Mediusella bernieri grows as a shrub or small tree up to tall. It has a trunkdiameter of up to. Its bright green leaves are ovate in shape and measure up to long. The plant's flowers are usually in inflorescences of two or three flowers, each with white to yellow petals. The ovoid fruits measure up to long. Mediusella bernieri flowers and fruits from February to July.
Mediusella bernieri is in decline due to habitat destruction from activities such as agriculture, mining, fires and wood harvesting. In 2019, it was assessed by the IUCN as Endangered. Although four subpopulations of the species are within the protected areas of Andavakoeira-Andrafiamena and Loky Manambato, the species' decline continues due to the above activities.