Strawberries. James F Hancock
F. virginiana and F. chiloensis has been observed in cluster analysis of morphological characters, simple sequence repeats and RAPDs (Fig. 1.9; Harrison et al., 1997b; Hokanson et al., 2006). Yang and Davis in their phylogenetic study also found substantial divergence, finding a number of well-supported clades comprised of sequences exclusively from F. chiloensis and F. virginiana.
The origin of Hawaiian and Chilean F. chiloensis is also obscure, but presumably they were introduced from North America via bird migrations. Dillenberger et al. (2018) found F. chiloensis from Oregon and Northern California to be sisters to a Chilean sample of F. chiloensis, but only a handful of F. chiloensis clones were analysed. It is likely that multiple introductions were made into Chile as the habitats of South American F. chiloensis have an extensive range from beaches and headlands to montane forests at 1900 m elevation (Darrow, 1966; Cameron et al., 1991, 1993). Glaucous forms of octoploids may also have been introduced, as at high elevations in Chile leaf colour and thickness resemble F. virginiana ssp. glauca (Cameron et al., 1993).
Origin of decaploid species
Because of the current sympatry between the octoploid F. virginiana ssp. platypetala, diploid F. vesca ssp. bracteata and the decaploid F. cascadensis in the Cascade Mountains of Oregon, it was originally hypothesized that F. cascadensis originated from hybrid polyploid speciation between the two octoploid and diploid congeners (Hummer, 2012). However, Wei et al. (2017a) discovered its origin was more likely due to an ancient hybrid speciation in Beringia. In a phylogenetic analysis of linkage-mapped chromosomes from targeted sequences, they found that the additional subgenome of F. cascadensis was derived from a F. iinumae-like diploid progenitor rather than F. vesca ssp. bracteata. The F. cascadensis found in the Oregon Cascade Mountains may be a remnant of a more widespread species that survived in a Willamette Valley refugium during the last glacial maximum (Dillenberger, 2018). Whether F. cascadensis and the other decaploid F. iturupensis have a common ancestor or evolved independently is unknown. They could have both evolved in Beringia and then moved southwards in different directions along the Pacific Ocean and became isolated (Wei et al., 2017a).
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