Family Proteaceae > Subfamily Grevilleoideae > Tribe Macadamieae > Subtribe Macadamiinae.
There are four species all native to south eastern Queensland and New South Wales.
The species are Macadamia integrifolia, M. ternifolia, M. tetraphylla and M. jansenii.
Macadamia integrifolia and M. tetraphylla are grown commercially for their nuts.
Nuts from M. jansenii are toxic.
There are a lot of hybrids between all 4 species.
They are 2 m shrubs or trees up to 40 m high sometimes with buttressed bases.
Leaves are mostly in whorls (or pseudowhorls) and on petioles.
They are elliptic, lanceolate or obovate and up to 30 cm long and 13 cm wide.
The margins can be entire or toothed.
Terminal or axillary inflorescences are drooping, unbranched spikes (racemes).
They are up to 30 cm long with bisexual flowers in pairs or scattered.
At the base of the flowers is a bract that may remain or fall off.
The 4 white, cream or pink tepals are around 12 mm long.
They are initially fused into a tube.
The distal part splits and the tepal tips curl back.
The short stamen filaments are inserted into the dilated tips of the tepals.
The tissue between the anther sacs has a short appendage.
The fused hypogynous glands form a ring around the base of the ovary.
The hairy ovary, with 2 ovules, may or may not be on a short stalk.
The style is straight with a slightly expanded tip with the stigma and pollen presenter.
The fruit are very hard, woody follicles that remain on the tree until ripe.
They are roughly spherical with an apical horn.
They may or may not open at maturity to release a, usually single, seed.
Generally speaking trees with toothed leaves in whorls of 4 and densely hairy inflorescences are M. tetraphylla.
M. integrifolia and M. ternifolia typically have leaves in whorls of 3.
M. integrifolia has leaves with blunt tips, white flowers and fruit 2.5 cm or more across.
M. ternifolia has leaves with pointed tips, pink flowers and fruit 2 cm or less across.
There are variations on these in each species.
Macadamia ternifolia is the type species.
They are small trees, up to 8 m high, with multiple stems.
The leaves are typically in whorls of 3 and on stalks up to 1 cm long.
The narrowly ovate or elliptic blades are up to 12 cm long and 4 cm wide.
The tips are pointed, the edges slightly wavy and there are coarse teeth.
They are dull green above and paler underneath.
New growth is pink to red and branches have small white lenticels.
Terminal inflorescences are up to 20 cm long and the axis may have hairs.
Flowers have pink tepals up to 8.5 mm long with hairs on the outer surface.
There are bracts up to 5 mm long at the base of the pedicels which are up to 3.5 mm long.
The 2 mm dilated tepal tips hold the 2 mm anthers.
Most of their 7 mm long filaments are fused to the tepals.
The ovary, up to 1 mm high, has a style up to 10 mm long.
There are hairs on the ovary.
The brown or greyish, smooth, roughly spherical follicles are around 2 cm wide.