Conservation biology of Serapias perez-chiscanoi Acedo in the Guadiana river basis in Extremadura

The rare orchid species Serapias perez-chiscanoi ACEDO is found only in the Guadiana river basin of Extremadura (Spain) and adjacent Portugal. Though some authors have doubts about the taxonomic validity, we consider Serapias perez-chiscanoi as a distinct species because it has a very stable and uniform morphological appearance, a deviant habitat and reproductive behaviour. All plants have pale green flowers and can be divided into two colour variations; the ¿green¿ and the ¿red¿ variation, which mainly involves the venation of all plant parts. Self-pollination takes place when the pollinia disintegrate rapidly onto the stigma, sometimes even before the flowers have opened. Some flowers don¿t open at all, but do produce a fruit (cleistogamy). The leaves of vegetative rosettes are always much longer than the leaves of flowering individuals, probably to ensure their survival by increasing their root system and vegetative biomass before producing the first inflorescence. We visited the ten known locations, but the species had disappeared from five of them during the past 12 years. Fortunately, during subsequent searches of the region, we found six new populations, of which we examined the life stage structure, using three different age states. Only in three populations, juvenile (vegetative) plants occurred, meaning that the majority of the populations show little or no recruitment, which might indicate sub-optimal viability. The habitat can be described as humid pastures, characterized by species of the genera Asphodelus and Scirpus. The soil is slightly acidic with aand very poor in nutrients component. A big difference existed between the average height of plants in different populations, probably related to habitat differences. Serapias perez-chiscanoi has a very high average fruit-set (92%) typical for a selfing species. At the same locations, Serapias lingua had a low average fruit-set of only 10%, typical for a rewardless outcrossing orchid. The Allee-effect does not apply to Serapias perez-chiscanoi. Small populations of Serapias lingua, however, showed a very low fruit-set, intermediately sized populations a high fruit-set and large populations again a low fruit-set. Small but linear populations (along road verges) and plants along the borders of large populations showed high fruit-set percentages. This is probably caused by the fact that naïve insects enter a population at its border and then learn to avoid the rewardless plants as they move inwards. Due to the alarming rate at which Serapias perez-chiscanoi disappears, a species conservation plan needs to be set up urgently to prevent its extinction in the near future