Hardness: The simplest way to describe a wood is to say it's a hardwood or a softwood, but this description can be deceptive: not all hardwoods are hard, and not all softwoods are soft. The hard/soft classification is a botanical one -- hardwoods are flowering trees; softwoods are conifers. Although most hardwoods are harder than most softwoods, there are exceptions.
In general, hardwoods are more valuable than softwoods, because the wood is scarcer. But this isn't always the case -- gum, for instance, is a hardwood that competes in price with softwoods. A more practical way to identify wood is by its grain and color.
Wood grain and color: The cell structure of a tree, different for each species, determines its grain. Hardwoods have tubular cells called vessels, visible as pores in the wood. If the cells are large, the texture of the wood is slightly rough, or open; a filler may be needed to smooth the surface. If the cells are small, the texture is smooth; these woods, described as close-grained, don't require filling. Oak, walnut, ash, mahogany, rosewood, and teak are all open-grained woods; beech, birch, maple, cherry, satinwood, gum, and poplar are close-grained. Softwoods don't have vessel cells, but for all practical purposes can be considered close-grained.
All trees have annual growth rings, made up of the cells formed during each year's growing season. The types and arrangement of the cells determine how the wood looks. There are woods with subdued and with clearly defined grains; there are straight grains, stripes, swirls, waves or curls, ripples, eyes, and mottled effects. There are colors from white and pale yellow through red, purple, and black. Every species has its own particular grain and color, and although they vary from tree to tree, these characteristics can almost always be used to identify the wood.
Furniture woods are chosen and valued for the character of their grain and color. Hardwoods usually have a richer and finer-textured grain than softwoods, but there are rich grains of all colors and patterns. Woods with very distinctive patterns are usually more valuable than woods with subdued or indistinct patterns, and the weaker-grained woods are often stained to give them character. This is why the old finish must be completely removed before you can tell for sure what wood a piece of furniture is made of.