Thallus
A plantlike body not differentiated into true roots, stems, and leaves. Thalli occur in algae, fungi, lichens, and some nonvascular plants.
Plant anatomy: The study of plant structures and their organization, from cells and tissues to organs. Its root–stem–leaf framework clarifies what thalli lack.
Algae: A diverse group of photosynthetic organisms, mostly aquatic, that lack the defining structure of land plants. Many algae have thalli, ranging from single sheets to complex forms.
Rhizoid: A hairlike or threadlike structure that anchors some plants, algae, and fungi or absorbs water and nutrients. Rhizoids can anchor a thallus without functioning as true roots.
Cormus: A plant body differentiated into true roots, stems, and leaves. It names the organized body plan that contrasts with a thallus.
Plant tissue: A group of plant cells organized to perform a shared function. Thalli may lack the specialized tissues that support complex plant organs.
Fungi: A kingdom of organisms that absorb nutrients and typically grow as networks of microscopic filaments. Some fungi form compact thalli rather than conspicuous filament networks.
Holdfast: An anchoring structure that attaches an alga or other organism to a surface. Seaweed thalli use holdfasts to resist currents without drawing nutrients like roots.
Cormophyte: A plant with a differentiated body containing true roots, stems, and leaves. Cormophytes possess organ-level differentiation absent from thalli.
Vascular tissue: Plant tissue that transports water, minerals, and sugars through xylem and phloem. Its absence helps explain why many thalli remain small and structurally simple.
Lichen: A stable association between a fungus and a photosynthetic partner, usually an alga or cyanobacterium. Its visible body is a composite thallus built by the partners.