The family Cyperaceae is the third largest family within monocots, after Orchidaceae and Poaceae, with ca. 90 genera and ca. 5 500 species^[1]. The family has an almost cosmopolitan distribution, and occupies a broad range of habitats from rain forests to tundra^[2-4]. It is phenotypically very diverse in the tropics, and its generic diversity is greatest in the tropics as well^[5-7].

The genus Actinoschoenus Benth. is one of the tropical genera of Cyperaceae, with 8 or 4 species, distributed from tropical Africa through S and SE Asia to N Australia^{[1, 8]}. It was sometimes merged into the genus Fimbristylis Vahl before^[9-10]. Nevertheless, its embryo type is quite different from that of Fimbri- stylis, and Actinoschoenus is widely accepted as a separate genus nowadays^{[1, 5, 11-13]}. According to the literatures, the genus was found in Cambodia, China, India, Indonesia, Malaysia, Philippines, Siri Lanka, Thailand and Vietnam in S and SE Asia, but not reported in Myanmar^{[1, 11-14]}.

The plants of Actinoschoenus are perennials, characterized by culms scapose, leaf blade present or absent, involucral bracts small, inflorescence capitate with 2 to many spikelets, spikelets with 4-7 distichous deciduous glumes of increasing length, 1 (or 2)- flowered, flowers bisexual, perianth bristles absent, stamens 3, stigmas 3, and nutlets obovoid and 3-sided.

During the recent field survey in Myanmar, we found a plant of Actinoschoenus from Nat Ma Taung (Mt. Victoria), Mindat Township, Chin State. It was determined as A. yunnanensis (C. B. Clarke) Y. C. Tang afterwards. While searching GBIF database (www.gibif.org), we found a specimen collected from Mindat Township, Chin State, Myanmar deposited at BM was identified as A. yunnanensis by T. Koyama. Unfortunately, it was ignored by recent floras and checklists^{[1, 9-14]}. Hence, A. yunnanensis, a species representing a newly recorded genus of flora of Myanmar, was reported and described below.

Actinoschoenus yunnanensis (C. B. Clarke) Y. C. Tang, Abstr. Pap. 30th Anniv. Bot. Soc. China. 130. 1963. —— Fimbristylis yunnanensis C. B. Clarke, J. Linn. Soc., Bot. 36: 247. 1903. Type: Mengzi, Yunnan, China, A. Henry 11150 (holotype: K, isotype: NY). Fig. 1.

(Fig. 1)

Fig. 1 Actinoschoenus yunnanensis (C. B. Clarke) Y. C. Tang. A: Habitat and habit; B: Inflorescences.

Rhizomes creeping. Culms 15-45 cm tall, slender, 0.5-0.7 mm wide. Leaves shorter to longer than culm; blade 1-1.5 mm wide, sparsely hairy, apex acute. Involucral bracts 2 or 3, leaf-like to nearly setaceous, 0.5-2.5 cm, the lowest one longer than inflorescence, hairy. Inflorescence capitate, 0.8-1.3 cm in diameter, with 4-13 spikelets. Spikelets ovoid to narrowly ovoid, 4-6 mm, with 7 or 8 glumes, 1(2)-flowered. Glumes distichous basally, ovate-lanceolate, reddish brown, thickly papery, apically hairy. Stamens 3. Style 3-sided, basally inflated; stigmas 3. Nutlets obovoid, white, 1/3-1/2 as long as subtending glume, obtusely 3-sided.

Distribution: China (Yunnan), India (Assam), Myanmar (Chin State, new record), Thailand, Vietnam.

Ecology: Growing on wooded slopes, 1 300-1 500 m in altitude.

Phenology: Flowering and fruiting from June to July.

Specimens examined: Myanmar. Chin State:Mindat Township, wooded slopes, 21°22′26″ N, 93° 58′57″ E, 1 500 m, 28 June 1956, F. Kindon-Ward 22429 (BM); Mindat Township, Nat Ma Taung (Mt. Victoria), open woods on slopes, 21°11′28″ N, 94°4′ 25″ E, 1 300 m, 4 July 2018, Zhang Shu-ren M0226 (PE).

In Flora of Thailand, D. A. Simpson and T. Koyama treated this species as F. yunnanensis C. B. Clarke, but noted that its placement was uncertain^[11]. According to Goetghebeur, it was only different from other species of Actinoschoenus by having well developed leaf blades, its floral characters agree well with those of the genus, and it could be included in the genus^[5]. Goetghebeur’s opinion was adopted by the following plant taxonomists^{[1, 12-13]}. Although A. yunnanensis have been found in several countries of S and SE Asia, it is rarely found in the field. We had carried out 3 times of field surveys in Myanmar, but only found a small population of the species in Nat Ma Taung (Mt. Victoria). Furthermore, the number of the specimens of the species kept at herbaria are very small. According to GBIF database, there are only 20 specimen collections at different herbaria all over the world.