Acalypha rubrinervis (string tree or stringwood) is an extinct plant in the spurge family (Euphorbiaceae), from the island of Saint Helena in the South Atlantic Ocean.

The genus to which it belongs, Acalypha, is a large one and includes island endemics as well as weeds and ornamentals.

A. rubrinervis was a shrub or thicket growing on the central ridge of St Helena above 600 m elevation.

Acalypha rubrinervis is closely related to Acalypha reticulata of the Seychelles, Madagascar, Comoros, Mauritius and Reunion, but it is quite distinct from that species in general appearance, leaf shape, the red colouring, smoot carpels and the very large female bracts.

Dr William Roxburgh remarked that it was a beautiful small tree, a native of elevated parts of the south face of Diana's Peak, called the string-tree on account of its numerous beautiful red male spikes, which were hanging in great profusion from every twig.