Platanthera flava var. herbiola (R. Br. ex Ait. f.) Luer
Tubercled Rein Orchid
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Habenaria flava var. herbiola, Platanthera flava
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 its range, where only a limited amount of suitable habitat exists.
Platanthera flava var. herbiola (tubercled rein-orchid) was designated a state endangered species in 1984. At that time, only 8 locations had been reported in the state. Since that time, a number of additional locations have been discovered, leading to the conclusion that this species is not as rare as previously thought. For that reason, its status was down-listed to threatened in 2013. Even though more locations have been found, the population trend of P. flava var. herbiola continues downward, as habitats continue to be drained, cleared, and built upon. This is especially damaging in east-central Minnesota, where most of the habitats remain and where pressure is greatest for development. Without careful monitoring and conservation planning, this species could easily slip back into endangered status.
Platanthera flava var. herbiola grows to a height of 17-55 cm (7-22 in.). Leaves number 2-5 per stem, are up to 18 cm (7 in.) long, and 5 cm (2 in.) wide, gradually decreasing in size upward until they grade into the bracts. The inflorescence has 14-53 flowers; each flower is subtended and often exceeded by a pointed bract, 0.8-2.7 cm (0.3-1.1 in.) long. The flowers are greenish or yellowish green; the lip is oblong, 2.7-3.8 mm (1.1-1.5 in.) long, 1.3-3.3 mm (0.5-1.3 in.) wide, with a prominent tubercle rising vertically from near the base of the lip (Smith 2012).
Confirmation of P. flava var. herbiola is simple; in fact, this is a “one-character plant” – just look for the tubercle that gives this orchid its name. It is a small, but very noticeable, knob rising from the top of the lip, just inside the flower. It can be seen on every flower, even withered ones.
The normal habitat of P. flava var. herbiola is moist or wet meadows (wet meadow/carr), or sunny swales in savannas. It also occurs at the margins of shallow marshy lakes, especially where there is a turf of low-growing native grasses or sedges. Some of the habitats resemble small patches of prairie (lowland prairie), though the habitats under discussion are well within the forested region of the state and are perhaps better described as permanent and natural openings in an otherwise wooded (central dry woodland) or savanna landscape. It also seems that habitats tend to be oriented along some transitional edge, rather than in any homogeneous or easily categorized community (Smith 2012).
Soils are generally moist, acidic sand, with a thin layer of organic material or duff on the surface and sometimes a clay layer below the surface. Ground water is usually at, or near the surface. Sunlight is either direct for most of the day or lightly filtered through trees or shrubs; P. flava var. herbiola will slowly disappear if its habitat becomes completely shaded (Smith 2012).
The best habitats for P. flava var. herbiola are to be found on the broad sandy lake plain known as the Anoka Sand Plain, just north of the Twin Cities. Fire and drought were important factors influencing the vegetation of the Sand Plain. Perhaps not surprisingly, dormant-season fires in the spring can result in a flush of P. flava above ground - a response that is very rare among orchids, even prairie orchids (Smith 2012).
With one notable exception, the habitats of this species can be considered high-quality remnants of native habitats that have somehow survived being drained, plowed, or invaded by nonnative plant species, especially Phalaris arundinacea (reed canary grass), and Bromus inermis, (smooth brome). The exception is the drained sediment basins on the iron range in Itasca County, far from its native habitat (Smith 2012).
Biology / Life History
Flowers of P. flava var. herbiola, like the flowers of all orchids, are structurally and behaviorally very complex and have highly specialized relationships with insect pollinators. The specific pollinators of P. flava var. herbiola, however, remain unknown. An orchid fruit is a dry capsule, with several thousand seeds. The seeds are nearly microscopic and disperse on wind currents. Germination of seeds can be difficult; the right combination of factors such as temperature, sunlight, soil moisture, and especially soil fungi are required to trigger the development of orchid seed.
Buds on the underground tuber of P. flava var. herbiola appear to be stimulated to break dormancy by off-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.
There is another peculiarity concerning P. flava var. herbiola, which has not been adequately explained. In general, species of Platanthera (rein orchids) seem to grow scattered about a habitat, usually in low numbers, with perhaps small clusters near an older seed-bearing plant. Platanthera flava var. herbiola, however, is different. It is commonly found growing in dense patches, with as many as 200 stems per square meter. Most of the stems will have no flowers, just leaves, and many will be only a few inches tall. One simple interpretation is that this plant is somehow spreading underground and is sending up shoots from an interconnected system of roots or rhizomes (Sheviak 2002). This would be something truly unique among Platanthera. Although this explanation may contain some truth, carefully excavated clumps have failed to find any underground connection. Each stem is attached to a separate and independent root system, with no evidence of underground spreading. Clearly there is more going on here than meets the eye (Smith 2012).
Conservation / Management
The extensiveloss of prairie and wetland habitat is a serious threat to this species. It is important that every effort be made to protect remaining native prairie and wetland habitats. When considering management of surviving populations, it may be useful to know that the growth of aerial stems and the production of flowers is apparently stimulated by dormant-season spring burns, however, 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 1 or 2 inches above ground, the fire may 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. Other well-documented threats include invasive plant species such as Phalaris arundinacea (reed-canary grass) and excessive increases in woody plant cover. 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.
The best time to search for P. flava var. herbiola is when plants are in flower, from late June through July, and in fruit, from late July through August.
Conservation Efforts in Minnesota
At least two 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.
Author: Welby Smith, MN DNR, 1988
Revised: Welby Smith, MN DNR, 2008 and 2016