In the past, the monogeneric family Balanopaceae oscillated in its systematic position between the vicinity of Euphorbiaceae and Fagales. RbcL analysis placed Balanopaceae in Malpighiales (Litt & Chase 1998), and thus rather favors the first interpretation. Balanopaceae appear as sister to a clade composed of Chrysobalanaceae and Dichapetalaceae/Trigoniaceae (Chase et al. 2002). Among the polyphyletic Euphorbiaceae s.l., the closest relatives of this clade seem to be Phyllanthaceae (Phyllanthoideae) and Pseudanthaceae (Oldfieldioideae). Here we present the first more detailed study on the morphology and anatomy of female flowers and cupules of Balanops, based on fresh and liquid-fixed material of the type species, B. vieillardii. We show that some earlier observations on herbarium material perpetuated in the literature are inaccurate or incorrect. The ovary is completely bi- or trilocular. Placentation is axile, and neither parietal nor basal (although near the base of the locule). The ovules are bitegmic, not unitegmic. In the larger ovule of each locule, the micropyle forms a longitudinal slit, and is not covered by a funicular obturator. The cupule is simple, it is formed by a number of spirally arranged, crowded bracts below the base of the terminal female flower, and in the axil of several bracts additional female flowers may be produced, whereas in Fagaceae the cupule represents a complex dichasial ramification system without flowers in the axil of cupular bracts. The structural results support a position of Balanopaceae in Malpighiales, as suggested by molecular studies, rather than in Fagales.

Key words: Balanopaceae, Balanops, floral structure, gynoecium, Malpighiales, ovules