Thismia sect. Labiothismia Smith (1927: 222)

Type species:— Thismia labiata Smith (1927: 220) .

Synonym:— Thismia sect. Glaziocharis Kumar et al. (2017: 233), nom. illeg., non (Taub. ex Warm.) Hatusima (1976). Type species:— Thismia abei (Akasawa) Hatusima (1976: 7) .

Description:—Herbs up to 6(–10) cm tall. Underground part represented by creeping vermiform roots. Flowers terminal and solitary (sometimes in monochasium in T. thaithongiana), surrounded by involucre of usually 3 bracts. Flowers actinomorphic or zygomorphic (zygomorphy due to bent hypanthium, or bilabiate-looking annulus and perianth, or manner of tepal fusion), variously coloured. Hypanthium inner surface without transverse bars, usually smooth. Annulus of various shape, more or less ring-like. Outer tepals unappendaged or with appendages ranging from short protuberance-like to long and filiform. Inner tepals with appendages ranging from short protuberance-like to long and filiform (unappendaged in T. americana). Inner tepals postgenitally fused into a mitre (reports of tepals overlapping to form a loose dome need verification: Nuraliev et al. (2024)). Mitre often with imbricate (or contort) tepal aestivation. Stamens laminar, with long supraconnectives, fused postgenitally into a stamen tube (reports of free stamens need verification: Nuraliev et al. (2024)). Supraconnective usually distally bent outwards, without skirt-like or wing-like appendage, with entire apex (without teeth). Interstaminal glands absent. Thecae sometimes surrounded by rows of glandular hairs. Placentas parietal, usually becoming column-like by detachment from ovary wall; styles terminating stylar column, united into a pyramidal structure or free. At fruit maturation, hypanthium abscises circumscissily. Fruit cup-shaped (a pyxidium), dehiscing apically by withering; pedicel sometimes elongating greatly during fruit maturation.

Taxonomic notes:— Thismia sect. Labiothismia is uniform in a set of morphological traits that also makes the section distinct from the rest of the genus. These traits are: underground organs represented by vermiform roots; absence of transverse bars inside the hypanthium; inner tepals forming a mitre or a loose dome (possibly, exclusively a mitre: see discussion by Nuraliev et al. 2024); presence of appendages of the inner tepals that are usually longer than 1 mm (but the inner tepals are unappendaged in T. americana Pfeiffer (1914: 123)); absence of a wing-like appendage of supraconnective; absence of interstaminal glands.

Distribution: — India (Western Ghats), Japan, China (Yunnan), Taiwan, Thailand, Laos, Vietnam, Peninsular Malaysia, Indonesia (Sumatra), USA (Illinois).

All of the 14 species of the section, except for T. abei, are known to be narrow endemics restricted to the type localities or their close vicinities (Fig. 1).