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Background A large number of secondary metabolites can be obtained from plants used for traditional medicine in two related genera (Ixora and Greenea) in the subfamily Ixoroideae (Rubiaceae), but there are only a few detailed studies on their bioactivities. Therefore, the main goals of this study were to determine the antibacterial activities of lipophilic extracts from plants of some Ixora and Greenea species native to Thailand, and to isolate some pure compounds from those extracts. Moreover, we compared the occurrence of compounds in different plant parts of samples from different habitats to better understand their variation. Methods A total of 56 lipophilic extracts were obtained from the leaves, stem bark, and root bark of eight Ixora and two Greenea species collected at various locations in Thailand. Isolated compounds were identified using nuclear magnetic resonance. Antimicrobial activities were evaluated against four Gram-positive and nine Gram-negative human pathogenic bacterial strains. Results Extracts from I. javanica, I. nigricans, I. brunonis, and G. montana, along with isolated scopoletin, exhibited antibacterial activities against Gram-positive methicillin-resistant Staphylococcus aureus ATCC 43300, with minimum inhibitory concentration values ranging from 64 to 256 µg/mL. The occurrence of scopoletin, isofraxidin, and geniposidic acid in lipophilic extracts showed some variation among different plant parts and species. Conclusions Lipophilic extracts of Ixora and Greenea species have the potential to be developed as anti-Gram-positive agents, in particular to counter infections of methicillin-resistant S. aureus strains. The chemical profiles showed differences between floristic regions but similarity within the same plant parts.

A new species is described, Lithocarpus orbicarpus Strijk, collected from Ton Pariwat Wildlife Sanctuary, Mueang district, Phang Nga Province in the Peninsular Floristic Region of Thailand. We provide the first technical illustrations and colour photographs of the new species, as well as a description of its conservation status and the collecting locality. The species can be easily distinguished by its unique orbicular acorns, each covered with a dense pattern of irregularly placed scales, which completely conceal the nut, except for a tiny apical pore, and which are arranged in a dense cluster on an erect woody spike. We also provide an amendment to the existing diagnostic key to Lithocarpus, and discuss important differences with morphologically similar species found in Thailand and the surrounding region.

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Lasianthus purpureocalyx Napiroon, Chamchumroon, Balslev & Chayamarit sp. nova (Rubiaceae) from the Khao Ngon Nak hill (Aaonang sub-district, Krabi province, Thailand) is described and illustrated. It is similar to L. subcalvus but differs from it in having narrowly lanceolate, 2-3.5 ¥ 12-16 cm leaves, 6-7 corolla lobes, and globose fruits (versus leaves oblong-elliptic 5-7 ¥ 16-23 cm, corolla 4-lobed, fruit fusiform). It also resembles L. purpureus in leaf morphology, but differs from it in having flowers in sessile cymes instead of fascicular pedicels. Its leaf morphology also bears resemblance to that of L. foxworthyanus, but differs from it in having a purple tubular calyx with 6-7 lobes and calyx limb that are shallowly curved or nearly entire (versus a pale green campanulate calyx with 4-5 lobes and 5 calyx limb lobes that are lanceolate).