Tên Khoa học: Cephalanthera exigua Seidenf.
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Description based on plants from Vietnam: Stem erect, slender, 5—10 cm tall, the lower part covered by 3—5 papyraceous sheaths 0.5—1 cm long, upper part with 1—3 distant tiny floral bracts. Floral bracts narrowly ovate, acute to shortly acuminate, 0.5—1 cm long, same length as the ovary. Flowers 1—2(3), not widely opening, campanulate, 1.5 cm across. Sepals subsimilar, narrowly ovate, acuminate to shortly apiculate, 11—12 mm long, 4—5 mm wide, lateral sepals slightly broader, oblique at the base. Petals narrowly ovate, little shorter, obtuse. Lip 10—11 mm long, inside very papillose, distinctly separated into hypochile and epichile. Hypochile cup¬shaped, with oblong, falcate, erect side lobes 6—7 mm long. Epichile cordate, 7—8 mm long and wide, 3-lobed; lateral lobes half circular, shallowly crenulate; median lobe triangularly ovate, reflexed downwards, roughly papillate, grooved, at least two times smaller than the lateral ones. Lip with 3 low keels running from the base almost to the apex, lamellately thickened at the basal half of epichile. Column narrow, slender, straight, 5—7 mm tall, with erect oblong anther 3 mm long. Stigma apical, obscurely triangular, concave.
Distribution: Laos, Thailand, Vietnam (Fig. 3).
Ecology: In Vietnam it grows in primary broad-leaved evergreen shady forests on mountain slopes composed by silicate rocks. 1000 m. Fl. April—May. The area inhabited by C. exigua is fairly rich in mycoheterotrophic plants. Particularly, Vietorchis furcata Aver. & Nuraliev, Orchidaceae (Averyanov et al. 2013), Epipogium roseum D. Don, Orchidaceae, and Thismia mucronata Nuraliev, Thismiaceae (Nuraliev et al. 2014) were reported to occur at a distance of 3 km and less from the population of C. exigua.
Conservation status: Cephalanthera exigua in Indochina is defined as Critically Endangered [CR B2ab(iii)] based on its small geographic range (IUCN 2014).