Thielaviopsis is a small genus of fungi in the order Microascales,[1] and family Ceratocystidaceae.

[2] The genus includes several important agricultural based pathogens.

The most widespread is T. basicola, the causal agent in several root rot diseases of economically important crop species including cotton and a variety of vegetables.

The genus name of Thielavia is in honour of Friedrich Joachim Sigismund von Thielau (1796–1870), who was a German forester and landowner in Breslau.

[3] As accepted by Species Fungorum;[2] Former species;[2] (assume family Ceratocystidaceae if not mentioned)