Malleola micrantha Aver. & Vuong, 2022

Averyanov, Leonid V., Thai, Tran Huy, Truong, Ba Vuong, Nguyen, Van Canh, Nguyen, Tuan Hoang, Maisak, Tatiana V., Nguyen, Khang Sinh & Nguyen, Van Khuong, 2022, New orchids in the flora of Vietnam (Orchidaceae, Aeridinae), Phytotaxa 555 (2), pp. 113-135 : 122-126

Malleola micrantha Aver. & Vuong , sp. nov.

( Figs. 5 , 6 )

Type: — VIETNAM. Lam Dong Province, Dalat City area, 20.04.2019, Truong Ba Vuong , Ngo Quang Dang, BV 407 (holotype VNM, isotype LE01123083 https://en.herbariumle.ru/?t=occ&id=133322) .

Authentic photos and drawings: — VIETNAM. LE 01123084 https://en.herbariumle.ru/?t=occ&id=133330, LE 01123083 https://en.herbariumle.ru/?t=occ&id=133322.

Etymology. The species name refers to its relatively small flowers.

Description. Herb perennial monopodial epiphytic. Stem simple or basally few branched, pendulous and somewhat distally ascending, (1)2–4(5) cm long, terete, (1.4)1.5–2(2.1) mm in diameter, covered by distichous leaf sheaths, with (4)5–7(8) leaves in apical half, in basal part with many wiry, twisted dull gray roots. Leaves subdistichous, sessile, joined, broadly lanceolate to narrowly elliptic, grassy green, (1.2)1.5–2(2.5) cm long, (2.5)3–5(6) mm wide, spreading horizontally, apex obtuse, sometimes shortly unequally bilobed. Inflorescence axillary lax raceme, glabrous, (1.5)2–3.5(4) cm long; peduncle greenish to dull purple, thin, terete, (0.8)1–1.8(2) cm long, naked or with 2–3 distant, sterile triangular, acute bracts, 1–2 mm long and wide; rachis terete, slightly longitudinally angled with (3)4–11(12) flowers distant on (0.5)1–3(3.2) mm; floral bracts, triangular, acute, (0.5)0.6–0.7(0.8) mm long, 0.4–0.5 mm wide. Flowers subsessile, spirally arranged, spreading at right angle to rachis, opening in succession, (3)3.2–3.8(4) mm across, sepals and petals glabrous, pale yellow, each with two obscure reddish-brown strips, lip white with dull purple marks on epichile, column white or little greenish, anther cap light yellow. Pedicel and ovary light green, glabrous, terete, shallowly grooved, (1.8)2–3(3.5) mm long, (0.4)0.5(0.6) mm in diameter. Sepals concave, obtuse to blunt at apex; median sepal ovate, (1.8)2(2.2) mm long, (1.1)1.2(1.3) wide (being flattened), cymbiform, dorsally gibbous and hooded; lateral sepals broadly obovate, slightly oblique, (2.1)2.2(2.3) mm long, (1.7)1.8(1.9) wide, almost round at apex. Petals concave, obtuse to blunt at apex, ovate, (1.7)1.8–2(2.1) mm long, (0.9)1(1.1) mm wide. Lip simple or obscurely 3-lobed, spurred, (3.8)4–4.2(4.4) mm long from apex of the lip to apex of spur, firmly fused by lateral sides with column base, with spur lying almost parallel to ovary; epichile 1.5–1.6 mm long and wide, entire triangular or with obscure roundish side-lobes, at apex attenuate to small straight or down recurved acute seta 0.3–0.4 mm long, disk with 2 short parallel low keels; spur glossy white, shortly cylindrical, with no constriction, (2)2.2–2.6(2.8) mm long, (0.8)1(1.2) mm in diameter, oblique conical and round at apex. Column footless, erect, stout, 1–1.2 mm tall and wide, at front with 2 large forward directed conoid papillose bosses 0.7–0.8 mm long, 0.6–0.7 mm in diameter at the base; rostellum very small, placed between bosses; stigma large, concave, circular. Anther cap large, as tall and broad as column, half-globular, 1-2 mm in diameter, with narrowly triangular, down directed beak. Pollinia 2, globular, about 0.3 mm in diameter (0.15–0.2 mm when dry), with small groove on outer surface; stipe linear, translucent, longitudinally conduplicate, bent in the middle and suddenly much widening into broad plate with incurved lateral margins, 1.2–1.4 mm long, 0.8–0.9 mm wide in widest part; viscidium very small, ovate, about 0.1 mm long. Fruits unknown.

Habitat, phenology and conservation status. Miniature monopodial canopy epiphyte. Primary evergreen broadleaved submontane forests. Fl. April. Very rare. Estimated IUCN Red List status – CR.

Distribution. Southern Vietnam (Lam Dong province). Endemic.

Notes. Like Malleola luongii Averyanov & V.C.Nguyen in Averyanov et al. (2018: 130) recently discovered in Vietnam, the new species belongs to the so-called Malleola dentifera – vietnamensis complex, taxa of which occur from Indochina and Peninsular Malaysia to the Greater Sunda Islands ( O’Byrne, 2017). Our plant is closest to the type subspecies of M. vietnamensis Guillaumin (1964: 268) , including M. dentifera J.J. Smith (1927: 191) as a synonym ( O’Byrne 2017), in a general appearance and color scheme of the flower. It differs from M. vietnamensis var. vietnamensis discovered plant differs in the distinctly shorter stem 1–5 cm long (vs. stem normally 10–45 cm long), leaves 1.5–2.5 cm long (vs. leaves normally 3.2–10 cm long), inflorescence lax flowered, flowers 3–4 mm across (vs. inflorescence subdense, flowers 5.5–8.5 mm across), lip simple or with obscure roundish side-lobes (vs. lip distinctly 3-lobed, side-lobes triangular acute forming forward directed teeth), lip disc with 2 short low keels, lip apex with small narrowly triangular straight or down curved seta (vs. disc with no ornamentation, lip apex attenuate to linear revolute or helicoid curved processus), spur shortly cylindric without constriction, 2–2.8 mm long (vs. spur commonly dorso-ventrally flattened in apical half, often constricted in apical half, 3.7–7 mm long), column at front with conical swellings (column with hemispheric swellings), pollinarium stipe 1.2–1.4 mm long (vs. pollinarium stipe 1.9–2 mm long), pollinia 0.3 mm in diameter to 0.2 mm in diameter when dry (vs. pollinia 0.4–0.9 mm in diameter).

Only few specimens of the new species were found in densely populated area where most lands has been converted into agricultural plantations.Area of Occupancy (AOO) is estimated as 4 km 2, and as the result due to available data and observations the species should be preliminarily estimated as Critically Endangered – CR B2ab(iii) ( IUCN 2019).

It is noteworthy that like its allies, the new species exhibits certain apomorphic characters such as prominently inflated lateral stelidia and apically broadening pollinarium stipe. These features along with the subulate or caudate, downward revolute lip apex, lack of distinct calli in spur and almost entire pollinia set this group apart from the related genus Robiquetia Gaudichaud-Beaupré in Freycinet (1829: 426), with which Malleola has been merged on the basis of molecular data ( Kocyan and Schuiteman, 2014).

Figures

FIGURE 5. Malleola micrantha. A. Flowering plant. B. Intact flower, half side view.C. Flower, side view, lateral sepal and petal reflexed. D. Flower, frontal view. E. Separated lip, side view. F. Lip, sagittal section. G. Separated lip, view from above. H. Lip, tangential section, upper part removed. I. Anther cap, view from above and from below. J. Pollinarium, abaxial side. K. Pollinarium, adaxial side. L. Pollinarium stipe, adaxial side, pollinia removed. All drawn from the type specimen (BV 407) by L. Averyanov and T. Maisak.

FIGURE 6. Malleola micrantha. A. Flowering plant, all leaves from adaxial side. B. Apical half of flowering plant, all leaves from abaxial side. C. Inflorescence. D. Leaves from adaxial and from abaxial side. E. Leaf apex, adaxial side. F. Instant flowers from different sides. G. Flattened sepals and petals. H. Pedicel, ovary, column and lip, side view. I. Separated lip, view from above. J. Lip, sagittal section. K. Pedicel, ovary and column, frontal and half side views. L. Anther cap, half side view and view from below. M. Pollinarium, view from different sides. All photos by Truong Ba Vuong from the type specimen (BV 407), photo correction and design by L. Averyanov and T. Maisak.