Strawberries are not true berries. The fleshy and edible part of the fruit is a receptacle, and the parts that are sometimes mistakenly called "seeds" are achenes.
There are more than 20 different Fragaria species worldwide. Numbers of other species have been proposed, some of which are now recognized as subspecies.Key to the classification of strawberry species is recognizing that they vary in the number of chromosomes. There are seven basic types of chromosomes that they all have in common. However, they exhibit different polyploidy. Some species are diploid, having two sets of the seven chromosomes (14 chromosomes total). Others are tetraploid (four sets, 28 chromosomes total), hexaploid (six sets, 42 chromosomes total), octoploid (eight sets, 56 chromosomes total), or decaploid (ten sets, 70 chromosomes total).
As a rough rule (with exceptions), strawberry species with more chromosomes tend to be more robust and produce larger plants with larger berries.