XIV. Platanthera orbiculata (Pursh) Lindl. [syn. Habenaria orbiculata (Pursh) Torr.] (large round-leaved orchid)

Area of Application: Throughout the area covered by the Northwest Forest Plan.

A. Introduction

Platanthera orbiculata is a perennial orchid (Orchidaceae) with a fleshy tuberous root, and a pair of large, succulent, nearly round, basal leaves. Large round-leaved orchid, round-leaved orchid, large round-leaved rein-orchid, and heal-all are common names that have been applied to this species.

Platanthera orbiculata is considered to be closely associated with old-growth habitat, and is classified as a Survey and Manage Strategy 1 and 2 species under the FSEIS/ROD (USDA Forest Service and USDI Bureau of Land Management 1994a, 1994b). This species is on the Washington Natural Heritage Program (1994) Monitor List. P. orbiculata was considered by the Oregon Natural Heritage Program (1998), but was rejected for inclusion on a list because it is not documented to occur in Oregon.

B. Unique Characteristics, Biology, and Ecology

Platanthera orbiculata is characterized by the pair of large, succulent, shiny deep green, nearly round, basal leaves that spread on the ground. Luer (1975) describes the emerging leaves as hugging the ground so closely that they often follow the contour of objects, which cannot be pushed aside as the leaves expand.

This orchid is perennial with a fleshy tuberous root and 2-7 cylindrical roots, a single glabrous flowering stem 20-60 cm tall, with 1-5 lance-shaped bracts. Leaves are usually 2, basal, round and opposite, clasping at the base, glabrous, glossy deep green with silvery underside, somewhat fleshy, 6-16 cm long and 3-14 cm broad. The flowers are pale to deep whitish-green; lip is straight, linear or strap-shaped; spur is long but less than 28 mm, cylindrical, tapering and curved upward at tip; hemipollinarium length is less than 4.6 mm; floral bracts are shorter than the flowers. Flowers are small, 5-25 in a loose, elongated terminal cluster. Fruit is an erect, curved capsule (MacKinnon et al. 1992; Hitchcock et al. 1969; Correll 1950; Williams and Williams 1983).

There are few reports in the literature that specifically address the pollination of Platanthera orbiculata. It is reported to be pollinated by the large moth Sphinx drupiferanum (Pijl and Dodson 1966 in Catling and Catling 1991). The original citation of the night-flying hawk moth (Sphinx drupiferanum) by Sawyer in 1894 may have been in reference to Platanthera orbiculata var. macrophylla rather than var. orbiculata (Luer 1975). Stoutamire (Luer 1975) identified 2 small gray moths, Autographa ampla and Plusia balluca as pollinators of Platanthera orbiculata. There is some question as to which insects pollinate this species, as well as the probability of different species of pollinators over the large geographic range where P. orbiculata occurs.

The flowering period for Platanthera orbiculata is from mid-June through mid-August on the Mt. Baker-Snoqualmie National Forest (Mt. Baker-Snoqualmie Ecology Program files 1995). There appears to be no relationship between date of flowering and elevation.

Orchid seeds have evolved into minute structures with limited food reserves, and rely on an association with a fungus for successful germination and establishment (Arditti et al. 1990). Numerous small seeds are produced and are dispersed primarily by wind. At the onset of germination, orchids go through a heterotrophic phase with their mycorrhizal fungus (Smreciu and Currah 1989). The developing plant relies on nutrition provided by the fungus, such as sugars, minerals, and other growth factors (Smreciu and Currah 1989).

Little is known about the germination requirements of Platanthera orbiculata. Results from germination experiments (Smreciu and Currah 1989), showed that few Platanthera seeds germinated in any of the treatments. Platanthera orbiculata seeds inoculated with Sistotrema sp. had swollen embryos and cracking testa, but no further development. Of the 3 species of Platanthera in the study, Platanthera orbiculata seeds had the poorest germination success and development, and germinated in association with only 1 species of fungus (Smreciu and Currah 1989).

Terrestrial orchids require an association with a fungus for seed germination and plant establishment (Currah et al. 1990). These mycorrhizal associations consist of endophytic fungi that penetrate the cortical cells of the roots. This mycorrhizal association is essential for successful development and competition of orchids in their natural environments (Currah et al. 1990).

Isolates of the endophytic fungi from mycorrhizae of Platanthera orbiculata collected in Alberta were cultured and identified (Currah et al. 1990). They found 2 fungal species, Leptodontidium orchidicola and Sebacina sp., associated with this orchid. Both species are wood decomposing fungi (Lesher and Henderson 1998). Leptodontidium orchidicola is the imperfect stage of the wood decomposing fungus Leptodontium sp. Sebacina sp. was isolated exclusively from the mycorrhizae of P. orbiculata; however, the identification of this fungus is still tentative.

Currah et al. (1990) describe the seasonal development of roots and mycorrhizae of Platanthera orbiculata. This species has a dimorphic root system, with 1 or 2 root-like tubers, and 2 or more fleshy roots, which are replaced annually. This yearly turnover of the root system utilizes considerable energy, which presumably is fueled by the carbohydrates produced by the single pair of leaves, and carbohydrates contributed by the fungus. If the leaves experience browsing, fungal infestation, or other loss of photosynthetic tissue, this may impact the development of the underground structures and may result in decreased viability or vigor of the individual. This aspect of the life history of the species could be one of the limiting factors in the distribution or successful competition of individuals, and perhaps contributes to the vulnerability of this species (Lesher and Henderson 1998).

C. Specific Habitat Associations

Platanthera orbiculata is unusual among rare plants as it is not a species of rare or special habitats. It usually occurs on habitats considered mesic within its geographic range. What limits the species in this region is related to its interactions with other organisms as much as environmental factors. While rare species of rare habitats are particularly vulnerable to the loss of the rare habitat, species such as Platanthera orbiculata are vulnerable to changes in the abundance of other species or subtle shifts in environmental conditions. These other species may include herbivores that consume the plants, old-growth associated fungi on which the species is absolutely dependent for germination and nutrition, or insect pollinators essential for reproduction.

Platanthera orbiculata occurs on sites with moisture regimes that vary from dry to mesic or moist, or even swamps and bogs. Reference is often made to rich or humic forests, mossy sites, and acidic soils (MacKinnon et al. 1992; Hitchcock et al. 1969; Szczawinski 1959; Correll 1950). It occurs primarily at lower to mid elevations. The elevation may range up to 914 m (3000 ft.) in northwest coastal areas and northeastern North America, 1219 m (4000 ft.) in Montana and Idaho, and 1524 m (5000 ft.) in the southeastern United States (Correll 1950).

The only specific habitat information available for western Washington comes from the 47 sightings on Area 1 Ecology plots on the Mt. Baker-Snoqualmie National Forest. More general descriptions available from WNHP data files and herbaria label data generally agree with habitat characteristics documented on ecology plots where Platanthera orbiculata occurs (Lesher and Henderson 1998).

On the Mt. Baker-Snoqualmie National Forest, Platanthera orbiculata occurs primarily in mesic climatic areas (mostly ecozones 8-10, see Henderson et al. 1992), on moderate or mesic sites. It occurs on sites with a mean annual temperature about 8^oC (46^oF) and total annual precipitation about 254 cm (100 in.) (Henderson 1995). It is found at low to mid elevations, on moderate slopes, and on sites which are neither very dry nor very wet. The populations generally spanned an elevation band of about 366 m (1200 ft.). However, the elevation of sample plots ranged from 229-994 m (750-3260 ft.), with an average elevation of 765 m (2510 ft.). This orchid occurs on all aspects, but its distribution shifts slightly with elevation and aspect. It is less common on cooler, northerly aspects where it occurs at lower elevations, up to about 853 m (2800 ft.); on warmer (south and westerly) aspects it is more frequent and occurs over a wider range of elevations, up to 1006 m (3300 ft.).

Bedrock and parent material at Platanthera orbiculata sites is somewhat variable. Schist (36% of plots) was the most common bedrock, followed by gneiss (17%) and granite (15%). Over half the plots occurred on a regolith of neutral colluvium.

Platanthera orbiculata is generally found in mature to old-growth stands. The majority of plots where this orchid occurred were over 130 years old, although the ages of stands ranged from 54 to 837 years. Two-thirds of the plots were in old-growth stands over 200 years old.

Platanthera orbiculata was found most commonly in the mesic to drier plant associations in the Western Hemlock Zone; however 30 percent of the plots occurred in the lower Silver Fir Zone. The most frequent plant associations where Platanthera orbiculata occurred were the mesic types characterized by salal and Oregon grape, e.g., Western Hemlock/Salal-Oregon grape and Western Hemlock/Oregon grape, and the mesic swordfern types, e.g., Western Hemlock/Swordfern-Foamflower and Western Hemlock/Swordfern-Oregon grape plant associations (Henderson et al. 1992). Plots where it occurred in the Silver Fir Zone were often in the moist Alaska Huckleberry types, e.g., Silver Fir/Alaska Huckleberry-Swordfern and Silver Fir/Alaska Huckleberry-Queenscup plant associations (Henderson et al. 1992). Stands were often characterized by coarse woody debris and a deep litter layer. Moss cover was often high; the most common species present were Hylocomium splendens, Rhytidiadelphus loreus, and Rhytidiopsis robusta. Winter snow depth as indicated by the "lichen line" (Henderson et al. 1992) was usually less than 1.2 m (4 ft.).

D. Range of Platanthera orbiculata

1. Known Range

Platanthera orbiculata has a transcontinental distribution with a broad eastern range extending from northeastern Canada, south in the Appalachian Mountains to North Carolina and Tennessee; across the Prairie Provinces in Canada to western North America, where the distribution forms a narrower band (Reddoch and Reddoch 1993), and extends as far south as the central Washington Cascades. A distribution map is provided in Reddoch and Reddoch (1993), but the western distribution of this species is under represented, as it was beyond the scope of their study.

Known locations of Platanthera orbiculata within the region covered by the Record of Decision (USDA Forest Service and USDI Bureau of land Management 1994b) occur only within the State of Washington. Sites under Federal ownership are restricted to the Mt. Baker-Snoqualmie National Forest and North Cascades National Park Complex, including Ross Lake National Recreation Area (Washington Natural Heritage Program files, Mt. Baker-Snoqualmie National Forest Ecology Program and Botany Program files). Platanthera orbiculata is reported from about 70 sites on the Mt. Baker-Snoqualmie National Forest. Of these reports, it is documented on 47 ecology plots that range from Baker Lake south to the Cedar River watershed; 81 percent of these sites occur from Baker Lake south to the Skykomish River. There are a few historical records from herbaria, and the remainder are sites documented in Botany Program surveys. Platanthera orbiculata is not known to occur on the Olympic Peninsula.

The Washington Natural Heritage Program has records for Platanthera orbiculata in Washington State. Of these, 14 sites of Platanthera orbiculata that were documented prior to 1966 may no longer exist due to road building and timber harvest activities over the last several decades. Even more recent sites from the early 1980s may no longer exist. Four sites are documented for the North Cascades National Park Complex, including Ross Lake National Recreation Area. Ten sites are reported for northeastern Washington (Washington Natural Heritage Program files; Lesher and Henderson 1998). Nine of these sites occur on the Colville National Forest and a historical site from 1902 on private land near Calispell Lake. Platanthera orbiculata has been documented from 2 localities on the San Juan Islands, although both populations may no longer exist.

The Oregon Natural Heritage Program (1998) lists Platanthera orbiculata as not documented to occur in Oregon. Peck (1961) does not include P. orbiculata. Gilkey and Dennis (1967) describe Habenaria orbiculata as rare in mountain woods of northern Washington, but do not mention it as occurring in Oregon. The Jepson Manual does not list Platanthera orbiculata as occurring in California (Hickman 1993).

2. Suspected Range

Although the species is not documented for the Olympic Peninsula, it is possible it may occur there.

E. Timing of Surveys

The flowering period for Platanthera orbiculata is from mid-June through mid-August. Surveys can be conducted for Platanthera orbiculata any time during the growing season, generally June through September.

F. Threats

Threats to Platanthera orbiculata are those actions or conditions that may limit or extirpate the species from an area (Lesher and Henderson 1998):

• Indiscriminate spraying to control pest Lepidoptera which could kill the moth pollinators
• Changes in environmental conditions caused by wildfire or timber harvesting activities that may result in heat or drought stress
• Reduction of organic matter by accelerated decomposition (by climate change or timber harvesting activities)
• Introduction of non-native invertebrates (including slugs or snails) which could increase herbivory
• Changes in site conditions which may preclude the occurrence of mycorrhizal fungi
• Changes in climate which could affect the distribution of antagonistic fungi or herbivores.

REFERENCES

Arditti, J., R. Ernst, T. Wing Yam, and C. Glabe. 1990. The contributions of orchid mycorrhizal fungi to seed germination: a speculative review. Lindleyana 5(4): 249-255.

Catling, P. M. and V. R. Catling. 1991. A synopsis of breeding systems and pollination in North American orchids. Lindleyana 6(4):187-210.

Correll, D. S. 1950. Native Orchids of North America North of Mexico. Chronica Botanica Co. Waltham, MA. 399 p.

Currah, R. S., E. A. Smrecui, and S. Hambleton. 1990. Mycorrhizae and mycorrhizal fungi of boreal species of Platanthera and Coeloglossum (Orchidaceae). Can. J. Bot. 68: 1171-1181.

Gilkey, H. M. and L. J. Dennis. 1967. Handbook of Northwestern Plants. Oregon State University Bookstores, Inc., Corvallis, OR. 505 pp.

Henderson, J. A. 1995. Unpublished Potential Natural Vegetation Model. Mt. Baker-Snoqualmie National Forest. Mountlake Terrace, WA.

Henderson, J. A., R. D. Lesher, D. H. Peter and D. C. Shaw. 1992. Field Guide to the Forested Plant Associations of the Mt. Baker-Snoqualmie National Forest. USDA Forest Service, Pacific Northwest Region. R6-ECOL-TP-028-91. 196 pp.

Hickman, J. C. (ed.). 1993. The Jepson Manual: Higher Plants of California. University of California Press, Berkeley, CA. 1400 pp.

Hitchcock, C. L., A. Cronquist and M. Ownbey. 1969. Vascular Plants of the Pacific Northwest. Part 1: Vascular Cryptogams, Gymnosperms, and Monocotyledons. University of Washington Press, Seattle. 914 p.

Lesher, R. D., and J. A. Henderson. 1998. Management Recommendations for Large Round-leaved Orchid Platanthera orbiculata (Pursh) Lindl. [syn. Habenaria orbiculata (Pursh) Torr.]. Unpublished manuscript.

Luer, C. A. 1975. The Native Orchids of the United States and Canada excluding Florida. New York Botanical Garden.

MacKinnon, A., J. Pojar, and R. Coupe' (eds.). 1992. Plants of Northern British Columbia. Lone Pine Publishing, Vancouver, B.C. 351 p.

Mt. Baker-Snoqualmie National Forest Botany Program Database. 1995. Mountlake Terrace, WA

Mt. Baker-Snoqualmie National Forest Ecology Program Database. 1995. Mountlake Terrace, WA

Oregon Natural Heritage Program. 1998. Rare, Threatened and Endangered Species of Oregon. Oregon Natural Heritage Program, Portland, Oregon. 92 pp.

Pijl, L. van der, and C. H. Dodson. 1966. Orchid Flowers, Their Pollination and Evolution. University of Miami Press, Coral Gables. In Catling, P.M. and V. R. Catling. 1991. A synopsis of breeding systems and pollination in North American orchids. Lindleyana 6(4):187-210.

Reddoch, A. H. and J. M. Reddoch. 1993. The species pair Platanthera orbiculata and P. macrophylla (Orchidaceae): Taxonomy, morphology, distributions and habitats. Lindleyana 8(4):171-187.

Smreciu, E. A. and R. S. Currah. 1989. Symbiotic germination of seeds of terrestrial orchids of North America and Europe. Lindleyana 4(1): 6-15.

Szczawinski, A. F. 1959. The Orchids of British Columbia. British Columbia Provincial Museum Handbook No. 16.

USDA Forest Service and USDI Bureau of Land Management. 1994a. Final supplemental environmental impact statement on managing of habitat for late successional and old-growth species within the range of the northern spotted owl. Portland, Oregon.

USDA Forest Service and USDI Bureau of Land Management. 1994b. Final supplemental environmental impact statement on managing of habitat for late successional and old-growth species within the range of the northern spotted owl. Appendix J2, Results of Additional Species Analysis. Portland, Oregon.

Washington Natural Heritage Program. 1994. Endangered, threatened, and sensitive vascular plants of Washington. Department of Natural Resources. Olympia. 52 pp.

Washington Natural Heritage Program. 1995. Sighting reports for Platanthera orbiculata.

Williams, J. G. and A. E. Williams. 1983. Field Guide to Orchids of North America. Universe Books. New York, NY.