Scientific name: Hoya lockii The P.V. et Aver.English name: Vietnamese name: Cẩm cù lộcOther name:
Suffruticulus epiphyticus caulis erectis pubescentibus 40 – 80 cm altis. Inflorescentia umbellata 8 – 25-flores. Flores odorata, candida, 2 cm in diametro. Sepala lanceolata, 7 – 10 mm longa, 1 – 1.5 mm lata, extus tomentosa. Petala ovata, 10 mm longa, 7 mm lata. Lobi corollae 4.5 – 5 mm longi, 3.5 – 4 mm lati, basi semicirculares, apice abrupte mucronati.
Epiphytic undershrub with white latex. Plant pubescent throughout except fo r on the leaf blade and the corona. Stems erect, 40 – 80 cm long, dark green, with dirty-purple marks towards the base, terete, to 3 mm in diam., with slightly swollen nodes, internodes to 4 cm long, nearly straight. Leaves decussate. Petiole straight, 1–1.3 cm long, 2-3 mm in diam., terete, canaliculate, dark green with dirty purple spots. Leaf blade elliptic or narrowly obovate, 7.5 – 13.5 cm long, 2.5 – 5 cm wide, cuneate at the base, shortly acuminate, entire along margin, slightly succulent, coriaceous, with midrib prominent on lower surface, and with 6 – 9 arching lateral veins, dark green above, light green below, old leaves with few sporadic dirty-purple marks.
Inflorescences extra-axillary umbel, commonly with 8 – 25 flowers; peduncle cylindrical, 2 – 2.5 cm long, 2 – 2.5 mm in diam., dark green, tinged with dirty-purple; rachis conical, very short, less than 1 mm long; pedicels light green, slender, 3.5 – 4 cm long, about 0.75 mm in diam. Floral bracts triangular, obtuse, 1.5 – 2 mm long, 0.5 – 0.8 mm broad at the base. Calyx of 5 sepals joined at base, sepals light green, sometimes tinged with dirty purple, lanceolate, obtuse, hairy outside, 7 – 10 mm long, 1 – 1.5 mm wide. Corolla of 5 petals, fleshy, white opalescent, outside with few sparse pink marks, about 2 cm in diam.; petals broadly ovate, glossy, finely pubescent, obtuse to acute, about 1 cm long, 7 mm wide, spreading to reflexed, with margins recurved from rather straight midvein. Coronas of 5 segments, 5 – 7 mm tall, 9 – 11 mm in diam., with elongate, grooved, white to light pinkish nectary between segments; corona segments glossy white, 4.5 – 5 mm long, 3.5 – 4 mm wide (from side view), at the base almost semicircular, apically attenuate into raised, erect, subulate, acute tips approaching together above gynostegium. Gynostegia shortly cylindrical, 4 – 5 mm tall, 6 – 8 mm in diam., anther caps brownish, tinged with purple, corpuscula dark purple-brown, center of anther table brown-purple. Pollinarium with corpusculum, distinct translators (caudicles) and 2 pollinia; corpusculum rhomboid, about 0.5 mm long and wide, translators very short, less than 0.2 mm long, pollinia narrowly oblong, 1.2 – 1.4 mm long, 0.3 – 0.4 mm wide, golden-yellow, germinating crest light yellow, extending to translator. Ovaries 2, free, superior, light green, cylindrical, 2 – 2.3 mm tall, about 0.6 – 0.8 mm wide, extended apically into broad pyramidal stylar head. Fruits often solitary, narrowly-ensiform follicles, 12.5 – 14.5 cm long, 0.8 – 1 cm in diam., dark grey- brown, splitting longitudinally at one side. Seeds narrowly obovoid, slightly flattened, 6 – 7 mm long, 2.6 – 2.8 mm wide, light brown when dry, apically with white silky coma, 1.2 – 1.4 cm long.
Ecology: Hoya lockii is a epiphyte growing on large old trees in pristine primary broad-leaved and mixed (with Dacrycarpus imbricatus) evergreen forests along mountain ridge composed of shale at elevation about 1,000 m a.s.l. Plants commonly growing on large tree branches in sunny canopy zones at 10 – 20 m above ground. Hoya lockii grew in areas in which the present plant species and genera occurred: Dacrycarpus imbricatus, Diplopanax vietnamensis, Dipterocarpus kerrii, Gironniera subequalis , Actinodaphne, Diospyros, Magnolia , Michelia, Parakmeria, numerous palm genera, woody ferns as Alsophila contaminans , species of Tabernaemontana as well as epiphytic ferns and orchids such as Aerides odorata , Bulbophyllum ngoclinhensis, Callostylis rigida , Cleisostoma birmanicum , Dendrobium spatella, Eria obscura, E. thao , Flickingeria angustifolia and Pholidota articulata.
Distribution: Hoya lockii is known only from a very restricted area in the A Luoi district of Thua Thien-Hue province (central Vietnam) at elevation about 1,000 m a.s.l.
IUCN Red List category: Most probably Hoya lockii is a Vietnamese endemic plant. Its known habitat is currently degrading due to deforestation, road construction and other human activities. The species is apparently very rare and only known from one population of less than 50 mature individuals. Therefore, we propose that H. lockii should be treated as a critically endangered species (CR) according to IU CN Red List Categories and Criteria (IUCN, 2010, version 8.1).
Phenology: Full flowering of Hoya lockii was observed during May with fruit formation in June – September.
Etymology: The species is named after the Vietnamese botanist – Prof. Phan Ke Loc.