Pentanisia prunelloides grows several hairy stems to a height of 60 cm. Its leaves are opposite, stalkless and broadly lanceolate or ovate. Clusters of spring and summer flowers grow on long, sturdy stalks. They are blue or mauve in colour with five narrow corolla lobes.
There are two forms of the flower style, either a long one in a pin flower, or a short one where the flower is called a thrum. When the stamens are long, the style is usually short and vice versa, a feature of this plant's polymorphism. Some plant species are even tristylous, displaying three different morphs or flower forms, such as Oxalis pes-caprae.
Kenya and Ethiopia have a similar looking Pentanisia species, P. ouranogyne with narrow leaves and very similar flowers (Manning, 2009; Wikipedia; Blundell, 1987).