Decalobanthus ooststroomii Staples

14. Decalobanthus ooststroomii Staples View in CoL , nom. & stat. nov. — Fig. 10 View Fig ; Map 10

Merremia boisiana (Gagnep.) Ooststr. var. sumatrana Ooststr., Blumea View in CoL 3 (1939b) 344, non D. sumatranus Ooststr. View in CoL — Decalobanthus boisianus var. sumatranus (Ooststr.) A.R. Simões & Staples (2017) View in CoL 569. — Type: LÖrzing 4723 (holo L [L 0836954]; iso BO sheet numbers 1705910, 1705925, 1705926), ( Indonesia,) Sumatra, Sibolangit.

Stems and branches grey to fulvous pubescent, later glabrescent, not lenticellate. Leaves basally attached, broadly ovate, up to 20 by 16 cm, bases subcordate to shallowly cordate, abaxially greyish pubescent; secondary veins 6–8 on either side of the midvein. Inflorescences many-flowered, crowded panicles or thyrses; peduncles 8–16 cm long. Flower buds ovoid, obtuse to acute; sepals 4–6 mm long, rounded to obtuse; corollas flaring funnelform, 1.1–1.5 cm long, white, base of tube inside pale yellowish, limb erect, crenulate; hairs on midpetaline bands drying white on darker background; stamens and pistil included. Fruits and seeds not seen.

Distribution — Endemic to northern Sumatra ( Aceh, Sumatera Utara).

Habitat & Ecology — Collectors report it is common in thickets and secondary regrowth, at edges of recently logged primary forest, in clearings, sprawling on roadsides, the soil types not stated; elevations ranging from 50–600(–1200) m.

Nomenclature — Because the epithet sumatranus is preoccupied in Decalobanthus , I propose a new name for this taxon at specific rank: D. ooststroomii . Simon Jan Van Ooststroom (1906–1982) first recognized this taxon and he made exceptional contributions to the study of Malesian and Asian Convolvulaceae .

Notes — Known from just a few collections from northern Sumatra these Sumatran populations are quite distinct from the continental Asian ones and I am elevating them to specific rank. Visits to BO in 2008 and ANDA in 2012 did not disclose any recent collections. Interestingly, Van Ooststroom (1939b: 343) singled out Yates 975 from East Coast Sumatra as being the typical var. boisiana while all other specimens collected from Sumatra he considered var. sumatranus . The Yates duplicates were distributed without label data; only the set in the UC herbarium has complete field notes attached and these describe a vine with white flowers, so I am including Yates 975 in my concept for D. ooststroomii . Wang et al. (2007) reduced var. sumatranus under their concept of M. boisiana var. fulvopilosa , which I do not accept.

Photos of live plants from Sumatra were sent to me for identification (H. Rahmadani, pers. com. 2011–2012), but no vouchers were seen. One of Rahmadani’s photographs was reproduced in the recent publication by Simões et al. (2020: f. 2D) and while correctly identified as var. sumatranus the photo is wrongly attributed to Jana Leong and said to be from Vietnam. The caption for this f. 2 has other errors and misattributions and compounds the confusion for D. boisianus by wrongly identifying f. 2E as yellow-flowered var. sumatranus ; this photo actually shows D. bimbim .