A theca (plural thecae) refers to any case, covering, or sheath.
In botany, the theca of an angiosperm is half of the anther. An anther and its filament form together a typical (or filantherous) stamen, part of the male floral organ.
Each anther is bilocular, i.e. it consists of two thecae. Each theca contains two pollen sacs (the male sporangium with the microspores).
The tissue between the locules and the cells is called the connective and the parenchyma. Both pollen sacs are separated by the stomium. When the anther is dehiscing, it opens at the stomium.
The outer cells of the theca form the epidermis. Below the epidermis, the somatic cells form the tapetum. These support the development of microspores into mature pollen grains. However, little is known about the underlying genetic mechanisms, which play a role in male sporo- and gametogenesis.
The thecal arrangement of a typical stamen can be as follows :
- divergent : both thecae in line, and forming an acute angle with the filament
- transverse (or explanate) : both thecae exactly in line, at right angles with the filament
- oblique: the thecae fixed to each other in an oblique way
- parallel : the thecae fixed to each other in a parallel way
In biology, the theca of follicle can also refer to the site of androgen production in females.