Decalobanthus mammosus (Lour.) A.R.Simões & Staples

Staples, G., 2022, A synoptic revision of the golden glories, genus Decalobanthus (Convolvulaceae), Blumea 67 (1), pp. 37-70 : 56

13. Decalobanthus mammosus (Lour.) A.R.Simões & Staples — Fig. 9 ; Map 8

Decalobanthus mammosus (Lour.) A.R. Simões & Staples (2017) 571. — Convolvulus mammosus Lour. (1790) 108. — Ipomoea mammosa (Lour.) Choisy (1834) 475. — Merremia mammosa (Lour.) Hallier f. (1897) 164. — Lectotype (designated by Simões & Staples 2017: 571): [icon] Rumphius, Herb. Amboin. 5 (1747) 370, t. 131.

Ipomoea gomezii C.B.Clarke in Hook.f. (1883) 211, Gagnep.(1915b) 254. — Lectotype (designated here,see note): Gomez s.n. (lecto K [ K000830866 ]; isolecto K [ K000830867 ]),Burma,( Myanmar, Tenasserim Division ,) ‘ Tavoy’.

Stems and branches glabrous, not lenticellate. Roots fasciculate tubers to 25 cm long. Leaves basally attached, orbicular to transversely elliptic, 6–12 by 5–15 cm, bases cordate; secondary veins 7–9 on either side of the midvein. Inflorescences cymose-paniculate, 3–30-flowered; peduncles 3–15 cm long; bracts deciduous. Flower buds ellipsoid, acute; sepals subequal, convex, glabrous, outer 3 broadly ovate to broadly elliptic, 24–36 mm long, apices obtuse; corollas broadly funnelform, 7–12 cm long, pale yellow or white with yellow inside tube, outer surface minutely gland-dotted; stamens included, subequal, anthers strongly spiralling; pistil included, equalling or shorter than stamens. Fruiting calyxes accrescent, enclosing fruit. Capsules 4-valved, ovoid, 2–2.5 cm long; valves with secondary splits that do not reach apex. Seeds 4, c. 8 mm long, brown pubescent, margins with 5–8 mm long, paler hairs, later glabrescent.

Previously published illustrations — Staples (2010: colour plate LI, f. 3.1, 3.2; 2018: 295, f. 14.12).

Distribution — India ( Assam, Nagaland), Myanmar, Thailand, Vietnam.So far not documented from Bangladesh, Laos or Cambodia but almost certainly present there. Formerly, and perhaps still, cultivated in Bogor Botanical Garden ( Indonesia, Java) and Calcutta Botanic Garden ( India, West Bengal).

Habitat & Ecology — Rampant climber forming vine blankets over trees, thickets, along roadsides in various habitats including: mixed deciduous forest, disturbed, degraded overgrown roadside thickets in primary evergreen seasonal hardwood forest, hill evergreen forest, on diverse soils including karst limestone, solid sandstone hillsides with shallow soil pockets, shale bedrock, and ‘salty’ soil; at elevations from 50–450 m in Thailand and 1220–1525 m in Myanmar. Full sun exposure and moisture regimes varying from seasonally dry to continuously moist.

Vernacular names — Thailand: หัวล้านชนกน (hua lan chon kan) ( Songkhla & Khunwasi 1993: 50). Vietnam: Khoai tù ( De Loureiro 1790: 108).

Uses — The tubers are edible and used medicinally in Java ( Backer 33473).

Typification — Clarke (in Hooker 1883) based his Ipomoea gomezii on two collections ( syntypes); only one collection was found in Kew, the Kurz specimen cited from the ‘Andamans’ was not located. The lectotype chosen fixes the application of Clarke’s name and reduces it to synonymy.

Note — Van Ooststroom (in Van Ooststroom & Hoogland 1953: 451) stated this is a perennial plant with stems that grow annually from the underground tubers. Where I have collected the plants in western Thailand they are enormous lianas, covering tall trees. It is difficult to imagine such rampant growth pro- duced annually; this needs to be investigated further. There is geographical variation in corolla colour: in Myanmar and the adjacent western provinces of Thailand the corollas are large ( 8–12 cm long), pure white with a yellow tube; further east in the Central and Eastern regions of Thailand the corollas are smaller ( 7–8 cm long), pale yellow with a darker tube.

One of the inexplicable oddities about this species is its seeming rarity (or absence) in Vietnam. De Loureiro (1790: 108) stated in the protologue that his new species was ‘ frequenter cultus in agris Cochinchinae ’. No De Loureiro specimen for it has been found. Only one later collection has been seen from Vietnam: F.J. Harmand collected it on the island of Poulo Condor in the late 19th century. A thorough search of the Paris herbarium in 2015 disclosed no other collections of D. mammosus from Vietnam, Cambodia nor Laos. It would not be easy to overlook such an expansive climber with large, eye-catching flowers and one has to wonder whether De Loureiro’s comment was accurate at the time or if this species later disappeared from Vietnam.

Figures

Map 8 Distribution of Decalobanthus eberhardtii (Gagnep.) A.R.Simões & Staples (■); D. mammosus (Lour.) A.R.Simões & Staples (wild plants = ●, cultivated plants = ●).

Fig. 9 Decalobanthus mammosus (Lour.) A.R.Simões & Staples. a. Habit with pale yellow colour morph; b. flower in frontal view, white colour morph; c.opened corolla showing spirally twisting stamens and pistil;d.hesperiid visitor in pale yellow flower;e.dehiscing fruits showing delaminating capsule valves with multiple secondary splits in valves (a, d, e: Preecha Karaket, voucher: Staples et al. 1336 in SING; b, c: George Staples, voucher: Staples et al. 1346 in SING).