Decalobanthus sumatranus Ooststr.

18. Decalobanthus sumatranus Ooststr. View in CoL — Fig. 16 View Fig ; Map 10

Decalobanthus sumatranus Ooststr. (1936) 99. — Type: O. Posthumus 571 (holo BO, sheet number 173567), ( Indonesia,) Sumatra, Jambi, near Bangko, along road to Korintji (= Kerinci ).

Stems and branches glabrous, lenticellate. Leaves basally attached, ovate or narrowly ovate, 4–6 by 2–4 cm, bases truncate or slightly retuse; secondary veins 6–7 on either side of the midvein. Inflorescences paniculate, 3- to many-flowered; peduncles 1.5–3.5 cm long; bracts caducous. Flower buds ellipsoid, rounded apically; sepals subequal, 2–2.5 cm long, outer ones basally with 2 prominent dark glands abaxially; corolla salver-shaped, 5–6 cm long, yellow, waxy, tube narrowly obconical to cylindrical, limb 10-lobed, the lobes spreadingreflexed; stamens included, anthers tardily spirally twisting; pistil included, slightly longer than stamens. Fruiting calyxes slightly accrescent, enclosing fruit; sepals blackish abaxially. Capsules 4-valved, depressed globose, 1.8–2 cm diam, brown. Seeds 4, carinate, 4.5–5 mm long, blackish.

Previously published illustrations — Van Ooststroom (1936: 100, f. 1); Van Ooststroom & Hoogland (1953: 457, f. 34); Staples (2013: 10–11, colour photos).

Distribution — Endemic to Sumatra.

Habitat & Ecology — The type collection was found on a roadside in an open sunny place on weathered tuff; recent collections were made on a roadside in secondary regrowth at the edge of an abandoned rubber ( Hevea ) plantation, the soil was reddish clay mixed with stones; elevation 60– 170 m. The vines were populated with large red ants that bit viciously when the plants were handled for collecting. Flowers were just opening at 10:30 a.m. and had no detectable fragrance.

Vernacular name — Akar tanah (Van Ooststroom 1936: 100).

Note — There are some specimens from Borneo that come very near to D. sumatranus in morphological characters and may be conspecific with it, or perhaps they represent a new species; the material is inadequate to settle this matter.

Acknowledgements This study began more than 40 years ago when I prepared a MSc project under the guidance of the late Daniel F. Austin and has progressed incrementally, if intermittently, ever since. I am grateful for the institutional support received from the Bishop Museum (1988–2006), the Singapore Botanic Garden (2007–2013) and, more recently, the Harvard University Herbaria (2018 to present). Along the way I was fortunate to make extended research visits to herbaria on several continents and I am grateful to the directors and staff of the following for welcoming me and providing support for my studies: A, AAU, ANDA, B, BK, BKF, BO, BR, C, E, G, GH, GOET, HITBC, K, KEP, KUN, L, M, NY, P, PSU, QBG, S, SAN, SAR, SING, UPS. I am grateful to Dr Yang Sheng-Zehn and Po Hao-Chen for updating me on the status of D. distillatorius in Taiwan; Mark Gregory Rule and Jane Maestro-Scherer provided field observations on the same species in the Philippines; Barry Hammel, Bill Haber, and Reinaldo Aguilar provided first hand observations for D. discoidespermus , insights regarding its distribution, and the meticulous photo series by Sr. Aguilar clarified the ambiguous staminal filament morphology. Photos of living plants used here are warmly acknowledged,the photographers are credited in the figure captions. Tim Utteridge (K) and Nura Abdul Karim (SING) arranged permission to reproduce illustrations held by their respective institutions.After COVID-19 forced closure of many herbaria in 2020 making study of physical specimens impossible, digital specimen images critical to finalizing this revision were prepared and sent by: Anthony Brach (A, GH); Tiana Rehman, Peter Fritsch (BRIT); Barry Hammel, Reinaldo Aguilar (CR) ; Syahida Emiza binte Suhaimi and Imin Kamin (KEP);Roxali Bijmoer (L, U, WAG); Eva García Ibáñez (MA); Amy Weiss,Matthew Pace (NY); Serena Lee, Derek Liew (SING);Nobuyuki Tanaka (TMS); and Kim Kersh, Ana Penny (UC). I am particularly grateful for their assistance since I could not have completed this revision without it. Finally, I thank Peter van Welzen and Barry Hammel for their thoughtful reviews of the manuscript, which pointed out several opportunities for improvement.

I anticipate that this will be my final taxonomic publication so I wish to thank everyone who has aided me throughout my career in my efforts to understand the intricacies of Convolvulaceae systematics and taxonomy;as Ray Fosberg said it so well, the taxonomy of this family truly is a tangle of morning glories. Any progress I made depended heavily on the assistance so generously provided by others. I am very grateful.