The study of the form and internal structures of plants.
Literally anatomy means to cut something, so plant anatomy commonly mean the internal structures of plant.
However, practically, plant-anatomy is a very broad-term, that includes plant's histology (studying plant-tissue) and tissue-distribution patterns, cellular-level anatomy, especially wall (extracellular matrix)-structures like fibre-patterns, structure of cytoplasmic inclusions like starch-grains , inulin, aleurone, etc. or even organelles like plastid and mitochondria structural variations. as well as large, macroscopic structures, such as topics of plant morphology, like leaf venation, whole leaf, phyllotaxy, branching, etc. and physiognomy, like overall-form, rhizosphere shape, rosette, boulting, etc.
Plant anatomy is not necessarily for internal structures. Various sorts of external structures like types hairs, scales, silica-impregnations, calcareous incrustations, and surface-topography.
Plant-morphology, though sometimes dealt as a separate subject from plant-anatomy, where plant morphology usually more focused to the big-picture as well placement-related concepts like 'apical', 'basal', 'radial', 'axial', etc, and metamorphosis and actual-nature of the organs, practically there are no boundaries in between.
Plant anatomy also discusses the organs/structures for ecological adaptation, and their detailed structure, including mycorrhizae, actinorrhizae, rhizobial-nodules, coralloid roots, parasitic haustoria, succulent's water-storage tissue, floating-tissue etc. It also discusses about structures of plant-disease or Plant-pathology and also about latex, wound-healing, knots, galls etc.
Dendrology, a big branch of plant-anatomy, deals with different aspects of wood, the secondary xylem of plants.
Plant anatomy is closely related to Plant developmental biology and plant physiology.