genus of about 40 species of palmlike cycads (plants of the family Zamiaceae), native to Australia and grown elsewhere as ornamental and conservatory specimens. The genus includes tuberous, fernlike plants and palmlike, columnar trees that grow as high as 18 metres (about 60 feet). The pith is a source of starch, but the seeds are poisonous to livestock. The cones of Macrozamia may grow to be about 0.6 metre long and weigh more than 36 kg (about 80 pounds).