Genetic and floral divergence among sympatric populations of Gymnadenia conopsea SL (orchideaceae) with different flowering phenology

Gymnadenia conopsea s.l. is a common orchid in central Europe, where early- and late-flowering populations can be distinguished. The early-flowering f orm is recognized as subspecies conopsea and the late-flowering form as sub species densiflora. The two subspecies can occur in sympatry, but their flo wering periods are separated. We investigated whether early- and late-flowe ring subspecies are genetically differentiated, whether they diverged once or repeatedly, and we tried to identify potential evolutionary forces invol ved in the divergence of the two subspecies. We used genetic markers to est imate genetic divergence within and among populations of early- and late-fl owering G. conopsea, and to reconstruct their evolutionary history. In addi tion, we assessed morphological variation between subspecies. Allozyme vari ation indicated that subspecies conopsea was significantly more variable th an ssp. densiflora a and that gene flow among populations of ssp. conopsea was higher than among populations of ssp, densiflora. Gene flow between sub species was low, indicating that the difference in flowering phenology repr esented an effective barrier to gene flow. A neighbor-joining tree based on allozyme frequencies indicated that early- and late- flowering populations did not diverge repeatedly in sympatry. Levels of cpDNA variation were gen erally low, even between G. conopsea s.l. and Gymnadenia odoratissima, chos en as an outgroup. Four cpDNA haplotypes were found, which differed only in the number of microsatellite repeats. Their distribution among subspecies of G. conopsea s.l. and G. odoratissima indicates that microsatellite haplo types have evolved repeatedly, and their occurrence in different taxa thus represents a homoplasy. Floral characters were variable within and among po pulations and subspecies but did not consistently separate early- from late -flowering populations. A weak separation between subspecies was found in v egetative characters that presumably reflected habitat and competitive diff erences experienced by early- and late-flowering populations.