A xylotheque or xylothek is special form of herbarium that consists of a collection of authenticated wood specimens. It is also known as a xylarium. Traditionally, xylotheque specimens were in the form of book-shaped volumes, each made of a particular kind of wood and holding samples of the different parts of the corresponding plant. While the terms are often used interchangeably, some use xylotheque to refer to these older collections of wooden 'books' and xylarium for modern collections in which some or all of the specimens are in simpler shapes, such as blocks or plaques with information engraved on their surfaces. Many countries have at least one xylotheque with native flora, and some also house flora from other parts of the world. They are valuable to specialists in forestry, botany, conservation, forensics, art restoration, paleontology, archaeology, and other fields.

A herbarium is a collection of preserved plant specimens and associated data used for scientific study.