Eastern prairie fringed-orchid COSEWIC assessment and status report: chapter 8

Biology

Reproduction is through seed (4,500-10,000 seeds/capsule) (Keibler et al. 1993, Stoutamire 1996). For seedlings to become established, mycorrhizae must be present to inoculate the seeds (Bowles 1991). Once established, Platanthera leucophaea reaches reproductive maturity in approximately 3 to 7 years (Keibler et al. 1993). In late summer or early fall, a new bud is produced on a fusiform tuber from which a stem grows during the following year. Growth begins early the next year and plants usually achieve full size by June. The flowering period of P. leucophaea in southwestern Ontario extends from approximately 25 June to 20 July, but this depends on the weather (Brown 1985). If there are very warm days from mid-late June, then flowering can be finished by 5 July. In eastern Ontario, the flowering period extends from about July 4 to July 20 (Reddoch and Reddoch, 1997). Eastern Prairie Fringed-orchid usually produces a spike of 10-40 white flowers (Case 1987). The fruit develops and ripens in late August and early September. Seeds are approximately 1 mm. Additional information on life history, not provided in the original status report, is available in Bowles (1991).

Platanthera leucophaea exhibits adaptations to catastrophic events such as periodic drought and may exist in subterranean, dormant or mycotrophic state for one or more years, but proof that flowering plants revert to subterranean existence is lacking. Vegetative plants, however, have been found in many places where flowering plants previously occurred. The plants are noted for dramatic, mass flowerings following several-year periods of apparent absence. This behaviour appears to be linked to fire-stimulated growth and flowering, although other factors, such as rainfall and soil moisture levels, are likely involved as well (Sheviak and Bowles 1986). Population maintenance is dependent on long-term survival of adults and reproduction by seeds.

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