genus of up to 60 superficially similar species that have a
predominantly central and northern European distribution although
a number of species do reach the Mediterranean and north Africa.
More recently, Coeloglossum viride (Frog Orchid) has been included in this genus.
genus is tricky and presents many problems of identification for even the experienced
field botanist. At the
morphological level the flowers
of most species are relatively similar (D.viridis being the exception), within any species the flowers
show considerable variation in a single population and finally many species
hybridize quite readily. Some help comes at the chromosomal level (see here for more
detailed explanation) where the genus can be divided into two groups, the diploid group (with 40
chromosomes) and the tetraploid group (80 chromosomes).