Six new species of Friesodielsia (Annonaceae) are described and illustrated, seven species are documented for Thailand for the first time, and Oxymitra fornicata (Roxb.) D. Das var. glabra is raised to species rank as Friesodielsia andamanica. These additions bring the species diversity of Friesodielsia in Thailand to 16 species. A key to the Thai species is provided.

Two new Friesodielsia species (Annonaceae) from Peninsular Thailand, F. betongensis and F. chalermgliniana, are described and illustrated. The addition of these raises the total number of Friesodielsia species in Thailand to 18. A conservation assessment for each new species and an identification key for all Thai species are provided.

The three species of Alysicarpus known from Thailand are described with notes on their distribution and ecological data, vernacular names and photographs. They are Alysicarpus bupleurifolius, A. rugosus and A. vaginalis. A key for the identification of the three species is provided. A lectotype for Alysicarpus wallichii is selected here.

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Clerodendrum angustipetalum (Lamiaceae), an endemic species to Narathiwat province, southern Thailand, is described and illustrated as a species new to science. It is similar to C. nutans in having an elongate pendulous inflorescence, but   essentially differs in the thicker leaf texture (subcoriaceous vs membranaceous), the calyx tube being almost twice as long and the corolla lobes being half as broad. In addition, the new species has longer calyx lobes, corolla lobes and stamens.  The conservation status of this species is assessed as Critically Endangered (CR, B2a + b(ii, iii)+C2ai+D)  due to being known from a single locality with a small population of less than 50 individuals. A morphological comparison between similar species and an updated key to Clerodendrum species with pendulous inflorescences from southern Thailand is also presented.