Plathymenia Benth., J. Bot. (Hooker) 4: 333. 1841.

Figs 127, 129

Pirottantha Speg., Anales Soc. Ci. Argent. 82: 226. 1916 (publ. 1917). Type: Pirottantha modesta Speg. [= Plathymenia reticulata Benth.]

Type.

Plathymenia reticulata Benth.

Description.

Unarmed deciduous trees (Fig. 127B), 2.5-12 (40) m; stems dark, terete, glabrous to glaucous, waxy; brachyblasts absent. Stipules rudimentary or caducous. Leaves bipinnate; extrafloral nectary absent or occasionally with an inconspicuous lump on the petiole; pinnae 3-10 pairs, opposite, sub-opposite or distinctly alternate, terminating in an adaxial, crateriform nectary; leaflets 6-20 per pinna, mostly alternate, conspicuously brochidodromous. Inflorescences spiciform racemes in leaf axils or more frequently above the axils (Fig. 127F). Flowers pedicellate, pedicels persistent and peg-like after abscission of unfertilised flowers; calyx 5-toothed, campanulate; petals 5, pale green, glabrous or sparsely pubescent on the apex, apparently separate to base; stamens 10, filaments white, free to the base, connective somewhat enlarged, anther glands large, apical, stipitate, round; pollen in tricolporate monads with a smooth (perforated) exine with columellae; ovary stipitate, stigma tubular. Fruits linear-oblong, tardily dehiscent through both sutures, strongly dorsiventrally flattened, the valves coriaceous (Fig. 127J), endocarp chartaceous forming membranous rectangular packets around the seeds, separating from the valves at maturity, and dispersed with the seeds enclosed (Fig. 127K). Seeds dorsiventrally flattened, the testa hard, pleurogram present, closed.

Chromosome number.

2 n = 26 (Goldblatt 1981b).

Included species and geographic distribution.

Monospecific ( P. reticulata), restricted to South America, primarily in central and eastern Brazil but extending to east-central Paraguay, Bolivia, and southern Suriname (Fig. 129).

Ecology.

Mainly in deciduous rocky cerrado (savanna) (Fig. 127B) and sparse cerradão woodland, extending weakly into wetter coastal Mata Atlântica forests and seasonally dry tropical forests, mainly 300-1100 m elevation.

Etymology.

From Greek, platy (= flat) and hymen (= membrane), in reference to the membranous endocarp breaking up into papery square envelopes in which the seeds are dispersed (Fig. 127K).

Human uses.

The timber of P. reticulata is used for furniture and fence posts. The bark has been used medicinally (Warwick and Lewis 2003).

Notes.

Plathymenia forms its own monogeneric (and monospecific) lineage embedded in the grade that subtends the core mimosoid clade (Fig. 126). In fruit, Plathymenia is unusual among Mimoseae in its endocarp forming papery packets around the seeds (Fig. 127K). Previously two species were recognised in the genus, however Warwick and Lewis (2003) concluded that there is only a single polymorphic species, noting that the various morphological variants do not correlate with geography or ecology.

Taxonomic references.

Bentham (1876); Warwick and Lewis (2003), both with illustrations.