A general survey is given of the morphology and anatomy of the genus Placynthium. The species: aspratile, flabellosum, nigrum incl. v. tantaleum, petersii, subradiatum, and stenophyllum are described in detail. The following new combinations are made: Placynthium filiforme, Placynthium aspratile, Placynthium subradiatum f. coerulescens, and Synalissa subnigra. The new variety Placynthium stenophyllum v. isidiatum is established.