Dahlia ( or ) is a
genus of bushy,
tuberous,
herbaceous perennial plants native to Mexico. A member of the
Asteraceae (or
Compositae),
dicotyledonous plants, related species include the
sunflower,
daisy,
chrysanthemum, and
zinnia. There are 42
species of dahlia, with
hybrids commonly grown as garden plants. Flower forms are variable, with one head per stem; these can be as small as diameter or up to ("dinner plate"). This great variety results from dahlias being
octoploids—that is, they have eight sets of homologous
chromosomes, whereas most plants have only two. In addition, dahlias also contain many
transposons—genetic pieces that move from place to place upon an
allele—which contributes to their manifesting such great diversity.