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A new species of Diospyros, D. laoensis, from Nam Kading National Protected Area, central Laos, is described and illustrated. It morphologically resembles D. longipilosa of Thailand, D. martabanica of India and Southeast Asia, and D. xishuangbannaensis of China, but is distinguished by its adaxially glabrous midrib, shorter calyx lobes and shorter fruiting pedicel. DNA barcodes of the rbcL and matK regions, a vernacular name and preliminary conservation assessment are also provided. As the species is considered to be endemic to a restricted area which is under threat from deforestation, it is here suggested for assessment under the category of Endangered (EN) within the IUCN Red List of Threatened Species.

This paper presents a re-evaluation of the taxonomic identity of Sciaphila major described from Sarawak, Borneo, Malaysia which has been considered conspecific with S. secundiflora. We revealed that S. major is clearly distinguishable from S. secundiflora s.s. by the arrangement of flowers on rachis (spirally and subdensely arranged vs. secundly and laxly arranged), rachis length in a fully developed inflorescence [(2–)3–6(–7) cm vs. 6–19 cm], tepal length of male flowers (2–2.3 mm vs. 3–4 mm) and the number of perianth segments (more than 6 vs. 6). By spirally-arranged and white flowers, S. major is most similar to S. alba, but is distinguishable by plant height (15–25 cm vs. 25–35 cm in S. alba), rachis length in a fully developed inflorescence [(2–)3–6(–7) cm vs. 8–14 cm)], the number of flowers (usually less than 20 vs. usually more than 20), the arrangement of flowers on rachis (subdensely arranged vs. laxly arranged), the number of male perianth segments (usually more than 6 vs. usually 6) and the condition of floral disc (flat vs. bowl-shaped). We also provide an updated key to the species of Sciaphila distributed in Borneo.

A new species, Gynochthodes honbaensis (Rubiaceae), from Hon Ba Nature Researve, Khanh Hoa Province, southern Vietnam, is described, with a key to the species of Gynochthodes in Vietnam. This species is phenotypically most similar to G. macrophylla distributed in Nicobar Islands, Thailand, and Peninsular Malaysia, but differs in having smaller leaves, and much longer and glabrous peduncles.

Five new species of Syzygium (Myrtaceae), S. honbaense, S. phamhoangii and S. yersinii from Khanh Hoa Province, Vietnam, S. phoukhaokhouayense from Phou Khao Khouay National Protected Area, Vientiane Province, Laos, and S. scabrum from Bung Khla, Phu Wua Wildlife Sanctuary, Buengkan Province, Thailand, are described and illustrated. Photographs, vernacular names and preliminary conservation assessments are provided for them.

Erythroxylum calyptratum, sp. nov. (Erythroxylaceae), from Mt. Fansipan, Hoang Lien National Park, Lao Cai Province, northern Vietnam, is newly described. The new species is characterized by thinly chartaceous leaves with 2–3 mm long petiole, 1–3 flowered inflorescences, downward facing white flowers, well-developed petal appendages (1/3–1/2 length of petals) and entirely free 3 styles. A description, illustrations, DNA barcodes of rbcL and matK and a key to the species of Erythroxylum in Indochina are provided.

Lecanorchis Blume (1856: 188) comprises about 30 species of mycoheterotrophic orchids (Seidenfaden 1978, Hashimoto 1990, Szlachetko & Mytnik 2000, Govaerts et al. 2017) characterized by having numerous, long, thick, horizontal roots produced from a short rhizome, presence of a calyculus (i.e. a cup-like structure located between the base of the perianth and apex of the ovary) and an elongate column with a pair of small wings on each side of the anther (Seidenfaden 1978, Hashimoto 1990). The genus is distributed across a wide area including China, Korea, India, Indonesia, Japan, Laos, Malaysia, New Guinea, Pacific islands, the Philippines, Taiwan, Thailand and Vietnam (Seidenfaden 1978, Hashimoto 1990, Pearce & Cribb 1999, Szlachetko & Mytnik 2000, Averyanov 2011, 2013).

Two new species of Annonaceae, Monoon namkadingense and Neo-uvaria laosensis, from Nam Kading National Protected Area, Bolikhamxay Province, Central Laos, are described and illustrated. DNA barcodes of rbcL and matK, vernacular name and primary conservation assessment are also provided. Both species are considered to be endemic to this area and categorized as Endangered (EN). The distribution of Neo-uvaria laosensis represents northern limit of distribution range for the genus.

A new species of Begonia (Begoniaceae), B. namkadingensis, is described. This species was collected on moist mossy limestone rocks in the Nam Kading National Protected Area in central Laos during our field survey in 2017. The species resembles B. pteridiformis, which is endemic to Peninsular Thailand, but can be distinguished by its smaller habit, fewer and smaller leaves, less hairy stems and leaves, narrower inner dorsal tepal of pistillate flowers, fewer stamens, and smaller fruits.

The genus Thismia Griffith (1844: 221) of the tribe Thismieae, Burmanniaceae sensu APG IV (2016) or Thismiaceae of other authors, represents one of the most species-rich mycoheterotrophic genera and consists of more than 60 species (Jonker 1948, Merckx 2008). Considering that the majority of these species were collected only once (Jonker 1948), and that many new species have recently been discovered, especially from various Southeast Asian countries (e.g., Tsukaya & Okada 2012, Dančák et al. 2013, Nuraliev et al. 2014, 2015, Truong et al. 2014, Chantanaorrapint & Sridith 2015, Li & Bi 2013, Hroneš et al. 2015, Tsukaya et al. 2017, Suetsugu et al. 2017), many more undescribed species are probably still hidden in the tropical rain forests of Southeast Asia.

Herein, Mussaenda recurvata, a new species from Hon Ba Nature Reserve, southern Vietnam, is described and illustrated. This species is morphologically similar to M. longipetala, distributed from southern China to northern Vietnam, in having recurved stipules and densely pilose and puberulent hairs throughout, but differs in its strongly recurved calyx lobes, a shorter corolla tube, and ovate corolla lobes. The species is morphologically heterostylous and it appears to be functionally dioecious. An updated key to Mussaenda species in Vietnam, Laos, and Cambodia is also provided.

A new species, Wikstroemia bokorensis (Thymelaeaceae), from Bokor National Park, Kampot Province, Cambodia, is described and illustrated. This species is morphologically most similar to W. nutans distributed in southern China and Vietnam, but differs in having pubescent branches and leaves, smaller anthers, a single disk scale, and glabrous ovary. DNA barcodes of ITS, rbcL, trnT-F, rps16, and rpl16 regions for the new species are also provided.

Here we describe a new species of the mycoheterotrophic genus Thismia (Thismiaceae), T. brunneomitroides, discovered during a botanical survey in Khao Luang National Park, Peninsular Thailand. Thismia brunneomitroides resembles Thismia brunneomitra from Brunei Darussalam in that both species possess inner tepal lobes that are connate to form a mitre with three projections at the apex and large lateral appendage of the connective. However, it differs in having ivory flowers with twelve pale orange to brownish orange vertical stripes on the perianth tube and slightly dentate lateral appendage of the connective which does not exceed apical part of the connective. Descriptions, illustrations and a key to the 13 species of Thismia in the Thai-Malay Peninsula are provided.

A new species of Primulaceae from Thailand, Lysimachia kraduengensis, is described and illustrated. It is morphologically similar to L. engleri, L. lancifolia, L. laxa and L. sikokiana in having solitary and axillary flowers, a yellow corolla, relatively long pedicels and basifixed anthers. The new species can be distinguished by the combination of its height, leaf texture, petiole, calyx and anther length, and brown coloration on the flowers. In addition, the conservation status, an updated key to Lysimachia species in Thailand, and discussion of the systematic placement of the new species based on the trnL-F marker of chloroplast DNA are provided.