Cleisostoma Blume (1825: 362)

Kumar, Pankaj, Gale, Stephan W., Phaxaysombath, Thatsaphone & Fischer, Gunter A., 2018, Cleisostoma schoenorchaefolium (Orchidaceae: Vandeae: Aeridinae), a new species from Lao PDR, Phytotaxa 374 (2), pp. 155-161 : 155-156

Cleisostoma Blume (1825: 362)

Type species:— Cleisostoma sagittatum Blume (1825: 363)

Seidenfaden (1975: 7), Averyanov et al. (2015: 108), O’Byrne (2009: 77, 2010: 89), Wood (2014: 161), Ponert et al. (2016: e0150631). Echioglossum Blume (1825: 364) .

Sarcanthus Lindley (1826 : t. 39B), nom. illeg.

Carteretia Richard (1834: 10 . t. 4).

Garayanthus Szlachetko (1995: 136) .

Raciborskanthos Szlachetko (1995: 135) .

Blumeorchis Szlachetko (2003: 68) .

Ormerodia Szlachetko (2003: 68) .

Monopodial epiphytic or lithophytic herbs. Stem usually branched, erect or pendent, creeping. Leaves flat, terete or semi-terete, often conduplicate at base. Inflorescences lateral, short to long, racemose or paniculate, bearing one to many flowers with floral parts shorter than the pedicel and ovary. Petals and sepals similar although sepals usually narrower, spreading, free. Labellum trilobed, basally attached to the base of the column or a distinct column foot, immobile, spurred; side lobes erect to porrect, triangular; midlobe deltoid or sagittate; spur cylindrical, conical or saccate, with a callus projecting from the inner back wall, sometimes with another callus on the inner front wall close to the entrance, sometimes with a median septum inside. Column short, with or without distinct foot, with or without wings; anther cap terminal, operculate. Pollinia 4, grouped into two unequal masses, waxy, connected by a stipe; stipe and viscidium morphology variable.

The genus comprises around 110 species distributed from tropical and subtropical Asia to the western Pacific (Pridgeon et al. 2014, Averyanov et al. 2015, Govaerts et al. 2018). Of these, 51 species are found in the Indo-Burma biodiversity hotspot ( Li et al. 2018), including 12 species known to occur in Laos. Wood (2014) recognised seven sections within the genus, to which two new sections have recently been added ( Averyanov et al. 2015).

The new species conforms to be generic concept in possessing an immotile, trilobed labellum that is attached directly to the base of the column, an inverted y-shaped callus on the back wall of the spur, a tooth-shaped, truncate rostellum and four pollinia grouped in two semi-globular masses placed on either side of the stipe. However, it differs markedly from other members of the genus in certain vegetative (semi-terete leaves with a subulate apex) and floral (complex stipe structure, two-chambered spur) attributes, precluding its satisfactory placement in any one of the existing sections. Hence, a new section, sect. Teretisculum , is described to accommodate it. A key is provided to all ten sections.