During an evaluation of the diatom diversity and water quality of a small brook near Morogoro (Tanzania), an unknown Planothidium species was observed that could not be identified using the currently available literature. The past 10 years, a large number of Planothidium species has been revised resulting in a better characterisation of some well-known taxa such as P. lanceolatum (Brébisson ex Kützing 1846: 247) Lange-Bertalot (1999: 287), P. frequentissimum (Lange-Bertalot 1993: 4) Lange-Bertalot (1999: 282) and P. delicatulum (Kützing 1844: 75) Round & Bukhtiyarova (1996: 353), but also in the description of a lot of new species (Compère & Van de Vijver 2009, Jahn et al. 2017, Kulaš et al. (2020), N’Guessan et al. 2014, Stancheva 2019, Stancheva et al. 2020, Van de Vijver et al. 2013, 2018, Wetzel et al. 2013, 2014, 2019). Several of these studies dealt with Planothidium species from the African Continent. Compère & Van de Vijver (2009) analysed and illustrated the type material of P. engelbrechtii (Cholnoky 1955: 16) Round & Bukhtiyarova (1996: 353), whereas N’Guessan et al. (2014) discussed the morphology and taxonomic history of two species formerly described by Carter & Denny in 1982: P. miotum (J.R.Carter & Denny 1982: 286) Lange-Bertalot (1999: 278) & P. piaficum (J.R.Carter & Denny 1982: 286) C.E.Wetzel & Ector (in N’Guessan et al. 2014: 460), completed with the description of P. comperei C.E.Wetzel et al. (in N’Guessan et al. 2014: 456), a new Planothidium species from Ivory Coast.