Platanthera flava var. herbiola (R. Br. ex Ait. f.) Luer
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Platanthera flava, Habenaria flava var. herbiola
Basis for Listing
This unusual orchid is relatively widespread in the northeastern United States and extreme southeastern Canada, and yet it appears to be rare or threatened throughout most of its range. Minnesota lies at the northwestern edge of this range where a limited amount of suitable habitat exists. Up until 1988, there were only 8 reported and 2 confirmed populations of Platanthera flava var. herbiola known to occur in Minnesota. Since that time, over 40 additional populations have been discovered in the state, largely the result of intensive searches by the Minnesota DNR. However, this is not believed to represent an actual net increase in the number of existing populations, just the discovery of previously unknown populations.
Like all orchids, P. flava var. herbiola has 3 sepals and 3 petals, with the lower petal modified into a lip with a slender spur. The shape and form of the lip is diagnostic to the identification of this species. It is oblong, with a base shaped like an arrowhead, and a thick tubercle on the upper surface near the base. The tubercle separates this species from all look-alikes, especially the common P. aquilonis (tall northern bog orchid), which may occur in the same habitat but lacks the tubercle and the arrowhead-shaped base. The variety herbiola of P. flava is distinguished from the typical southern variety by the longer leaf-like bracts on the flowering stalk. A sweet but subtle fragrance of the flowers seems to be sporadic and undetectable by some observers.
Platanthera flava var. herbiola prefers wet prairies and meadows, swales in mesic prairies, or the sandy or peaty habitats along the edges of marshes, swamps, or lakeshores. These habitats are in full sun or in the partial shade of scattered shrubs such as Salix spp. (willows) and Cornus spp. (dogwoods). Only high quality habitats that show little if any impact from human activities seem to be suitable for this orchid. Degraded habitats with a substantial number of non-native species will not support this very rare plant.
Biology / Life History
Flowers of P. flava var. herbiola are structurally and behaviorally very complex and have highly specialized relationships with insect pollinators. Orchid fruits (pods) form in one-chambered capsules with up to several thousand seeds. Orchid seeds are nearly microscopic and spread short distances via wind. Germination can be difficult; the right combination of factors such as rainfall, temperature, soil fungi, sunlight, and moisture are required to trigger the development of an orchid seed. Platanthera flava var. herbiola can also spread by underground stems called rhizomes (Smith 1993). Plants emerge in June, flowers are produced late June through July, and fruits are produced late July through August. Platanthera flava var. herbiola appears to be stimulated to flower by dormant-season fire, but once plants appear above ground they can be severely damaged by fire. This species is also sensitive to drought. Thousands of plants were counted in a St. Cloud population during a wet summer, but only a handful of plants were observed there during the previous two dry summers. It is unknown if the plants actually die during such droughts or if they are able to survive in a state of dormancy.
Conservation / Management
The extensive loss of prairie and wetland habitats is a serious threat to this species. It is important that every effort be made to protect remaining native prairie and wetland communities. When considering management of surviving populations, it is useful to know that the growth of aerial stems and the production of flowers is stimulated by dormant-season spring burns, but the timing of prescribed burns is critical. Burns must occur in early spring before the plants appear above ground. If the burn is conducted when the plants are even just 2.5-5.1 cm (1-2 in.) above ground, the fire can do more harm than good. Livestock grazing is another potential threat. Even moderate grazing can permanently damage these very sensitive habitats. Mowing for wild hay can also be detrimental to the habitat, especially if repeated every year. Poaching has been a long-standing threat to orchids, but so far P. flava var. herbiola has not become popular among orchid fanciers. This situation may change and needs to be monitored.
Conservation Efforts in Minnesota
At least two occupied sites are in public ownership that are being managed in a favorable way for this species. Management includes activities such as dormant-season spring burns, exclusion of motorized vehicles, and maintenance of natural hydrologic conditions.
Buker, W. 1980. Population explosions among the orchids. Castanea 45:144-145.
Kral, R. 1983. A report on some rare, threatened, or endangered forest-related vascular plants of the South. United States Department of Agriculture Technical Publication R8-TP2. 2 Volumes. United States Department of Agriculture Forest Service, Athens, Georgia. x + 1305 pp.
Niemann, D. 1986. The distribution of orchids in Iowa. Proceedings of the Iowa Academy of Science 93(1):24-34.
Smith, W. R. 1993. Orchids of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 172 pp.