Date of this Version
The Prairie Naturalist· 42(1/2): June 2010, pp 55-60
A population of threatened western prairie fringed orchid (Platanthera praeclara) was selected in 2004 on the Sheyenne National Grassland in southeastern North Dakota to study seed production and maturation for future use in population viability modeling. We randomly collected 30 seed capsules from the population under a permit from the U.S. Fish and Wildlife Service to: 1) identify capsule parameters that might be correlated with seed number and viability, 2) estimate an appropriate sample size to obtain accurate seed production estimates, 3) quantify seed production and viability per seed capsule, and 4) document temporal patterns in seed embryo development. We found that the number of seeds per capsule was weakly correlated with capsule weight (R2 = 0.23, P = 0.04), while the proportion of viable seeds within a capsule was weakly correlated with capsule length (R2 = 0.20, P = 0.01) and capsule circumference (R2 = 0.17, P = 0.04). However, seed production and embryo viability varied extensively in our study to the extent that capsule measurements were not reliable indicators of fecundity or fertility. Our study provides guidance for the sample size required to make statistical inferences regarding seed production and seed viability in western prairie fringed orchid populations. Our data also suggest that orchid seeds undergo maturation up to the time of capsule dehiscence based on increases we observed from August to September in seed weights and proportion of large embryos. Our observations reinforce the importance of moratoriums on grazing and mowing in some areas of orchid habitat until after mid-September.