Decalobanthus boisianus (Gagnep.) A.R.Simões & Staples

2. Decalobanthus boisianus (Gagnep.) A.R.Simões & Staples View in CoL — Map 1 View Map 1

Decalobanthus boisianus (Gagnep.)A.R. Simões & Staples (2017) View in CoL 569. — Ipomoea boisiana Gagnep. (1915a) View in CoL 141. — Merremia boisiana (Gagnep.) Ooststr.(1939b) View in CoL 343. — Lectotype (designated by Van Ooststroom (1939b)

344): Bois 138 (lecto P [P00608899]), ( Vietnam,) Tonkin, ‘montagnes du Caï Kinh, route de Than Moï à Van Linh’.

Stems and branches usually glabrous, not lenticellate. Indumentum (when present) drying greyish yellow. Leaves basally attached, blade subcircular or broadly ovate, bases shallowly cordate; secondary veins 6–8 on either side of the midvein. Inflorescences many-flowered, crowded panicles or thyrses; peduncles 5–24(–35) cm; bracts caducous. Flower buds bluntly ovoid; sepals subequal or outer 2 shorter, broadly ovate, 0.4– 0.7 cm long, apically obtuse or rounded; corollas broadly funnelform, 1.2–1.7(–2.1) cm long, yellow, midpetaline bands sericeous outside; stamens included, subequal, anthers belatedly curled; pistil included. Fruiting calyx persistent, slightly accrescent, cupping fruit base; sepals convex, margins entire or erose. Capsules conical-ovoid, 1–1.2 cm long, 4-valved, glabrous, brown below, apically straw-yellow. Seeds broadly trigonous-ovoid, c. 5 mm long, angles densely scaly pubescent.

Previously published illustration — Staples (1996: 187, f. 1).

Distribution — China ( Guangdong, Guangxi, Guizhou, Hainan, Hunan, Yunnan), newly reported from Taiwan ( Chen et al. 2022), Laos, Vietnam.

Habitat & Ecology — In diverse habitats ranging from primary broadleaf evergreen forest and forest margins, to secondary forests along roadsides, thickets, shaded areas in valleys, riversides, swamps, on various soil types including dry sandy soil, rocky hillsides, clayey shale, wet swampy muck, and sandstone; elevation ranges from (120–)300–900(–1435) m.

Several collectors report that the flowers are fragrant. Recently D. boisianus has been reported to be an invasive species in China ( Chen et al. 2005) and potentially so in Taiwan ( Chen et al. 2022).

Vernacular names — China: Duo hua shan zu cai ( Jiang 7710), jin zhong teng ( H. Sun 1347), ka chue tang ( Lei 865), seng geng man (Cantonese, Lau 155). Vietnam: Dô ut ( Poilane 3879), dok khua khan muok ( Spire 1049), prỏ he (Moï dialect, Poilane 13305).

Uses — The stem is used medicinally to treat anaemia ( Fang & Staples 1995: 299).

Notes — There has been much confusion in herbaria between D. boisianus and two species of Ipomoea , I. sumatrana (Miq.) Ooststr. and I. staphylina Roem. & Schult. ; Staples (1996) clarified the differences, provided a key and diagnostic illustrations to distinguish these three taxa. The confusion began with misidentifications made by E.D. Merrill on specimens collected from Hainan Island in the 1920s–30s, which were widely distributed to many herbaria with the wrong names. Such errors persist for decades and are perpetuated in publications based on the misidentified specimens. The confusion was again elu- cidated by Wang et al. (2007).

The diagnostic characters useful for recognizing D. boisianus are: the inflorescence peduncle is typically longer than the subtending leaf; the inflorescence architecture is complex, multibranched, flat-topped, corymb-like or thyrsiform; the corollas are bright yellow with pubescent midpetaline bands on the outside. The genuine distribution for D. boisianus has been muddied by taxonomic confusion as noted above and explained further below (under var. fulvopilosus ) but it seems clear that this species ranges widely across southern subtropical China and southward into Laos and Vietnam. The distribution in China is peculiar: the single isolated collections from Hunan ( Morse 627) and Guizhou ( Z.Y. Cao & Z.T. Wang 165) suggest that this species once grew, and perhaps still does grow, much further north than what is now documented by voucher specimens in the CVH. Does D. boisianus occur in Sichuan? There are no records from Sichuan province in the CVH, but the possibility cannot be excluded because the one Guizhou collection came from the border with eastern Sichuan. The single collection from Guangdong province was made in the metropolitan area for Guangzhou City; the documenting voucher specimen ( B.H. Chen 4193) was written up as a first provincial record as well as to point out that D. boisianus can be invasive in intact forest ecosystems ( Chen et al. 2005). Still, there is no reason why D. boisianus should not occur in coastal subtropical Guangdong, if there is any suitable habitat for it in the highly developed landscape there.All in all, the Chinese distribution is patchy and imperfectly known and further field work is needed to improve our knowledge of this species distribution and abundance. Newly reported as a naturalized species from northern Taiwan ( Chen et al. 2022).

Historically, Chinese floras recognized two varieties, separable by the following key:

Key to the varieties

1. Branchlets, petioles, leaves, peduncles, and pedicels glabrous or nearly so............................................. a. var. boisianus View in CoL (see under the species)

1. Branchlets, petioles, leaves, peduncles, and pedicels greyish yellow tomentose................. b. var. fulvopilosus View in CoL