tapetums

Tapetums, in biology, refers to distinct tissues that share a common name but occur in different organs and contexts. The term derives from the Latin tapetum, meaning a carpet or covering, a reference to the layered, often reflective appearance of these tissues. The plural form is used when discussing multiple tissues of this type across organisms or contexts.

In zoology, the tapetum lucidum is a reflective layer behind the retina that enhances night vision by bouncing light back through the photoreceptor layer. This increases a viewer’s sensitivity to low light and contributes to eyeshine observed when light is shone into the eye at night. There are two principal structural variants: the cellular (tapetum lucidum cellulosum), which contains reflective crystals, and the fibrous (tapetum lucidum fibrosum), composed of fibrous tissue. The presence and type of tapetum vary among species; many nocturnal mammals possess it, while humans and some primates lack a functional tapetum.

In botany, the tapetum is the nutritive tissue of the anther wall, forming the innermost layer that nourishes developing pollen grains. This tissue can be classified by developmental origin into two main types: plasmodial (syncytial) tapetum, where cytoplasm from several cells forms a multinucleate mass, and glandular (secretory) tapetum, where individual tapetal cells persist and secrete nutrients. The tapetum plays a crucial role in pollen maturation and contributes to pollen wall formation in many species.

Overall, tapetums describe specialized tissues serving light reflection in eyes or nutrient support in pollen development, depending on the biological context.