Maine Field Office - Ecological Services
Northeast Region

Small Whorled Pogonia (Isotria medeoloides) - Threatened

Small whorled pogonia


Mid-succession mixed upland forests (hardwood to mixed forest)

Known occurrences in Maine: known occurrences from the following counties (towns): Cumberland (Baldwin, Gorham, Harrison, Sebago), Kennebec (Readfield), Oxford (Brownfield, Hiram, Otisfield, Stoneham, Waterford), and York (Acton, Lebanon, Limington, Lyman, Newfield, North Berwick, Parsonsfield, Shapleigh)

Threats: Habitat destruction
Recreational activities


Additional Information


Small whorled pogonia was federally listed as an endangered species in 1982, and reclassified as a threatened species in 1993.

Species Description and Life History

A perennial member of the orchid family, small whorled pogonia produces a smooth, hollow stem from 2 to 14 inches tall and topped by 5 or 6 leaves in a circular arrangement (false whorl). One or two flowers stand in the center of the whorl of leaves. The leaves are milky-green or grayish-green, and the flower is yellowish-green with a greenish-white lip. In the northern part of the species range, plants with flowering buds emerge from the leaf litter in May and bloom in June.

Small whorled pogonia grows in a variety of upland, mid-successional, wooded habitats, usually mixed-deciduous or mixed-deciduous/coniferous forests that are in second or third-growth successional stages. Canopy trees are typically 40 to 75 years old and 8 to 18 inches in diameter. Characteristics of this species’ habitat include a sparse herb and shrub layer, a relatively open understory canopy, thick leaf litter on the forest floor, and gently sloping ground. Soils in which small whorled pogonia grows are generally acidic and dry during most of the growing season. Many sites where this plant occurs are underlain by soils with a hardpan layer that impedes the downward flow of water and leads to the formation of shallow braided channels on the ground surface. Small whorled pogonia is almost always found in proximity to features that create long-persisting breaks in the forest canopy; light availability could be a limiting factor for this species.

Typical canopy species associated with small whorled pogonia include red maple (Acer rubrum), eastern hemlock (Tsuga canadensis), northern red oak (Quercus rubra), white oak (Q. alba), black oak (Q. velutina), scarlet oak (Q. coccinea), white pine (Pinus strobus), American beech (Fagus grandifolia), sweet-gum (Liquidambar styraciflua), and tulip poplar (Liriodendron tulipifera). Typical ground layer species associated with small whorled pogonia include partridge berry (Mitchella repens), Indian cucumber root (Medeola virginiana), New York fern (Thelypteris noveboracensis), sweet lowbush blueberry (Vaccinium pallidum), rattlesnake plantain (Goodyera pubescens), red maple seedlings, oak seedlings, Canada mayflower (Maianthemum canadense), wintergreen (Gaultheria procumbens), starflower (Trientalis borealis), running cedar (Lycopodium digitatum), Virginia creeper (Parthenocissus quinquefolia), cat-brier (Smilax glauca), and Christmas fern (Polystichum acrostichoides).


Habitat destruction is the primary threat to the small whorled pogonia. Residential or commercial development, both directly and indirectly, is a primary factor in the destruction of habitat for this species. Other threats include recreational use of the habitat, herbivory, collection, and inadvertent damage from research activities.


Species Range:

Although sparse, small whorled pogonia is widely distributed, with a primary range extending from southern Maine and New Hampshire through the Atlantic Seaboard states to northern Georgia and southeastern Tennessee. Outlying colonies have been found in the western half of Pennsylvania, Ohio, Michigan, Illinois, and Ontario, Canada.




Last updated: October 2, 2012
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