According to recent research data from 2003 to 2019, about 220 new species and approximately 360 new records of plants have been reported in Myanmar (Yang et al., 2020). Floristic studies conducted just before the coronavirus disease 2019 pandemic, for example, have led to the discovery of a new orchid species Dendrobium popaense T. Yukawa & Nob. Tanaka (Orchidaceae) (Yukawa et al., 2022), and even of a new genus Myanmaranthus Nob. Tanaka, Suksathan & K. Armstr. (Marantaceae) (Tanaka et al., 2022). Despite the current geopolitical conflicts in the country, the Myanmar plant checklist is continuously being updated (e.g., Nagahama et al., 2023), mostly based on floristic expeditions and collections of local botanists, in collaboration with various scientists from America, Europe, and Asia. The most recent account of vascular plants in the country number to about 16,200 taxa (Aung et al., 2023).

This work is our second report of newly-recorded flowering plants collected from Southern Shan State in eastern Myanmar, specifically from Panlaung-Pyadalin Cave Wildlife Sanctuary (PPCWS) and the surrounding areas in Ywangan Township (see Kang et al., 2018). PPCWS is a limestone area which is one of the six protected areas in Shan State, out of the 43 total conservation areas and national parks in the country (Kang et al., 2021a). Botanical investigations in this region are seen to gradually bridge the floristic gap between China’s Yunnan Province and Thailand’s northern region. For instance, recent floristic study published from PPCWS and surrounding areas accounted 243 species of seed plants (Kang et al., 2021a), and a number of new species (Kang et al., 2021b; Fujiwara et al., 2022). Hence, in terms of regional comparison, Shan State has become the fourth-highest contributor to newly reported taxa in Myanmar, with at least 15 new species and 55 newly recorded taxa since 2000 (Yang et al., 2020). The rich plant diversity in this region can be attributed to the diverse climates, forest types (e.g., lowland evergreen forests, dry deciduous forests), and elevational variations (150–1,555 m) (Beffasti and Galanti, 2011; Kang et al., 2021a), as well as its accessibility to plant researchers both local and international.

With the support of the National Institute of Biological Resources (NIBR) of the Republic of Korea and Ministry of Natural Resources and Environmental Conservation (MONREC) of Myanmar, we conducted joint floristic surveys on PPCWS and Ywangan areas from 2017 to 2019. Here, we report an addition of four new plant records, including their taxonomic information and photographs. We also provide their original distribution and specimen information, and brief taxonomic and/or phytogeographic notes when needed.

The botanical survey was conducted five times from February 2017 to February 2019 in the areas shown in Fig. 1. Newly reported taxonomic groups in Myanmar were verified using data from sources such as the Flora of Thailand and the Flora of China. Voucher specimens for each identified species were collected and stored in the Herbarium of Hallym University (HHU) and/or the National Institute of Biological Resources (KB) in South Korea. The new Myanmar records reported here are arranged in alphabetical order by family names, along with their voucher information. Major synonym (s) of each species are also provided. The distribution of these species in PPCWS and adjacent areas is mapped in Fig. 1.

The four new plant records for the flora of Myanmar were found to belong to four genera in four families of flowering plants (Fig. 2). Among them, Aeschynanthus minutifolius D. J. Middleton (Gesneriaceae) is found to be endemic to Thailand. Additionally, we report Vincetoxicum rotundifolium (Buch.-Ham. ex Wight) Kuntze (Apocynaceae), and Amischotolype neoscandens Idrees (Commelinaceae). A notable discovery is Trailliaedoxa gracilis W. W. Sm. & Forrest (Rubiaceae), the only member in its genus that is only found in Yunnan and Sichuan, China. Taxonomic information for each of these species are provided below.

1. Vincetoxicum rotundifolium (Buch.-Ham. ex Wight) Kuntze, Revis. Gen. Pl. 2: 425, 1891 (Apocynaceae) (Fig. 2A)

Tylophora rotundifolia Buch.-Ham. ex Wight, Contr. Bot. India 50, 1834.

Specimens examined: MYANMAR. Southern Shan State, Ywangan Township, 21°07′34.9″N, 96°19′ 07.8″E, elev. 284 m, 30 Jun 2019, Kim et al. MM-7341 (HHU, KB).

Type: India. Dongtola, 24 Apr 1808, Buchanann-Hamilton, Francis, 759 (isosyntype: E). China. Sha Po Shan, Taam Chau District, 24 May 1928, Tsang, Wai-Tak, 481 (isotype: MO photo!).

Distribution: Bhutan, China, East Himalaya, India, Nepal, Thailand (Li et al., 1995; POWO, 2024).

Note: The species was collected in a lowland forest with red soil, a subtropical forest around a lake created by a dam in PPCWS. V. rotundifolium is a trailing herb, with hairy stems that grow up to 3 m long, and sometimes twining apical part. Compared to previous descriptions, the petiole was observed to be as long as 8 mm, and leaf blades to ca. 11.5 × 9.5 cm. The apex was reported as short mucronate or round, but retuse ones were also observed. The corolla is greenish-yellow and is more than twice as long as the calyx.

2. Amischotolype neoscandens Idrees, Kew Bull. 77: 577, 2022 (Commelinaceae) (Fig. 2B)

Amischotolype scandens (D. Y. Hong) C. K. Lee, Fuse & M. N. Tamura, Bot. J. Linn. Soc. 198: 127, 2021; Porandra scandens D. Y. Hong, Acta Phytotax. Sin. 12: 462, 1974.

Specimens examined: MYANMAR. Southern Shan State, Ywangan Township, 21°15′59.3″N, 96°27′49.9″E, elev. 1,759 m, 19 Aug 2018, Kim et al. MM-6860 (HHU, KB).

Type: China. Dah meng-lung, Che-li, Jun 1936, C. W. Wang, 77909 (isotype: A photo!).

Distribution: China, Laos, Thailand, Vietnam (Hong and DeFilipps., 2000; POWO, 2024).

Note: This species was previously classified into the genus Porandra, which was later circumscribed within the genus Amischotolype, creating a new name combination A. scandens (D. Y. Hong) C. K. Lee, Fuse & M. N. Tamura (Lee et al., 2021). The name, however, was found to be a homonym of A. scandens Burg & E. Bidault (Burg and Bidault, 2020), hence is once again replaced with A. neoscandens Idrees (Idrees, 2022).

3. Aeschynanthus minutifolius D. J. Middleton, Edinburgh J. Bot. 64: 404, 2007 (Gesneriaceae) (Fig. 2C)

Specimens examined: MYANMAR. Southern Shan State, Ywangan Township, 21°15′52.5″N, 96°27′41.2″E, elev. 1,638 m, 18 Aug 2018, Kim et al. MM-6849 (HHU, KB).

Type: Thailand. Siam, Raheng, Sep 1924, Eryl Smith, s.n. (type: ABD, isotype: BM photo!).

Distribution: Thailand (Middleton, 2007; POWO, 2024).

Note: Middleton (2007) mentioned that it was discovered in Tak Province, Thailand, and that it is highly likely to be distributed in Myanmar as it is near the Myanmar border. In this study, we report on its discovery in Shan State, which is a region adjacent to Thailand. Compared to the existing description, the leaf blades of this species were observed to be ovate, in addition to being obovate and elliptic. The corolla was also found to be red and grows up to ca. 3 cm long.

4. Trailliaedoxa gracilis W.W. Smith & Forrest, Notes Roy. Bot. Gard. Edinburgh 10: 75, 1917 (Rubiaceae) (Fig. 2D)

Specimens examined: MYANMAR. Southern Shan State, Ywangan Township, 21°15′31.1″N, 96°25′07.2″E, elev. 1,392 m, 17 Aug 2018, Kim et al. MM-6773 (HHU, KB).

Type: China. Mts. in the N.E. of the Yangtze bend, Jul 1913, G. Forrest, 10535 (syntype: E, isosyntype: A photo!, HBG); Mts. in the N.E. of Yangtze bend, Aug 1913, G. Forrest, 10713 (syntype: A, E); Mountains of the Chungtien plateau, Jul 1914, G. Forrest, 12638 (syntpe: E, isosyntype: HBG).

Distribution: China (Chen and Taylor, 2011; POWO, 2024).

Note: This species belongs to a genus endemic to China. It has the form of a small shrub and is found around the Yangtze River in the Sichuan and Yunnan Provinces of China. This erect subshrub, which is ca. 40 cm tall, has hairs throughout, including on the stems, leaves, calyx, and corolla. The leaves are obovate, elliptic, and are less than 1 cm long. The flower buds can vary from light green to white.