The review of Bulbophyllum section Tripudianthes (Orchidaceae) in the flora of Vietnam with the description of new species, B. viridipallidum Author Nguyen, Van Canh 0000-0001-9578-0342 Institute of Applied Technology, Thu Dau Mot University No. 06, Tran Van On Street, Phu Hoa Ward, The Dau Mot City, Binh Duong Province, Vietnam. & nguyenvancanh @ gmail. com; https: // orcid. org / 0000 - 0001 - 9578 - 0342 nguyenvancanh@gmail.com Author Averyanov, Leonid V. 0000-0001-8031-2925 Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov Street 2, 197376, St. Petersburg, Russia. & av _ leonid @ mail. ru; https: // orcid. org / 0000 - 0001 - 8031 - 2925 av_leonid@mail.ru Author Maisak, Tatiana V. 0000-0001-5919-6755 Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov Street 2, 197376, St. Petersburg, Russia. & tmaisak @ mail. ru; https: // orcid. org / 0000 - 0001 - 5919 - 6755 tmaisak@mail.ru Author Nguyen, Thi Lien Thuong 0000-0001-8219-0431 Institute of Applied Technology, Thu Dau Mot University No. 06, Tran Van On Street, Phu Hoa Ward, The Dau Mot City, Binh Duong Province, Vietnam. & thuongntl @ tdmu. edu. vn; https: // orcid. org / 0000 - 0001 - 8219 - 0431 thuongntl@tdmu.edu.vn Author Nguyen, Van Khuong 0000-0002-1264-5178 Institute of Applied Technology, Thu Dau Mot University No. 06, Tran Van On Street, Phu Hoa Ward, The Dau Mot City, Binh Duong Province, Vietnam. & nguyenkhuongbanme @ gmail. com; https: // orcid. org / 0000 - 0002 - 1264 - 5178 nguyenkhuongbanme@gmail.com Author Pham, Thi Thanh Dat 0000-0003-0585-1050 Institute of Applied Technology, Thu Dau Mot University No. 06, Tran Van On Street, Phu Hoa Ward, The Dau Mot City, Binh Duong Province, Vietnam. & phamthithanhdat @ gmail. com; https: // orcid. org / 0000 - 0003 - 0585 - 1050 phamthithanhdat@gmail.com Author Nguyen, Danh Duc 0000-0002-3331-8571 Institute of Applied Technology, Thu Dau Mot University No. 06, Tran Van On Street, Phu Hoa Ward, The Dau Mot City, Binh Duong Province, Vietnam. & nguyendanhduc @ tdmu. edu. vn; https: // orcid. org / 0000 - 0002 - 3331 - 8571 nguyendanhduc@tdmu.edu.vn Author Dang, Van Son 0000-0001-8681-4141 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay District, Hanoi, Vietnam. & Institute of Tropical Biology Vietnam Academy of Science and Technology, 85 Tran Quoc Toan, District 3, Ho Chi Minh City, Vietnam. Number 199 / 128 the connect 9 Kaset-Navamin rd. Klong Kum, Bueng Kum, Bangkok 10240. & dvsonitb @ gmail. com; https: // orcid. org / 0000 - 0001 - 8681 - 4141 dvsonitb@gmail.com Author Aromyen, Warapong 0009-0004-8510-8981 warapongnoom @ gmail. com; https: // orcid. org / 0009 - 0004 - 8510 - 8981 warapongnoom@gmail.com Author Truong, Ba Vuong 0000-0003-3452-8455 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay District, Hanoi, Vietnam. & Institute of Tropical Biology Vietnam Academy of Science and Technology, 85 Tran Quoc Toan, District 3, Ho Chi Minh City, Vietnam. Number 199 / 128 the connect 9 Kaset-Navamin rd. Klong Kum, Bueng Kum, Bangkok 10240. & bavuong 2019 @ yahoo. com; https: // orcid. org / 0000 - 0003 - 3452 - 8455 bavuong2019@yahoo.com text Phytotaxa 2023 2023-05-19 598 1 59 68 http://dx.doi.org/10.11646/phytotaxa.598.1.4 journal article 10.11646/phytotaxa.598.1.4 1179-3163 7958804 3. B. viridipallidum Vuong, Aver. & V.C.Nguyen sp. nov. ( Fig. 2 ). Type :— VIETNAM . Kon Tum Province , Dak Ha District , Dak Psi Commune , Dak Trua Forest , epiphyte on tall trees, 16 February 2023 , Truong Ba Vuong, BV 1688 ( holotype VNM00043087 !) . Etymology: —the specific epithet refers to the pale greenish yellow lateral sepals, a character common with related species. Description:—Herb perennial, epiphytic. Pseudobulbs densely clustering, ovoid to broadly ovoid, sometime slightly compress, 7–16 mm long, 5–17 mm in diameter, 2-leaved. Leaves deciduous, plant leafless at anthesis. Inflorescence from base of pseudobulbs; peduncle greenish-yellow, 39 – 40 cm long, at base with 2 scarious, brownish overlapping tubular bracts, above with 2 similar bracts; rachis pendulous, 3.5 – 4 cm long, bearing 6 simultaneously opening flowers; floral bract triangular, brown 1.7–2 mm long, acute; pedicel and ovary 2.5–3 mm long, pedicel terete shorter than conoid ovary. Flowers odorless, lateral sepals pale greenish yellow; median sepal and petals pale reddish brown, lip white speckled with pink or pink purple, callus yellow, with many pink dots at apex dark purple. Median sepal ovate to broadly ovate, ca. 5.5 mm long, ca. 3 mm wide, acuminate to attenuate, adaxially in middle with 2 prominent keels, in apical half sparsely hairy with stiff hairs. Lateral sepals obliquely oblong lanceolate, ca. 4 cm long, ca. 0.3 cm wide, acute, twisted at base, lower margin free at base, connate to the tip, adaxial surface sparsely hairy with short stiff hairs. Petals obliquely triangular, glabrous, 4–4.5 mm long, 1–1.5 mm wide, margin fimbriate, acuminate to attenuate. Lip simple, oblong in outline, 3–3.2 mm long, 1–1.5 mm wide, movably adnate to column foot by small ligament, apex rounded; margins in basal half erect, finely papillose, apical half fimbriate along the margin; adaxial surface at base with 2 rounded longitudinal calli fused distally into a single prominent central longitudinal keel inflated at the lip apex turn into prominent half-ovoid callus; abaxial sparely pillose. Column ca. 1.5 mm long, at front with inconspicuous rounded wings; column foot 2–2.5 cm long, forward directed, straight; stelidia subulate, ca. 1 mm long, slightly curved; stigma half circular, concave, ca. 1 mm across; rostelum non protruding; anther cap helmet shaped, ca. 1 mm long, apex with a gibbose densely papillose inflation; pollinia 4, bright yellow, half ovoid, inner smaller than outer. Fruits not seen. FIGURE 1. Bulbophyllum wallichii Reichenbach. A. Flowering plant. B. Pseudobulb with leaves. C. Intact inflorescence. D. Portion of inflorescence. E. Floral bract. F. Base of intact flower. G. Median sepal, abaxial and adaxial side. H. Lateral sepals, abaxial and adaxial side. I. Petals, abaxial and adaxial side. J. Lip, view from different sides. K. Pedicel, ovary, column and lip, side view. L. Pedicel, ovary, column and column foot, side view. M. Pedicel, ovary and column view from above. N. Column apex, frontal view. O. Stelidia on the column apex. P. Anther cap, view from above and from below. Q. Pollinaria, view from different sides. All photos by Truong Ba Vuong from BV 1483 , photo correction and design by L. Averyanov and T. Maisak FIGURE 2. Bulbophyllum viridipallidium Vuong, Aver. & V. C. Nguyen , sp. nov. A. Flowering plant. B. intact inflorescence. C. Portion of inflorescence. D. Floral bract. E. Base of flower, with median sepal, view from above. F. Intact flowers, view from above and from below. G. Median sepal, abaxial side, adaxial side, and side view. H. Lateral sepals, abaxial and adaxial side. I. Petals, abaxial and adaxial side. J. Lip, view from different sides. K. Ovary, column and lip, side view. L. Ovary, column and column foot, side view. M. Column apex, side and frontal view. N. Anther cap, view from different sides. O. Pollinaria, view from different sides. All photos by Truong Ba Vuong from type specimen BV 1688 , photo correction and design by L. Averyanov and T. Maisak. FIGURE 3. Flower and dorsal sepal comparison between: A & B. Bulbophyllum khaoyaiense . C. & D . B. kanburiense . E. & F. B. refractum . G. & H. B. tripudians (photo by Warapong Aromyen from Thailand). FIGURE 4. Bulbophyllum refractum (Zollinger) Reichenbach. A. Leafy plant. B. Flowering plant. C. Inflorescence detached. D. Flower, view from above and from below. E. Median sepal, abaxial and adaxial side. F. Lateral sepals, adaxial and abaxial side. G. Margin of lateral sepals. H. Petals, abaxial and adaxial side. I. Lip, views from various angles. J. Flower, side view, sepals removed. K. Pedicel, ovary, and column, side view. L. Apex of column with stelidia, side view. M. Apex of column, frontal view. N. Anther cap, view from above and from below. O. Pollinaria, frontal and rear views. All photos by Truong Ba Vuong from BV 1046 , photo correction and design by L. Averyanov and T. Maisak. Habitat and phenology: —Epiphyte on tall trees in evergreen broad-leaved forest. Flowering observed during February. Distribution: — VIETNAM ( Kon Tum Province , Dak Ha District). Endemic. Proposed conservation status :—According to currently available data, the new species is very rare and found only from one location. More field studies are required for preparing its conservation assessment. In view of gaps in data and in accordance with IUCN criteria ( IUCN, 2022 ), the species should be assessed as Data Deficient (DD). Notes :—The new species in its entire median sepal is similar B. kanburiense and B. khaoyaiense . It also similar with B. wallichii in two prominent calli placed on the lip base. The dorsal sepal and flower comparison is presented on Fig. 3 . The morphological differences of the new species and morphologically similar species are presented in the table. TABLE. The comparison of morphological characters of B. viridipallidum , B. kanburiense , B. khaoyaiense , and B. wallichii

B. viridipallidum	B. kanburiense	B. khaoyaiense	B. wallichii
Median sepal length, shape, and margin	ca. 5.5 mm long, ovate to broadly ovate, acuminate to attenuate, margin glabrous, sparsely hairy in apical half	ca. 5.5 mm long, ovate, acute, with few hairs at apical half	ca. 3.8 mm long, triangular, with few teeth on margin	ca. 10 mm long, narrowly triangular, attenuate, margin fimbriate, surface sparsely hairy
Lateral sepal length and margin	ca. 4 cm long, sparsely hairy with short hairs	ca. 2.5 cm long, glabrous	ca. 1.9 cm long, glabrous	ca. 4.5 cm long, glabrous
Petal shape and indumentum	triangular, margin fimbriate, surface glabrous	triangular, margin fimbriate, surface hairy at apical half	triangular, margin fringed, surface few stiff hairs	narrowly triangular, margin fimbriate, surface few stiff hairs
Lip indumentum	apical half fimbriate along the margin, abaxial surface with sparely pillose	apical half densely ciliate	abaxial surface with many tufted hairs	apex densely papillose and margin and abaxial apical half finely papillose and sparely pillose
Lip ornamentation	adaxial surface at base with 2 rounded calli fused distally into a single central prominent longitudinal keel inflated at the lip apex into prominent half-ovoid callus	no ornamentation	no ornamentation	2 rounded calli at the base fused into single callus covered almost the lip surface, with swollen half ovoid callus at apex
Color of lateral sepals	pale greenish yellow	orange yellow	yellow	orange

Data of B. wallichii based on BV 1484 ( VNM 00043086), BV 1483 ( LE 01123508 & LE 01169312); data of B. kanburiense based on Seidenfaden (1970: 344) ; data of B. khaoyaiense based on Seidenfaden & Smitinand (1965: 795) and Seidenfaden (1970: 342) .