Pennantia baylisiana is a species of plant in the Pennantiaceae family (Icacinaceae in older classifications). It is endemic to the Three Kings Islands, New Zealand, where only one plant is known to exist. It is threatened by habitat loss. Pennantia baylisiana was listed as one of the world's rarest plants by The Guinness Book of Records. The single tree known in the wild grows on a scree slope on the northern face of Great Island in the Three Kings group off Cape Reinga, New Zealand. The species was discovered in 1945 by Professor Geoff Baylis of the University of Otago.