Synaphea platyphylla is a species of flowering plant in the family Proteaceae and is endemic to the south west of Western Australia. It is a tufted shrub with many stems, simple or lobed leaves and spikes of yellow flowers.
Synaphea platyphylla is a tufted shrub with many stems up to long. Its leaves are simple, egg-shaped with the narrower end towards the base, long and wide, or sometimes with two or three lobes, then up to wide, narrowing to a petiole long. The flowers are yellow and moderately openly spaced on a spike up to long on a peduncle up to long. The bracts are broad, long and mostly glabrous. The perianth is ascending, opening widely and , the upper tepal long and wide, the lower tepal long. The stigma is more or less square, about long and wide, and the ovary is covered with soft hairs. Flowering occurs in September and October and the fruit is oval with a beak on the end, long and hairy.
Synaphea platyphylla was first formally described in 1995 by Alex George in the Flora of Australia from specimens collected near Dongolocking Nature Reserve in 1994. The specific epithet (platyphylla) means 'flat-, broad- or wide-leaved'.
This species of synaphea is found in the Narrogin area and near Ravensthorpe in the Avon Wheatbelt and Esperance Plains bioregions of southwestern, Western Australia where it grows in sandy loam in tall shrubland.
Synaphea pinnata is listed as "Priority Three" by the Government of Western Australia Department of Biodiversity, Conservation and Attractions, meaning that it is poorly known and known from only a few locations but is not under imminent threat.