There aren't many shrubs that are truly dwarf enough for a rock garden, especially in today's smaller gardens, but this is one of the best. A variety of Berberis x stenophylla, 'Corralina Compacta' forms a small, dense shrub of dark green, evergreen leaves, the branches almost drooping with masses of these glorious orange-yellow flowers in early summer. And like all Berberis, it's prickly!
Although very dwarf and slow-growing, this Berberis (like any other) won't object to hard pruning if it ever does outgrow its space, but that won't happen for several years. Ultimate height is around 60cm (2 ft) but that is a variable figure and the above advice on pruning negates it.