Thorns, spines, and prickles
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In plant morphology, thorns, spines, and prickles, and in general spinose structures, are hard, rigid extensions or modifications of leaves, roots, stems, or buds with sharp, stiff ends, and generally serve the same function: physically defending plants against herbivory.
Prickles on a blackberry branch
(A) Thorn or spine (B) Prickle
Smooth, featureless Citrus thorn.
Gymnosporia buxifolia thorn, its leaves, nodes, and emergence from an axillary bud demonstrating its nature as a branch.
Trichome
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Trichomes are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant is an indumentum, and the surface bearing them is said to be pubescent.
Flower bud of a Capsicum pubescens plant, with many trichomes
Fossil stellate hair (trichome) probably of an oak, in Baltic amber; image is about 1 mm wide.
Sticky trichomes of a carnivorous plant, Drosera capensis with a trapped insect, contain proteolytic enzymes
Glandular trichomes on Cannabis, rich in cannabinoids