Cylicodiscus Harms, Nat. Pflanzenfam. Nachtr. II-IV, 1: 192. 1897.

Figs 132, 133, 134

Cyrtoxiphus Harms, Nat. Pflanzenfam. Nachtr. II-IV 1: 203. 1897. Type: Cyrtoxiphus staudtii Harms [= Cylicodiscus gabunensis Harms]

Type.

Cylicodiscus gabunensis Harms

Although Cylicodiscus is clearly a member of the core mimosoid clade, its phylogenetic relationship to the Prosopis clade, from which it is separated by a very short branch, and to the Neltuma clade, are not well-resolved (Fig. 132). For this reason, Cylicodiscus is here presented as a separate monogeneric lineage rather than being included in another named clade of Mimoseae .

Description.

Very large trees 25-65 m, to 70+ cm trunk diameter, bole straight cylindrical, thick wandering buttresses with knee-like outgrowths (Fig. 133A-C) and small adventitious roots at base; trunks of young trees armed with sharply tipped pyramidal scattered woody protuberances (Fig. 133D); bark fibrous, rough, black-brown; slash brownish-yellow or reddish-orange, wood very hard, brachyblasts absent. Stipules caducous. Leaves bipinnate, petiole bearing a round, sunken nectary at the apex; pinnae 1-3 pairs, opposite; leaflets 3-7 pairs per pinna, alternate, venation brochidodromous. Inflorescences of solitary, axillary spiciform racemes; unfertilised flowers abscising post-anthesis to leave peg-like pedicels (Fig. 133E). Flowers white; hypanthium absent; calyx 5-lobed, valvate; petals 5, valvate, free; stamens 10, free, anthers dorsifixed, bearing an apical globose gland; intra-staminal disk present, well-developed; pollen in tricolporate monads, exine smooth (perforated), columellae present; ovary sessile/stipitate, stigma porate. Fruits pendulous, linear oblong, strap-like, up to 1 m long, dehiscent along the ventral suture (Fig. 133F), flattened, woody, ca. 10-seeded, exocarp cracking when mature, sutural ribs flattened, 5 mm wide; mesocarp of two layers, a black glassy layer underlying the endocarp and a reticulate, cardboard-like fibrous layer below that; endocarp smooth, fibrous. Seeds ellispoid, large, to 13 cm long and 2 cm wide (Fig. 133I) surrounded by a thin papery wing 6 mm wide, testa thin, papery, pleurogram absent, the funicle attached to the short end of the seed.

Chromosome number.

Unknown.

Included species and geographic distribution.

Monospecific ( C. gabunensis), west and central Africa in Cameroon, Côte d’Ivoire, Equatorial Guinea, Gabon, Ghana, and Nigeria, widespread but apparently uncommon (or perhaps just difficult to collect!) (Fig. 134).

Ecology.

Very large canopy-emergent trees with massive crowns in well-drained evergreen lowland tropical Guineo-Congolan rainforest (Fig. 133A-C) and moist semi-deciduous forests. In common with several other genera of Mimoseae such as Fillaeopsis and some species of Entada, the flowers of Cylicodiscus are very small, yet give rise to very large fruits. Seeds winged and likely wind-dispersed (Fig. 133G-I).

Etymology.

From Greek cylico (= cup-shaped) and Latin discus (= disk), referring to the cup-shaped floral disk to which the stamens are attached.

Human uses.

The timber of C. gabunensis is very dense and used in heavy construction, for railway sleepers and flooring (Ndonda Makemba et al. 2019).

Notes.

Phylogenetically, Cylicodiscus is separated by a very short branch from the Prosopis clade (Fig. 132). It is perhaps notable that both genera of the Prosopis clade, Prosopis L. and Indopiptadenia Brenan, share internodal prickles and/or sharp pyramidal scattered woody protuberances on the stem and shoots with Cylicodiscus (Figs 133D, 135B, C, E). Although the relationship of Cylicodiscus to the Prosopis and Neltuma clades remains uncertain, Cylicodiscus is clearly a member of the core mimosoid clade and shares presence of armature with the other two first-branching lineages of that clade.

Taxonomic references.

Aubréville (1959) with illustration; Burkill (1995); Ndonda Makemba et al. (2019); Villiers (1989) with illustrations.