Biermannia averyanovii var. micrantha Aver. & K.S.Nguyen, var. nov.

(Fig. 8)

Diagnosis: — Biermannia averyanovii var. micrantha differs from the type of B. averyanovii in the twice smaller flowers with sepals less than 3 mm long, floral bracts ovate triangular, little longer than wide, pedicel and ovary less than 1.5 mm long, and lip median lobe laterally flattened, almost straight, less than 0.8 mm long.

Type: — VIETNAM. Son La Province: Thuan Chau District, Phong Lai Commune, Phieng Long Village, foots of Pha Din Pass area, remnants of primary evergreen broad-leaved forests on limestone mountains at elevation of 800–1000 m a.s.l., 5 July 2023, K. S. Nguyen & T. V. Lo, AL 2233b (holotype LE: LE 01276689 https://en.herbariumle.ru/?t=occ&id=235153, photos from plant used for the preparation of type specimens LE 01255179 https://en.herbariumle.ru/?t=occ&id=234689, drawing LE 01255180 https:// en.herbariumle.ru/?t=occ&id=234690).

Description:—Herb monopodial, miniature, epiphytic, glabrous. Stem (0.4)0.6–1.2(1.4) cm long, completely covered by distichous leaf sheaths, slightly flattened, with many pale green wiry roots clustered near stem base. Leaves (5)6–8(10), sessile, jointed, obliquely broadly lanceolate, (2)2.5–4(4.5) cm long, (4.5)5–8(10) mm wide, apex with two subacute oblique unequal lobes. Inflorescence, axillary, subdense, head-like raceme, erect, glabrous; peduncle straight, terete, (4.5)5–6(7) mm long, about 1 mm in diameter, with (1)2–3(4) close sterile triangular ovate, shortly acuminate bracts, (0.8)1–1.2(1.4) mm long, 0.6–0.8 mm wide; rachis somewhat inflated, (2.5)3–5(5.5) mm long, (1)1.2–1.6(1.8) mm in diameter, twice wider than peduncle, with many spirally arranged triangular floral bracts; floral bracts close to each other, triangular, sharp. persistent, (1.4)1.6–1.8(2) mm long, 0.8–1 mm wide, with acute, somewhat recurved apex; 1–4(5) flowers blooming simultaneously; inflorescence developing for a long time and thus flowers occupy its apical half. Flowers opening during a few morning hours, shortly fugacious, resupinate. Pedicel and ovary light green, glabrous or with few scattered scurfy hairs, terete, shallowly 6-grooved, suberect, straight or slightly recurved, (1.1)1.2–1.4(1.5) mm long, 0.3–0.35 mm in diameter. Sepals free, subequal, broadly lanceolate to narrowly ovate, acuminate, tapering from broad base to the apex, straight, (2.7)2.8–2.9(3) mm long, (0.7)0.8(0.9) mm wide near the base, uniformly light yellowish, slightly carinate outside. Petals narrowly triangular, acuminate, tapering from broad base to the apex, straight, (2.3)2.4–2.6(2.7) mm long, 0.7–0.8 mm wide, uniformly light yellowish. Lip simple, triangular ovate in outline, obscurely trilobed, with fleshy center and thin side lobes, almost straight, movably attached to the apex of column foot, lying almost parallel to column, (1.7)1.8–2(2.1) mm long, wide, 1.3–1.4 mm wide (when flattened), pale yellowish; side lobes half-circular, erect, very thin, (0.9)1(1.1) mm broad, 0.3–0.4 mm tall, entire or finely erose along the margin; median lobe fleshy, narrowly conoid, slightly laterally flattened, acuminate, straight, forward directed, 0.7–0.8 mm long; disc without ornamentation. Column erect, stout, (0.8)1(1.2) mm tall, 0.6–0.7 mm wide; stigma ovate to almost circular, concave; column foot free, forward directed, little shorter than column. Operculum cap-shaped, about 0.5 mm in diameter, with straight margin without beak. Pollinia 2, globular, 0.2–2.2 mm in diameter, entire or with a hardly visible cavity; stipe oblong, about 0.1 mm long, viscidium half this size, ovate. Fruit not seen.

Etymology:— The varietal epithet refers to the small size of flower particularly to this species.

Ecology and phenology:— Monopodial canopy epiphyte. Primary evergreen broad-leaved submontane forests on karstic limestone at elevations of 800–1000 m a.s.l. Flowers in June–July.

Distribution:— Endemic to Son La Province (Thuan Chau District) thus far.

Conservation status:— Biermannia averyanovii var. micrantha is presently known from a single site with one documented population. Nothing much is known about the ecology of this variety. Accordingly, it can be assessed as Data Deficient (DD) following formal criteria proposed by the IUCN (2024).