Pseudoidium javanicum is proposed as a new species based on analyses of 28S, ITS and IGS rDNA sequences, and morphological data. This new species was found on Acalypha wilkesiana var. marginata, A. argentea, and A. cristata collected from Cibodas Botanical Garden, Bogor (West Java Province, Indonesia). Our analyses showed that all these specimens have identical rDNA sequences and similar morphological characteristics. They form a distinct clade separated from other species of Erysiphaceae. Pseudoidium javanicum differs from Erysiphe acalyphae by having shorter conidiophores and foot cells 1–3 times as long as the 0–2 following cells. The conidial size of Ps. javanicum is also smaller than that of E. jatrophae.