similarly sized seeds) may include some species exhibiting epigeal germination and others exhibiting hypogeal germination. For example, Prunus pensylvanica and P. virginiana have epigeal germination whereas P. americana and P. alleghaniensis have hypogeal germination (Leck et al. 2008, USFS 1948).

Eudicots are sometimes referred to as tricolpates, in reference to their pollen, which has three colpi (furrows or apertures). Tricolpate pollen is unique to eudicots; it is the main characteristic used to distinguish the eudicots from other angiosperms. All eudicots have tricolpate pollen or tricolpate-derived forms.

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Bazzaz, F.A. 1979. The physiological ecology of plant succession. Ann. Rev. Ecol. Syst. 10:351-71.

Drinnan, A. N., P. R. Crane, and S. B. Hoot. 1994. Patterns of floral evolution in the early diversification of non-magnoliid dicotyledons (eudicots). Plant Systematics and Evolution 8(Supplement): 93–122.

Judd, W.S. and R.G. Olmstead, 2004. A survey of tricolpate (eudicot) phylogenetic relationships. American Journal of Botany, 91(10):1627-1644.

Leck, M.A., V.T. Parker, and R.L.Simpson (eds.), 2008. Seedling Ecology and Evolution. Cambridge University Press. New York.

Office of the Federal Register, 2014. Code of Federal Regulations. Title 7 Agriculture. Parts 53 to 209. Revised as of January 1, 2014.Published by the Office of the Federal Register National Archives and Records Administration as a special edition of the Federal Register.

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Soltis, P.S. and D.E. Soltis. 2004. The origin and diversification of angiosperms. Am Journal of Botany. 91(10): 1614-1626.

USFS (U.S. Forest Service) 1948. Woody-Plant Seed Manual. Prepared by the Forest Service. U.S. Department of Agriculture. Miscellaneous Publication No. 654, issued June 1948.

Zomlefer, W.B. 1994. Guide to Flowering Plant Families. The Univeristy of North Carolina Press, Chapel Hill. 430 pages.

Last edited: 29 Jan. 2018