Evolutionary studies are usually based on dichotomously branching phylogenetic trees. Russell et al. (pp. 37–56) use DNA data from several plastid and low-copy nuclear genes to generate phylogenetic networks of Polystachya, showing reticulate evolution. One group of allotetraploid species has a recent history of long-distance dispersal and multiple hybrid origins; another shows considerable morphological diversity on Madagascar and the Comoros.
A. Russell, R. Samuel, V. Klejna, M. H. J. Barfuss, B. Rupp, M. W. Chase, 2010, 'Reticulate evolution in diploid and tetraploid species of Polystachya (Orchidaceae) as shown by plastid DNA sequences and low-copy nuclear genes', Annals of Botany, vol. 106, no. 1, pp. 37-56 http://dx.doi.org/10.1093/aob/mcq092