Currently, approximately 250,000 individual species have been identified and ascribed to the kingdom Plantae (the plant kingdom). The range of diversity suggested by such a large variety of species can be easily substantiated with a few examples such as microscopic duckweed, gargantuan Redwood trees, and carnivorous Venus flytraps.

Despite the vast diversity of the plant kingdom, tissues comprising the leaves, roots, and stems of all plants are categorized into just three basic tissue systems: the dermal, ground, and vascular layers.

Dermal tissues are the outermost layers of the plant. The primary dermal tissue, the epidermis, is found on young parts of a plant such as new growth of stems and leaves. Epidermis is eventually replaced by the secondary periderm, which is composed of phellem, phellogen, and phelloderm. Cork and bark are common examples of periderm tissue.

Vascular tissues, which occupy the innermost regions of the plant, are composed of xylem and phloem. Xylem, which is rather sturdy and helps brace and support the weight of the plant, delivers water and nutrients (generally absorbed in the roots) to the food-producing regions of the plant. Phloem, a much softer tissue, distributes the food throughout the plant. Vascular systems may not be present in the more primitive plants, such as mosses and other Bryozoans.

Ground tissues reside amid the dermal and the vascular tissue and comprise the bulk of the plant body. While some of the material functions merely as filler, other portions of this middle layer may be host to integral physiological functions of the plant. For example, most photosynthesis typically takes place inside the ground layer of the leaves. The main constituents of the ground tissue layer are three generalized tissue types: parenchyma, collenchyma, and sclerenchyma. These cells are present in different quantities throughout all three tissue systems, but the highest concentration is located in the ground layer. Parenchyma cells have thin cell walls and are the most generalized in function, performing such duties as photosynthesis, food storage, and cellular respiration. Collenchyma cells are distinguished by thicker, uneven cell walls. These elongated cells form in strands, most commonly found in the younger structures of the plant. Sclerenchyma have thick but even cell walls, and their strength provides structural support throughout the plant, especially in the roots and stems.