Fortunella margarita 'Nagami' is an evergreen shrub or tree grown for its ornamental qualities rather than it's fruit.
They make good garden specimens being compact with attractive dark green foliage and pretty white, fragrant flowers in spring.
The subsequent orange fruits are oval shaped and edible, though rather tart to taste but can be made into preserves.
They make excellent large tub specimens on a patio where they can be kept more compact and look great as a standard.