Ordinarily, the first -- and frequently hardest -- difficulty in origami design comprises extracting, from (usually) four large blunt corners of a sheet, enough points matching the appendages (arms, fingers, legs, tail, wings, antennae, pincers and so on), some considerably long and thin, of common subjects, which mostly have bilateral symmetry.
An origami rose makes a very different challenge. Its appendages are not long, but wound in spiral layers. A good paper rose belies its folded origin, its curves hiding the original edges.
To folders worldwide, Japanese mathematician Toshikazu Kawasaki is better known due to his series of origami roses, all using a characteristic twisting technique. The "classic" rose is truly an icon of modern paperfolding, a breakthrough model whose spiral symmetry and delicately curved petals contrasted with the straight lines and sharp angles common in previous works. Diagrams are available, e.g. in [KT87] and [ORU4], pages 121-123. Kawasaki developed several variations, including tesselations featuring several flowers folded from a single sheet.
A much more elaborated rose was published in [Kaw98]. It was also diagrammed by Winson Chan.
Finally, a lesser-known version is a tubular flower with optional leaves folded from a separate sheet. Diagrams are available in both [Ka??] and [Kan97], pages 283-287. I rediagrammed this model here. A slightly different version without a base is included in [Kaw98] and named a rose bud; it is shorter, with a larger calyx.
Some information about diagram availability was researched and provided by Julia Palffy.