The Evolutionary Dynamics of Apomixis in Ferns: A Case Study from Polystichoid Ferns

Figure 2

Diversification of polystichoid ferns through time as inferred using rbcL chloroplast DNA sequences (obtained from GenBank in March 2012) and Bayesian estimates of divergence times using a relaxed molecular clock model. The shown topology is consistent with the results of published phylogenetic analyses of polystichoid ferns, see also David Barrington’s Polystichum website (http://www.uvm.edu/~dbarring/polystichum.htm). The three groups comprising apomictic taxa are indicated as follows: dark color: all or nearly all taxa are reported to be apomictic, middle blue: half or most taxa are reported to be apomictic, and bright blue: minority of apomictic taxa. Thick blue branches: earliest putative origin of apomixis indicated in maximum parsimony reconstructions under the assumption of accelerated gain and putative secondary lost of apomixis. Values above branches indicate probability for ancestral apomixis in the clades depicted as triangles and branches leading to these clades (with <0.01 as the minimum value shown). The grey vertical lines indicate known for enhancement of the monsoon regimes in SE Asia. Abbreviations: CD: Cyrtomidictyum, CY: Cyrtomium, PH: Phanerophlebia, PO1: Polystichum clade 1, and PO2: Polystichum clade 2. C1 includes Cyrtomium species with mainly apomictic reproduction such as C. falcatum, C. fortunei, and C. macrophyllum, whereas C2 includes Cyrtomium known to show sexual reproduction such as C. grossum and C. nephrolepioides, as well as the apomictic C. hemionitis. X1 includes the apomictic taxa Polystichum luctuosum, P. tsus-simense, and P. xiphophyllum, whereas X2 includes the apomictic P. neolobatum and the nonapomictic P. hillebrandii.