Thallosammalet

Thallosammalet is a term used in bryology to describe bryophyte individuals whose main vegetative body is a thallus—a flat, often undifferentiated, photosynthetic tissue. The term is commonly employed in Swedish botanical literature to distinguish thalloid bryophytes from leafy bryophytes, where the plant body shows clear stem- and leaf-like structures.

Morphology and growth form

A thallus is typically dorsiventrally organized and may be simple or lobed. It lacks true vascular tissues and persistent stems or leaves. The thallus is anchored to its substrate by rhizoids and functions as the primary photosynthetic organ of the plant. In liverworts, thalli can be smooth or ribbed and may produce reproductive structures in discrete features on the surface. In hornworts, the thallus is usually simple and irregular, contributing to the plant’s overall thalloid appearance.

Lifestyle and reproduction

Thallosammalet bryophytes are usually small and inhabit moist environments where photosynthesis can occur efficiently. They reproduce asexually through structures such as gemma cups in some liverworts, producing propagules that disperse vegetatively. Sexual reproduction occurs through the development of archegonia and antheridia on the thallus, leading to sporophytes that depend on the gametophytic thallus.

Taxonomic note

Thallosammalet is not a formal taxonomic group but a life-form or growth form used to categorize bryophytes whose body plan is thalloid rather than leafy. It encompasses thalloid liverworts and hornworts and is contrasted with leafy bryophyte forms. Etymology reflects its Swedish roots, combining thallos (Greek for a young shoot or shoot-like tissue) with sammalet (moss).