The sunflower plant family (Asteraceae) is characterized by head-like inflorescences (capitula) that resemble single solitary flowers but are typically composed of tens to hundreds of flowers that are specialized in structure and function.
Gerbera flower types
In gerbera, three different flower types are distinguished: the marginal ray flowers, the intermediate trans flowers, and the central disc flowers. In each flower type, all basic four whorls of floral organs are found:
- Whorl 1: Flowers of Asteraceae lack conventional green sepals, but in most genera, including gerbera, the base of the corolla is surrounded by hairy pappus bristles, specialized organs that are involved in seed dispersal.
- Whorl 2: Gerbera flowers usually have five petals. Dorsal petals are thin and threadlike in ray and trans florets while lateral and ventral petals are fused together to form a ligule-like structure. This creates the typical bilaterally symmetrical shape of these flowers (zygomorphy). In central disc flowers, petals are shorter and less fused and ultimately, the centermost flower is radially symmetrical (actinomorphic) with separate petals.
- Whorl 3: Although stamen development starts similarly in all types of flowers, the mature ray and trans flowers have only female sex organs. That is because anthers arrest at early stages of development resulting in the formation of nonfunctional staminodes. In disc flowers, anthers develop fully and form a postgenitally fused structure that covers the carpel.
- Whorl 4: Gerbera flowers have one pistil made of two joined carpels. The ovary is inferior located below the floral organs.
History of gerbera
Gerbera species belong to the basal Mutisieae tribe within the large Asteraceae (or Compositae) plant family. The native distribution of this genus, comprising of ca. 30 species, extends to Africa, Madagascar, tropical Asia and South America. The first official description of the South African species Gerbera jamesonii, also known as Transvaal daisy or Barberton daisy, was made by J. D. Hooker in 1889 in Curtis Botanical Magazine. It bears a large capitulum with prominent, yellow, orange, white, pink or various red coloured ray florets. The breeding of gerbera started at the end of the 19th century in Cambridge, England when two South African species, G. jamesonii and G. viridifolia, were crossed by R.I. Lynch. He named the hybrid as Gerbera × cantebrigiensis, known today also as Gerbera hybrida. Today, gerbera is known as an important article of trade and it belongs to the most important ornamental crops in the world together with rose, chrysanthemum, carnation and tulip.