Cymbosema Benth., J. Bot. (Hooker) 2: 61. 1840.

Queiroz, Luciano Paganucci de & Snak, Cristiane, 2020, Revisiting the taxonomy of Dioclea and related genera (Leguminosae, Papilionoideae), with new generic circumscriptions, PhytoKeys 164, pp. 67-114 : 67

2. Cymbosema Benth., J. Bot. (Hooker) 2: 61. 1840.

Type.

Cymbosema roseum Benth.

Description.

Woody twining vines. Stipules basifixed, not prolonged beyond their base. Leaves pinnately trifoliolate, long, stipellate, leaf rachis 5-20 mm. Inflorescence an erect pseudoraceme, nodes multiflorous, sessile, secundiflorous; bracteoles chartaceous. Flowers with calyx chartaceous, campanulate, the four lobes of almost the same length, upper lobe entire, triangulate, obtuse, lower lobe ovate and acute; petals membranous, bright red, standard petal spreading, rarely reflexed, ecallose, provided with two basal and reflexed auricles, pubescent towards the apex on the outer surface, wing petals as long as the keel, oblong to obovate, provided with a basal spur at the upper margin, keel petals straight, oblanceolate, margins smooth; androecium diadelphous, the vexillary stamen free, the nine remainder fused but free distally, anthers monomorphic, all 10 stamens fertile; intrastaminal nectary disc entire, collar-shaped; pistil almost straight, ovary mostly 5-6-ovulate, sessile, style not swollen. Fruits shortly oblong, 2.4-2.5 × longer than wide, up to 2 cm wide, elastically dehiscent, the thin woody valves explosively twisting to release the seeds, upper margin straight, lacking ribs or wings, style persistent and extending as a downcurved rostrum. Seeds small, up to 10 mm long and 6 mm wide, lenticular (slightly biconvex); testa hard (bony), smooth; hilum linear, encircling almost half of the seed’s circumference. (Fig. 2E-F ).

Discussion. Our results support the recognition of Cymbosema as a monospecific genus, as originally proposed by Bentham (1840, 1859) and maintained by Maxwell (1970). Zamora (2000) synonymised Cymbosema in Dioclea , a proposal that is not supported by our results, which recovered Cymbosema as sister to Cleobulia rather than to Dioclea .

Cymbosema is diagnosed as having flowers with a diadelphous androecium with the vexillary stamen free, petals bright red, the standard petal spreading (only rarely reflexed), keel petals with smooth margins and fruits oblong and falcate.

Distributed in the Amazon region, extending north to the Pacific coast of Mexico in wet forests.

Figures

Figure 2. Representatives of the clade A. Cleobulia coccinea (Mart. ex Benth.) L. P. Queiroz A flowering vine showing the arcuate inflorescences B detail of the inflorescence showing resupinate flowers; the inset highlights the wing petals (w) much shorter than the standard (s) and keel petals (k) C fruit (from Queiroz 16029). Cleobulia diocleoides Benth. D a resupinate flower showing the reduced wing (from Queiroz 16036). Cymbosema roseum Benth. E part of the inflorescence showing the bird pollinated flowers and the free adaxial stamen (arrow) F immature fruits showing the characteristic broad oblong fruit body and the long beak (from Cardoso 2868). Dioclea virgata (Rich.) Amshoff G flowers (from Cardoso 2374) H fruits (from Cardoso 2100). Dioclea fimbriata Huber I flowers (from Snak 1223). Dioclea burkartii R. H. Maxwell J a seed showing the marbled testa and the elongate hilum encircling about half of its circumpherence (arrow; from Snak 826). Dioclea apurensis K flowers (from Queiroz 13035). Photos A-D, J-K: L. P. Queiroz; E-H: D. Cardoso; I: C. Snak.