thalline

Thalline is an adjective used in biology to describe tissues or organisms that are thallus-like, meaning they have a simple, undifferentiated vegetative body rather than the more complex organs found in many higher plants. The term is often applied to organisms whose main vegetative structure is a thallus—a sheet- or filament-form body capable of photosynthesis and growth.

Etymology: The word derives from the Latin thallus, itself from the Greek thallos, meaning a green shoot or twig. In scientific usage, thalline emphasizes the body’s resemblance to or composition of a thallus.

In lichens, thalline refers to the vegetative thallus that forms the visible body of the organism. This thallus can bear reproductive structures such as apothecia, and its appearance and texture help distinguish lichen forms (for example, crustose, foliose) from other growth forms. The term is used descriptively to contrast the thallus with specialized tissues or reproductive units.

In bryophytes and related groups, thalline (or thalloid) describes plants with a flat, undifferentiated thallus rather than a segmented, leafy morphology. Liverworts provide a common example, with thallose (thalloid) species possessing a continuous thallus, while leafy liverworts have a more differentiated, leaf-like structure.

Other uses: In mycology and phycology, thalline describes tissues derived from or resembling the thallus. The term is primarily descriptive and used to characterize morphology rather than to define taxonomic relationships.

See also: thallus.