Fig. 3

How cluster-2 Frankia strains spread from Gondwana across the world. (A) Geography from 100 mya, (B) current geography. Geography is according to the plate reconstruction of Zahirovic et al. [49] and paleo-environments from Cao et al. [50]. Land is given in green, deep sea in dark blue, and shallow sea as light blue. For reference, present-day coastlines and geological terrane boundaries are reconstructed using brown lines. Black lines indicate tectonic plate boundaries. Spread of Coriaria with cluster-2 Frankia is indicated by red arrows, hypothetical alternatives are indicated by dashed arrows. Coriaria nodule sampling points referred to in this study are indicated by white triangles. (A) Coriaria spread with the future continental cluster-2 lineage from Gondwana to India (1; continental lineage of Frankia cluster-2), and from Gondwana to South America (2; South American lineage). Distribution from Gondwana to New Zealand and Papua New Guinea (PNG; 3; island lineage of Frankia cluster-2) could have taken place via Australia (3a) or via New Zealand (3b) or in both directions simultaneously. (B) Distribution between PNG and New Zealand is ascertained by the fact that Coriaria is indigenous in all islands of the area [7], but the direction cannot be determined at this point (dashed line). When India had collided with Asia, Coriaria spread in Northern India-Pakistan-Nepal and from there westward to the Mediterranean and eastward into China. The precursor of C. nepalensis spread to the North (dashed arrow, since Coriaria is not found in Northern China today) towards Japan (C. japonica), and from there southward to Taiwan and the Philippines (C. intermedia); the separation of C. japonica and C. intermedia was recent (ca. 10 mya) [7]. The island lineage of Frankia cluster-2 spread from PNG to the Philippines and further to Taiwan (blue arrow), but the original host plants lost the symbiosis or went extinct. Strains of the island lineage outcompeted those of the continental lineage of Frankia when Coriaria spp. spread to Japan and from there to Taiwan and the Philippines. All cluster-2 Frankia strains sampled in continental Eurasia belong to the continental lineage. MD, Madagascar; PH, Philippines; PNG, Papua New Guinea; TW, Taiwan