- The Genus Fragaria (Rosaceae)
The Fragaria species have been classically defined on the basis of morphological features, ploidy, cross-fertility, and geographic distribution.
The genus is comprised of at least 21 species, including some newly characterized Asian species.
Four levels of ploidy are represented among the recognized species:
- diploid (2n=2x=14)
- tetraploid (2n=4x=28)
- hexaploid (2n=6x=42)
- octoploid (2n=8x=56)
Many interspecific hybrids have been
described, among which triploids (3x), pentaploids (5x), and various other "odd-ploids" are represented. The potential for interspecific hybridization
in Fragaria, even across ploidy levels, suggests that gene introgression may be a complicating factor for molecular phylogenetics, and emphasizes
the need for a phylogenetic analysis of the genus that is based upon multiple, independently segregating loci.
- Geographic Distribution of Wild Fragaria Species
The Fragaria species distribution falls roughly into three zones: the Americas, Europe/Northern Asia, and Asia proper. Potential clues to the diploid
ancestries of hexaploid F. moschata and the various tetraploids are evident from patterns of geographic range sharing. However, the
geographic disjunction between the octoploids and their potential diploid ancestors (other than the broadly distributed F. vesca) leaves
the phylogenetic and biogeographical history of the octoploids open to speculation.
Map of Global Strawberry Distribution
- Origin of the Cultivated Strawberry
Historically, several Fragaria species and novel hybrids have been brought into cultivation in various parts of the world, including F. chiloensis
(8x) in South America, F. moschata (6x) and F. vesca (2x) in Europe, and others. However, the current economic significance of all other
Fragaria species combined is insignificant compared to that of F. × ananassa. Therefore, use of the term "cultivated strawberry" in
this website will refer specifically to F. × ananassa, unless otherwise stated.
The hybrid origin of F. × ananassa traces to Europe in the 1700's. Representatives of the octoploids F. chiloensis and F. virginiana
that had previously been brought from South and North America, respectively, were evidently grown in proximity to each other in European horticultural gardens.
Cross-pollination produced hybrids that were quickly recognized for their unique combinations of morphological and fruit characteristics, and were
brought into cultivation and breeding. Thus, the immediate progenitors of F. × ananassa are the American octoploids, F. chiloensis
and F. virginiana. The latter two species may have arisen from a common octoploid ancestor; however, no lineage has been established connecting
the octoploids to any lower ploidy level. Notably, the only hexaploid Fragaria species, F. moschata, has been considered a highly unlikely
contributor to the octoploids' ancestry on the basis of factors such as its morphological distinctness and geographic separation.