What kind of wood is this? It is made of a patchwork of wood pieces.
It looks like finger-jointed and edge-laminated pine. If you look at the edge you can probably see the characteristic zigzag cut pattern.
It's commonly used for "paint grade" millwork such as closet shelf cleat. It's cheaper and more stable than clear pine, but you may see the grain variation through light paint coatings. Try to avoid making any end cuts directly through the joints.