Decalobanthus

Staples, G., 2022, A synoptic revision of the golden glories, genus Decalobanthus (Convolvulaceae), Blumea 67 (1), pp. 37-70 : 38-39

Decalobanthus

Decalobanthus Ooststr.(1936) 99,A.R. Simões & Staples (2017) 568. — Type: Decalobanthus sumatranus .

Merremia Dennst. ex Endl. section Wavula Ooststr. (1939a) 266. — Type: Merremia similis Elmer (= Decalobanthus distillatorius (Blanco) Staples ).

Merremia section Hailale Hallier f. (1913) 379. — Type: Merremia nymphaeifolia (Blume) Hallier f. (= Decalobanthus peltatus (L.) A.R.Simões & Staples).

Woody lianas or large herbaceous climbers; roots sometimes en- larged, tuberous. Indumentum comprising simple trichomes on the plant body (and corollas of D. bimbim , D. boisianus , D. ooststroomii ), sessile glandular hairs on the corolla exterior, stalked glandular hairs on the staminal filaments, and 2–3 mm long, uniseriate trichomes sometimes present on the anther connectives ( D. elmeri , D. peltatus ). Stems twining or prostrate, smooth or striate (never winged), sometimes lenticellate, fistulose or solid. Leaves simple, always entire, petiole basally or peltately attached; venation pinnate, secondary veins arcuate and curving toward margin, flat or impressed adaxially, prominent abaxially. Inflorescences fundamentally cymose, aggregated into panicles or corymbs, sometimes umbelliform, rarely flowers solitary; peduncle long, naked, only branched toward apex; lowermost bract often foliaceous, upper bracts and bracteoles reduced, deciduous. Flowers small to very large, diurnal, odourless; sepals strongly convex (boat-shaped), accrescent and persistent in fruit; corolla usually glabrous outside (sericeous to tomentose in D. bimbim , D. boisianus , D. ooststroomii ), granulose-glandular outside with tiny golden glands (in D. bracteatus , D. elmeri , D. mammosus , D. pacificus ), midpetaline bands without distinct dark lines; stamens included or protruding, lower filaments adnate to corolla tube, margins glandular hairy, upper filaments free, thread-like, glabrous, anthers spirally twisted at dehiscence, sometimes tardily so, in D. elmeri and D. peltatus with very long tufts of hairs on the anther connectives; pollen almost exclusively tricolpate. Fruits of 3 distinct types: in most species valvate capsules, the 4 valves sometimes splitting into several smaller segments, distinctively bicoloured: the exocarp partially delaminating so that the lower fruit wall remains dark brown or black and the apical portion is straw-yellow after the exocarp falls away; in D. borneensis , D. bracteatus , and D. pulcher indehiscent berries, blackish, dry, 2- to many-seeded; in D. discoidespermus a chartaceous utricle, brittle, translucent, indehiscent, 1-seeded. Seeds usually 4, or 10 (or more) and carinate, or 1 and depressed quatrefoil, pubescent at first, sometimes with longer hairs along the angles, often glabrescent later. Cotyledons 2, epigeous, petiolate; blades broadly obovate, apices deeply emarginate.

Distribution — 18 species, centered in Malesia and continental Southeast Asia and extending eastward across the tropical Pacific with one species found in the Neotropics. A single species, D. peltatus , extends its distribution westward to coastal East Africa, Madagascar and throughout the Indian Ocean Islands, as well as eastward across the Pacific as far as the Hawaiian Islands, where it is naturalized. The greatest concentration of species occurs on Borneo, where four endemic species are found. The recent report ( Simões et al. 2020) that Decalobanthus occurs on ‘Santa Cruz Island, North America’ is erroneous.

Note — The polymorphism in fruit types in Decalobanthus seems surprising at first, because we have historically been trained to think one genus has only one fruit type. However, molecular phylogenetics has turned this received wisdom upside down and we are having to revise our thinking about the taxonomic importance of fruit types and dehiscence mechanisms. The fruits of Decalobanthus will be explicated more fully in a paper devoted to fruit types and their evolutionary implications in the Convolvulaceae , now in preparation.