In 2006, I first observed a white-flowered Orchis militaris in a grassland area near Frankfurt. It re-appeared in five following years. Last time I have seen it in 2010. But then it disappeared, no sign of an albiflora form among the more than 100 Orchis militaris plants of these meadows. Until this year, when it flowered again in a distance of about five meters from the first plant.
After the first third of May the inflorescence was already about to fade. The orchid expert Werner Hahn told me that in the 1980s the flowering in this habitat started only at about mid May – clearly a consequence of climate change in the last more than 30 years.
But the question remains: What is the reason that the albiflora form has a comeback after ten years? Seeds of the white-flowered plant might have been spread on this meadow. The color of flowers is a factor which is inherited by dominant alleles. But there still remains the small chance that the genetic characteristics of white flower will be expressed by the new plant in a population of more than 100 plants of the standard color.
The probability of albiflora forms among populations of Orchis militaris is about 1/1000, I guess. In the Middle Rhine Valley this beautiful plant is just flowering:
