Hoya graveolens Kerr

Hoya graveolens Kerr View in CoL — Fig. 2 View Fig

Hoya graveolens Kerr (1939) View in CoL 461. — Typus: Kerr 4245, Thailand, Sriracha, 15 May 1920 (lecto BM, designated here; iso K, P).

Hoya graveolens View in CoL was described from a specimen collected in Sriracha , Thailand by Kerr in 1920. Kerr selected as type his collection Kerr 4245 but did not indicate in which herbarium it was deposited thus a lectotype has to be selected. We found duplicates in BM, K and P and we hereby select the BM specimen as lectotype since it is a complete specimen with leafy stems and flowers. It is also the only specimen belonging to Kerr’s own herbarium (labelled: Herb. A. F. G. Kerr – Bequeathed 1942) and bears pencilled drawings and measurements of the flowers likely by Kerr’s hand .

Terrestrial or lithophytic decumbent climber with white latex. Leafy stem slender, cylindrical, green, c. 5 m long, 2 –7 mm diam, glabrous, older stems leafless, rust-brown with brown spots, with swollen nodes, glabrous. Internodes 2–16 cm with inactive adventitious roots below old nodes, located at or up to 2 mm below the nodes. Leaves petiolate; petiole curved or slightly twisted, light green (5–)7–12 by 1.5 –3.5 mm, glabrous; lamina fleshy, coriaceous when dry, obovate-elliptic, dark green adaxially with many small whitish spots, light green abaxially, sometimes bearing purple spots, 5.4 –7.8 by 3 –5.7 cm, glabrous, apex shortly acuminate or cuspidate, base cuneate or rounded, penninerved, main vein depressed on adaxial surface, evident on abaxial surface, secondary veins indistinct on fresh leaves, evident when dry, 3(–5) pairs, at 45– 60°. Inflorescence positively geotropic, pseudo-umbelliform, globose, c. 5 cm diam, up to 20-flowered; peduncle extra-axillary, green to purple-brown with few brown spots, perennial, presenting scars of previous flowerings, (17–)30 – 38(–55) mm long, c. 2 mm diam in the central portion, up to 3.5 mm at the apex, glabrous; pedicels terete, green or purple-brown, 1.3– 2 cm long, c. 0.6 mm diam, sparsely hirsute. Calyx purplish green to light purplish, 3.4 –4.1 mm diam, lobes triangular-ovate 1.7–2 by 0.8 –1 mm, apex acute with a membranaceous margin, sparsely hairy inside, outer glabrous. Buds slightly 5-angled, creamy-white. Corolla rotate, concave, white adaxially and purplish white abaxially, 1.5 –1.6 cm diam, lobes rhomboid-ovate, membranous, 8 –8.3 mm long with free part 5– 5.5 by 5 –6 mm, margin reflexed, apex pointed and recurved, pilose throughout, hair length near corona 375–450 μm, near apex 300–375 μm. Corona staminal, translucent purplish white, turning purple at base, 5.5– 5.7 mm diam, 2.5– 3 mm high, glabrous; lobes ovate, held horizontally, 2.5 – 3 by 1.3 –1.5 mm, inner process acute, outer process round, inner process exceeding anthers 1–1.4 mm. Pollinarium (all measurements approximate) 980 by 700 μm, pollinium oblong, 830 by 300 μm, apex obliquely truncate, base acute-round, retinaculum 370 by 180 μm, caudicle 100 μm long with appendages. Ovary bi-carpellate, each carpel ovate, light greenish, 1.2–1.5 by 0.5–0.7 mm, glabrous. Follicles fusiform, yellow dotted dark red-black c. 8 cm by 7 mm; seeds flattened, c. 5.5 by 1 mm, comose.

Distribution — So far only observed on three small karst hills along the coast in Kiên Giang Province, southern Vietnam.

Habitat & Ecology — Terrestrial or lithophyte, decumbent or weakly climbing, found in shaded areas at 0–110 m asl. The prevailing climate in this area is monsoon subequatorial climate with an annual rainfall of 2100 mm and average temperature of 27.4 ° C (Nguyễn et al. 2000). This species has been observed flowering in Vietnam from April to May, in accordance with the flowering period observed in Thailand (March to May) .

IUCN assessment — In Vietnam, H. graveolens has been observed only on the isolated karst hills of Kiên Giang Province in a total area of less than 3 km 2. This area is being destroyed by human impacts such as fuel wood cutting, small scale agriculture, and exploited for cement production, making the species likely to become threatened in the future. Based on the IUCN Red List criteria (IUCN Standards and Petitions Subcommittee 2011), we assign a provisional conservation status of Near Threatened (NT).

Specimens examined. THAILAND, Collins 136 B ( K, P), Chonburi Province, Sriracha , Apr. 1913 ; Kerr 4138 ( K), 29 Mar. 1920 ; Kerr 4130 A ( K), 18 May 1920 ; Maxwell 76-313 ( L), Nakorn Ratchasima Province, Sikiew District, Khao Phrik , 8 May 1976 ; Maxwell 93-387 ( L), Chonburi Province, Si Chang Island , 7 May 1993 . – VIETNAM, Lý 521 ( HN, P, SING, VNM), Kiên Giang Province, Kiên LƯƠng District , Bình An commune, 50 m asl, N10°08'23", E104°38'27", 9 Apr. 2009 GoogleMaps ; Lý et al. 61 ( VNM), Kien Giang Province, Hang Tiền Karst Hill , 45 m asl, N10°11'04", E104°35'41", 04 May 2007 GoogleMaps ; Lý et al. 125 ( VNM), Mo So (Bai Voi) Karst Hill , 47 m asl, N10°13'21", E104°36'54", 16 Apr. 2008 GoogleMaps ; Lý et al. 185 ( VNM), Bà Tài Karst Hill , 99 m asl, N10°10'17", E104°36'07", 12 Apr. 2008 GoogleMaps .