Acalypha lyonsii, commonly known as Lyon's acalypha is a shrub in the spurge family Euphorbiaceae that is only found in the vicinity of Cairns, Queensland, Australia.
Acalypha lyonsii is a shrub up to tall. The leaves are arranged alternately on the twigs and measure up to long by wide. They have rounded teeth on the margins and 4 or 5 lateral veins either side of the midrib. Flowers are produced from the - male flowers are less than long and carried on a spike, female flowers are solitary, about diameter and subtended by a much larger bract. The fruit is a 3-lobed capsule about long and wide.
This species was described in 1994 by the Queensland botanist Paul Irwin Forster based on material collected by Christopher Lyons in 1992 on the Lamb Range southwest of Cairns. The species is named after him.
Acalypha lyonsii grows as an understorey plant in rainforest near Cairns, at altitudes from sea level to about .
This species is listed by the Queensland Government's Department of Environment, Science and Innovation as vulnerable., it has not been assessed by the International Union for Conservation of Nature (IUCN).