This is a stately evergreen shrub with spiny, leathery leaves, of a dark green hue. In late autumn and winter, it sends up long, upright flowering spires of tiny, yellow, clustered bells, which have a soft scent. Blue-black berries will follow. The shrub grows to 2-3 m, and can eventually get to 3 m wide over time. It comes from China and belongs to the Berberidaceae family of plants, which also includes the genera Berberis and Nandina. Mahonia do very well in full or part shade, which makes them very useful in gardens where there are lots of trees! The shrub enjoys fertile, well-drained soil with added organic matter. It is quite frost-hardy, but will grow in a range of climates, including in Sydney. It doesn't require heavy pruning, just trimming the branches lightly to shape. To rejuvenate old plants, very woody canes can be cut out at ground level in spring.
The exquisite Corsican hellebore (Helleborus argutifolius), which has tall stems holding clusters of large, rounded green flowers in winter, is in bloom at the same time as the Mahonia, and its serrated-edged, veined foliage has a similar look and colour, so it could be an excellent underplanting specimen. Like most hellebores, it grows well in shade. It self-seeds gently to form a little colony after a few years.
Note: I have previously referred to this plant as Mahonia japonica, in error.