Small tree, to 4 m tall; leaf-bearing branches 5-8 mm diam, the internodes 4-21 cm long. Leaves in 1-5 clusters at apices of branches, 9-16 per cluster. petioles 0.5-5 cm long, 3-5 mm thick at blade juncture; blades oblanceolate to narrowly oblanceolate, attenuate to acuminate at apex, tapered from middle to an acute base, 30-72 cm long, 4.5-10 cm wide, glabrous, chartaceous, the margins serrate apically, entire basally; lateral veins in 22-31 pairs, the intramarginal vein well developed. Inflorescences subterminal, infrequently cauline, with up to 13 flowers; rachis 5-6.5 cm long, 9-12 mm wide at base; pedicels 6-7.5 cm long; basal bract 1, triangular to narrowly triangular, 8-12 mm long, 5-7 mm wide, the bracteoles 2, ovate to narrowly ovate, cucullate, 7-11 mm long, 5-8 mm wide, inserted slightly above the middle; flowers 10-14 cm diam; calyx lobes 4, broadly triangular, 4 mm long, 14 mm wide; petals 8, narrowly obovate to oblanceolate, 5.5-6.5 cm long, 2-2.5 cm wide, light pink throughout; androphore connate at base, light pink, 11-12 mm high; outermost filaments white at the base, dark pink above, 18-19 mm long; anthers yellow, 2.5-3.5 mm long; ovary puberulent, 5-locular, white-pubescent at apex; ovules 20-30 per locule; style conical, 3 mm long; stigma with 5 (6) lobes. Pyxidia globose, truncate at apex, 5 cm long, 5 cm wide, obscurely 4-costate, the calyx lobes persistent, the operculum nearly as wide as the fruit; funiculi white, 5 mm long, 4-5 mm wide; seeds several, cream-colored, irregularly 3-sided in cross section, 3-3.5 cm long, 2.2-2.4 cm diam, surrounded by a creamy white endocarp. Foster 2790 (holotype, MO; isotype, F). Apparently rare; collected once by R. Foster near the junction of Snyder-Molino and Wheeler trails. The species has been observed in flower in June and July, and with mature fruits in September and October. The closest relative of G. fosteri is G. angustifolia Benth. of the dry coastal forests of Ecuador. The principal difference between these two species is the glabrous lower leaf surface of G. fosteri in contrast to the pubescent surface of G. angustifolia. The species is easily confused with the much more abundant G. superba, but is distinguished by having its leaves grouped in several verticils at the branch ends instead of scattered along the ends of the branches, by its mostly terminal instead of cauline inflorescence, by its calyx of four broadly triangular lobes (the calyx in G. superba is entire), and by its petals being light pink throughout instead of white with flushes of pink. Also the fruit has a white instead of orange mesocarp at maturity, and the leaves of G. fosteri tend to be smaller than leaves of G. superba.