Flowers are produced in a long slender simple raceme 5–30 cm long, the individual flowers 10–15 mm long, white to pink or purple, with four tepals.
The Association of Societies for Growing Australian Plants (ASGAP) notes that macadamia has the distinction of being the only Australian native plant to be grown as a major commercial food crop. Two species, M. integrifolia and M. tetraphylla (and their cultivars), are grown in a number of countries including the United States (Hawaii, California), southern Africa and central America.
Wikipedia notes that macadamia has a disjunct distribution, some being native to eastern Australia (seven species), others in New Caledonia (one species M. neurophylla) and Indonesia Sulawesi (one species, M. hildebrandii).

Photo: Robert Whyte
Fruit
Despite M. integrifolia and M. tetraphylla being edible, the nuts of some of the other species are poisonous, including M. whelanii and M. ternifolia; the toxicity is due to the presence of cyanogenic glycosides.
The two species of edible macadamia readily hybridise, and M. tetraphylla is threatened in the wild due to this. Wild nut trees were originally found at Mt Bauple near Maryborough in SE Queensland, Australia.
The genus is named after John Macadam, who was a colleague of the botanist, Ferdinand von Mueller, who first described the genus. Common names include Macadamia, Macadamia nut, Queensland nut, Bush nut, Maroochi nut and Bauple nut; Indigenous Australian names include Kindal Kindal and Jindilli.

Photo: Robert Whyte
Seedling in plant protector
The first commercial orchard of macadamia trees was planted in the early 1880s by Mr Charles Staff at Rous Mill, 12 km south east of Lismore, New South Wales, consisting of M. tetraphylla. Besides the development of a small boutique industry in Australia during the late 19th and early 20th century, macadamia was extensively planted as a commercial crop in Hawaii from the 1900s. The Hawaiian-produced macadamia established the nut internationally. According to the Australian Macadamia Society website in 2021, Australia is now the world’s major producer of macadamia nuts with an annual crop of 50,000 tonnes. The Society is making efforts to improve the genetic diversify of the crop.
Macadamia species are used as food plants by the larvae of some Lepidoptera species including Batrachedra arenosella (Coconut Moth).
References: Wikipedia, Association of Societies for Growing Australian Plants (ASGAP)

Photo: Robert Whyte