(For John Macadam, M.D., secretary of the Philosophical Institute of Victoria.) Proteaceae. Some ten species of trees or shrubs. Leaves whorled, entire or serrate. Inflorescence a simple raceme, terminal or axillary; flowers small, in pairs, pedicellate; bracts deciduous; perianth usually regular; nectary glands sometimes united around ovary; filaments short, anthers inserted slightly below lamina; ovary with two ovules, style ovoid or clavate at apex, stigma small, terminal. Fruit a hard, globular drupe, indehiscent; seeds one or two. Madagascar to Australia. Z10.

Macadamia species occur on alluvial silts and fertile volcanic soils, in upland tropical (to 1500m) and subtropical climates in their native Queensland and New South Wales, although they are grown for their nuts in the southern US. West Indies, S Africa and are an important orchard crop in Hawaii, where a number of cultivars have been developed. Not all species have edible nuts; those of Macadamia ternifolia give a positive cyanide reaction.

Macadamia species have long been grown as a homestead tree, for shade and ornament, in their native regions, and as a street or avenue tree, developing a clean straight trunk when given space. Macadamia integrifolia, bears creamy white flowers attractive to bees, and a smooth-skinned fruit containing a sweet and crisp white kernel resembling a hazelnut in flavour. Macadamia tetraphylla is similar, with pink flowers and a rough fruit, less commonly grown for commercial production. They are drought resistant ornamentals with attractive glossy foliage, but for good fruting require good drainage and a moderately fertile soil with about 1m of rainfall per annum. Although Macadamia species may survive slight frosts, growth is optimal between 20-25ºC, ceasing below 10ºC and above 30ºC; cold weather can result in loss of the entire crop. They are liable to wind injury when young and on shallow soils are easily uprooted in storms.

In temperate regions, Macadamia may be grown as a foliage ornamental in the cool to intermediate greenhouse, with minimum winter temperatures of 10-15ºC. Grow in a well-drained, medium-fertility mix, preferably in a clay pot with crocks, and keep evenly moist, but not constantly wet when in growth. They stand cutting back well, and should be pruned, potted or top dressed in spring, and may be put outside in summer. Macadamia needs the space of the open garden to develop fruit.

Propagate by fresh husked seed which germinates freely with a bottom heat of 25ºC. desirable cultivars are increased by wedge grafting on to seedling understock, or on to selected stocks which are more resistant to phytophthera root rots. Commercial stocks are expected to begin bearing reasonable crops at 7-8 years and continue to do so for 40-50 years; where commercial considerations are not important Macadamia may fruit for up to 100 years.

MACADAMIA NUT. Medium tree to 20m. Leaves to 14cm, in whorls of 3, oblong to obovate, obtuse apex, young foliage serrate. Flowers white, in pendent cylindrical racemes to 30cm; perianth hairy, to 12mm; style 15mm, tip ellipsoid. Fruit spherical, to 3.5cm diameter; seed hard and brown. Winter-spring. E Australia.

MAROOCHIE NUT. Small tree to 6m. Leaves 16cm, in whorls of 3, obovate to elliptical, irregularly toothed. Flowers pink in 4-20cm, axillary racemes. Fruit not edible. Late winter-spring. E Australia.

QUEENSLAND NUT. Bushy medium tree to 18m. Leaves to 20cm, oblong-obovate, in whorls of 4 (rarely 3 or 5). Flowers creamy pink to purple, in cylindrical pendulous, axillary racemes to 45cm; perianth hairy, to 9mm. Fruit globular, to 3.5cm diameter. Winter-spring. E Australia.