Hoya honglenae Aver., Vuong, Bao & V.C.Nguyen, 2023

Nguyen, Van Canh, Averyanov, Leonid V., Nguyen, Quoc Bao, Dang, Van Son, Nguyen, Van Khuong, Maisak, Tatiana V. & Truong, Ba Vuong, 2023, A new species, Hoya honglenae and the first report of H. acuminata and H. phuwuaensis (Apocynaceae, Asclepiadoideae) in the flora of Vietnam, Phytotaxa 632 (1), pp. 60-68 : 62-65

Hoya honglenae Aver., Vuong, Bao & V.C.Nguyen , sp. nov.

H. sect. Peltostemma Schlechter (1916: 14)

( Fig. 2 ).

Diagnosis:—The new species differs from the morphologically closest Hoya phuwuaensis in the usually entire, straight leaf margin rarely slightly undulate (vs. leaf margin wrinkled and somewhat revolute), leaf blade sparsely white speckled adaxially and dirty purple speckled abaxially (vs. leaves with large white blotches all over the adaxial surface and uniform light green abaxially), corolla yellow to pale yellow orange, 6–7 mm in diameter (vs. corolla white, 8–12 mm in diameter), oblong-conoid, obtuse, distinctly up-curved outer angle of corona lobes (vs. outer angle narrowly ovoid, round at apex, not up-cured), and oblong, truncate to obtuse anther appendages 1–1.2 mm long (vs. anther appendages triangular, acute, 0.8–1 mm long).

Type: — VIETNAM. Kien Giang Province: Phu Quoc Island, herbarium prepared from plants cultivated in Buon Ma Thuot Town (Dak Lak Province of southern Vietnam) in June 2021, by Nguyen Van Canh, AL 1399 (LE 01169050 https://en.herbariumle.ru/?t=occ&id=140570, authentic photos—LE 01124053 https://en.herbariumle.ru/?t=occ&id=165927) .

Paratypes:— VIETNAM. Kien Giang Province: Phu Quoc Island, herbarium prepared from cultivated plants in June 2021, by Nguyen Van Canh, AL 1400 ( LE 01169051 https://en.herbariumle.ru/?t=occ&id=140569). VIETNAM. Kien Giang Province: Phu Quoc Island, lowland forest around Cua Duong Commune, epiphyte, 11 December 2022, Truong Ba Vuong, Nguyen van Canh & Nguyen Quoc Bao, BV 1668 ( VNM 00043090).

Etymology: —The species is named after Mrs. Nguyen Thi Hong Len, who found it in nature and kindly shared the specimens to study.

Description: —Slender creeping epiphytic herbaceous vine 3–4 m long with white to yellowish white latex in all vegetative parts. Stem terete, 3–4 mm in diameter, greenish brown to gray, verrucose, with stiff sparse hairs; internodes 3.5–10 cm long. Leaves shortly petiolate; petiole stout, black, 5–6 mm long, 3 mm in diameter, densely bristle; leaf blade thick, rigid, coriaceous, narrowly ovate to elliptic, acute, 5.5–6 cm long, 2.5–3 cm wide, almost glabrous, or with sparse, very short strigose hairs, base broadly cuneate to almost round, nerves inconspicuous on both sides, margin entire or slightly undulate, adaxial surface dark grassy green with irregular white and dirty purple brownish marks, abaxial surface pale green with many dirty purple violet speckles. Inflorescence extra-axillary, pendulous, umbelliform raceme, slightly concave in outline, normally bearing 8–20(22) flowers; peduncle terete, slender, down directed, 3.5–4.5 cm long, 0.9–1.2 mm in diameter, straight to slightly curved, scabrous; rachis perennial, fleshy, terete, gray brown, 0.8–1.4 cm long, 3–3.5 mm in diameter, bearing flowers at apex; flower buds broadly conoid, pentagonal; flowers widely opening, almost flat. Pedicels white, sometimes with a purple tint, about 0.8 mm in diameter, in peripheral flowers 1–1.2 cm long, at the center of inflorescence 7–9 mm long, somewhat verruculose. Calyx persistent, deeply 5-lobed; lobes pale pinkish, narrowly triangular ovate, about 1 mm long, 0.5 mm wide, acute to obtuse, adaxial surface glabrous, abaxial surface scabrous. Corolla discoid, with 5 broadly triangular lobes, yellow to pale yellow orange, 6–7 mm in diameter; adaxial surface densely pubescent with long white stiffy hairs; abaxial surface glabrous; connate part 1–1.2 mm long; lobes distally revolute, 3–4 mm long, apex triangular acute. Corona purple to dark purple, 5 lobed, 3–4 mm in diameter; outer angle of corona lobe oblong-conoid, 1.4–1.6 mm long, distally up-cured, with obtuse apex, upper surface convex, lower sulcate; inner angle of corona lobe erect, narrowly conoid, acute, 1.1– 1.3 mm tall, much higher than outer angles. Anther appendages yellow with white apical part, oblong to triangular oblong, 1–1.2 mm long, 0.2–0.3 mm broad, erect, truncate, much longer than apex of inner corona angles, covering the stigma head. Pollinarium about 0.4 mm long; pollinia light yellow, obliquely oblong, narrowly winged, 0.32–0.34 mm long, apex of pollinia truncate, margins pellucid; caudicles stout, short, hyaline, with broad deltoid wing, light pale yellow; translators, pale yellow, obscurely triangular; corpusculum brown, ovate, obtriangular, laterally compressed. Pistil white to light pink, about 1 mm long, of 2 separate, glabrous, wine bottle shaped ovaries. Stigma head white, broadly conoid, about 0.8–0.9 mm tall and wide. Fruits and seeds not seen.

Habitat and phenology: —Dry lowland evergreen broad-leaved forests, commonly under canopies of tall trees at elevation 50–150 m a.s.l. Flowers in June.

Distribution: — Vietnam, Kien Giang Province (Phu Quoc Island). Endemic.

Conservation status: —The described plant was observed as an uncommon epiphytic vine in a single location. This species’ habitat has remained untouched until now, but the plant may face commercial collecting in the future. Additionally, a small number of mature plants in a single population with a very small area of occurrence and occupation identify preliminary species status as Globally Critically Endangered (Globally CR), following the formal criteria of the IUCN (2022) as follows: B1a,b(v)+2a,b(v); C1+2(i,ii); D1—the area of occurrence <100 km ² (B1) and the area of occupancy <10 km ² (B2), with 1 known population (a);—the number of mature individuals <250, estimated or projected continuing decline in 25% in 3 years or 1 generation (C1), and estimated, projected or inferred continuing decline when the number of mature individuals in each subpopulation (C2(i)) ≤ 50 and % of mature individuals in one subpopulation = 90–100% (C2(ii));—the number of mature individuals <50 (D).

Note:—Among morphologically similar Indochinese species of the section Peltostemma , such as H. phuwuaensis Kidyoo (2016: 218) , H. caudata Hooker (1883: 60) , and H. soidaoensis Kidyoo (2013: 45) , our species is most close to H. phuwuaensis . Segregating morphological characters of related species are presented in Table 1 .

Data on morphological characters of Hoya phuwuaensis , H. caudata , and H. soidaoensis are compiled from the literature sources ( Kidyoo 2013, 2016, Middleton & Rodda 2019).

Figures

FIGURE 2. Hoya honglenae Aver., Vuong, Bao & V.C.Nguyen. A, B. Flattened portion of plant with leaves (A) and flowers (B). C. Portion of the stem. D. Petiole. E. Latex on the stem cut. F. Inflorescence with opening flower buds. G. Inflorescence with opening flowers, view from above. H. Inflorescence with fully open flowers. I. Intact fully open flowers, frontal view. J. Separated flowers and pedicel, frontal view and view from back. K. Pedicel and calyx, side view. L. Pedicel surface. M. Flower, half side view. N. Corolla, adaxial and abaxial side. O. Corona, views from different sides. P. Flower, sagittal section. Q. Pollinaria, view from different sides. R. Calyx with exposed pistil. S. Ovaries. All photos made from plant used for the preparation of the type herbarium specimen AL 1399 by Nguyen Van Canh and Truong Ba Vuong, photo correction and design by L. Averyanov and T. Maisak.