Isotria medeoloides

Isotria medeoloides may be distinguished from I. verticillata (Common Whorled Pogonia) by the greenish-white color of the hollow stem and yellow-green flower with a greenish-white tip. Sepal characteristics are also important- sepals linear-lanceolate, 1.2-2.5 cm long, not greatly exceeding the petals (1.3-1.7 cm); peduncles to 2.5 cm, shorter than the ovary. I. medeoloides also resembles young plants of Medeola virginiana (Indian Cucumber-root). I. medeoloides may be distinguished from Medeola by its hollow stout stem; Medeola has a solid more slender stem (USFWS 1996). For a technical description of I. medeoloides see Flora of North America (2002).

Acidic soils of dry to mesic second-growth, deciduous or deciduous-coniferous forests with an open herb layer, although occasionally dense ferns, moderate to light shrub layer, and a relatively open canopy. Soils typically covered with light to moderate leaf litter. Frequently occurs on flats or slope bases near canopy breaks (Flora of North America 2002).

A typical forest community supporting I. medeoloides on fragipan soils in northern New England is dominated by Acer rubrum, Tsuga canadensis, Betula papyrifera, Quercus rubra, Pinus strobus and Fagus grandifolia. Younger stands frequently support Populus grandidentata. A conspicuous indicator of I. medeoloides in this region is abundant Betula papyrifera on slopes with a dense fern understory. Hamamelis virginiana is virtually a constant associate of I. medeoloides here and is usually the dominant shrub species. In southern New England Clethra alnifolia is usually an additional associated shrub.

Herbaceous vegetation at northern I. medeoloides sites varies from virtually none beneath dense Tsuga or Fagus groves to unbroken stands of woodland ferns (mostly Dennstaedtia punctilobula, Athyrium noveboracensis and Osmunda spp.). Medeola virginiana, like Hamamelis, is virtually a constant associate. Woodland sedges and grasses tend to be conspicuously absent, only Brachyeletrum erectum occurring with some regularity. Botrychium matricariaefolium and B. simplex var. tenebrosum are two diminutive ferns which inhabit slightly wetter areas near some I. medeoloides populations - these ferns might, in the preparer's opinion, have some limited value as indicator species. Clubmosses (mostly Lycopodium obscurum and L. complanatum) and evergreen forbs such as Gaultheria procumbens, Epigaea repens, Chimaphila maculata, Mitchella repens, and Pyrola spp. tend to be abundant. Other orchids such as Cypripedium acaule, Goodyera tesselata, G. pubescens, Corallorhiza maculata, C. odontorhiza and Triphora trianthophora frequently occur with I. medeoloides in this region. Brownell (1981) lists an impressive total of eight other orchid species occurring in the vicinity of the Ontario population. In VA, Grimes (1921) listed Malaxis unifolia and Liparis lilifolia as associated orchids, while Ware and Saunders (unpublished report 1983) listed Tipularia discolor and Goodyera sp. as associates.

Although most of the above-mentioned herbaceous species are quite common in a variety of habitats, they can serve as indicators of I. medeoloides when then occur together in abundance. These ferns, clubmosses, evergreen forbs and orchids characterize the plant community found on acidic, sloping, fragipan soils.

Mehrhoff (1980) suggested that declines in I. medeoloides population sizes "are probably related to an increase of vegetative cover at the sites". Recent findings, however, suggest that the amount of vegetative cover I. medeoloides populations has at most minimal influence on the long-term viability of the population. To elaborate, the preparer of this abstract has personally observed hundreds of quite thrifty I. medeoloides plants growing in very dense fern cover. In fact, at some NH populations, one finds the majority of individuals growing in this dense cover. Furthermore, Brumback and Fyler (1983) state, "There seems to no correlation in our study between herbaceous cover and reproductive class.... While it may be true that dense herbaceous cover could certainly limit the size of I. medeoloides, in our study several blooming plants appeared in over 60% herbaceous cover." In cases where smaller less vigorous plants are correlated with dense cover, one cannot assume that competition is the cause. The correlation may simply reflect edaphic conditions which are suboptimal for I. medeoloides but optimal for dense shrub or herb cover.

Nearly all I. medeoloides populations are described as occurring in "second growth" or successional forest communities. This fact alone should not elicit the notion that I. medeoloides therefore requires such relatively young-aged forests. Rather, I. medeoloides is a forest plant and virtually all forests in the region reflect past logging or clearing. Forest maturation does not appear to be a threat to the majority of I. medeoloides population because so many populations already inhabit relatively mature forests.

Nevertheless, the possibility that some I. medeoloides populations are transitory must not be dismissed. The declining MI population inhabiting an abandoned apple orchard (Mehrhoff 1980) may or may not be such a population. In the course of forest community succession and forest soil development, conditions favorable to I. medeoloides may be only temporarily available. Through time, as conditions change, I. medeoloides may decline. At this point in our knowledge, we can only speculate that I. medeoloides is capable of such dynamics.

Because I. medeoloides grows in deciduous as well as evergreen forests, population size is unlikely to be greatly influenced by overstory tree density, basal area, or specific light conditions. Rather, population size, as a variable, seems to depend mostly on the extent and quality of soil habitats.

When openings in the tree canopy allow more light to reach the forest floor and I. medeoloides plants, there is reason to believe that the plant responds favorably, at least in the short term. Brumback (pers. comm. 1985) observed exceptionally vigorous plants adjacent to a recent clear-cut, and smaller, less vigorous plants away from clear-cut. In South Carolina, woods-road edges support I. medeoloides, and extra light might be an important factor (Raynor 1985, pers. comm.). Canopy reduction experiments should be conducted in the future to determine the precise response of I. medeoloides to dramatic increases of light. These findings should have population management implications.

Although soil moisture varies seasonally and can be difficult to measure, I. medeoloides populations tend to occur on soils ranging from dry-mesic to wet-mesic. Drought stress, as reported by Homoya (1977), may periodically occur and cause premature initiation of dormancy. At a NH population, the preparer of this abstract observed extreme stress in an I. medeoloides plant that had its corm nearly totally exposed as result of the erosional effects of water flowing in a migrating intermittent stream channel. Although such damage is probably rare, certain especially heavy rains may take their toll. In the long term, however, the damage done to mature I. medeoloides plants by migrating "braided intermittent streams is probably compensated by the simultaneous creation of new habitats - stream deposited leaf debris - for new I. medeoloides plants.

Researchers at the Smithsonian Environmental Research Center have identified the mycorrhizal fungi associate but their research is not yet published (SERC 2014).

Mehrhoff (1989) determined that the leaf whorl diameter in a given year is a good predictor of the reproductive state for that plant for the following year. Plants that are large one year are likely to bloom the next year, while plants that are small are more likely to be vegetative, go dormant, or die (Mehrhoff, 1989; Vitt, 1991). The small whorled pogonia only occasionally reproduces vegetatively, as indicated by rare occurrences of two or more stems originating from a single root stock (Ames, 1922; Brumback and Flyer, 1983; D. Ware pers. comm., 1992).