Felted - Botanical Use of The Term

Botanical Use of The Term

In botanical terminology "felted" typically is defined in terms such as "matted with intertwined hairs". However, plants may be covered in several different ways, and several different terms have been coined to describe them. Not all textbooks use the same terms, or use them in the same way. The term "felted" is commonly used in describing any part of a plant covered with dense white fur, whether tangled or not. Part of the reason is the fact that plants themselves very so much that there seldom is much practical value to trying to be too precise; for example there is no clear boundary to separate terms such as "felt(ed)", "arachnoid", "indumentum" and "tomentose" and usages vary.

In botany, as opposed to mycology, "felted" seldom refers to internal tissues, but rather to furriness on the outside of leaves or stems. The function of the covering is always protective, sometimes against grazing or browsing animals, sometimes against wind or windblown sand, sometimes against intense sunshine or ultraviolet, and sometimes against drought and desiccation. Two illustrative examples are: Oldenburgia grandis, and Senecio haworthii. The former is a tree that grows in moderately harsh circumstances, but with a reasonable amount of seasonal rain. Its leaves are large, being broad and typically about 30 cm long. While growing to their full size they are vulnerable, so it is quite plausible that being felted protects them from browsers, ultraviolet, drought, and heat. Once their tissues have hardened and become rich in fibre and tannins, they can afford to lose their felt. In this respect they resemble many other plants whose leaves pass through vulnerable phases as they mature, though not all strategies are based on felt.

Senecio haworthii grows under far more dramatically arid conditions than Oldenburgia; its native habitat also is hotter and with a higher irradiation intensity. The plant is fairly poisonous, so it is not much browsed, though some caterpillars will eat its succulent leaves. Accordingly its need for protection does not change much at any time of the year and some leaves will survive for several years, retaining their felting throughout.

In Cephalocereus senilis (old man cactus} radial spines grow into a tangled coating of spectacular white hair that conceal both the green tissue and the formidable sharp central spines beneath. It is only marginally felted, but forms a powerful simultaneous protection against intense radiation, wind, frost, and herbivores of various sizes. The woolly masses of fibres on such cacti have been used as stuffing for pillows and for similar applications.