The ovule primordium of Humiria balsamifera is trizonate. The ovule is anatropous, bitegmic and crassinucellate. Both integuments are of dermal derivation and initially mainly two- to three-layered. The inner integument soon becomes three-layered by periclinal divisions of its inner layer. The seed coat structure is described for the first time. Although the endocarp has taken over the function of seed protection, the seed coat shows a clear differentiation. The lignified fibrous exotegmen is the most characteristic layer. Also the exotesta has thickened, lignified cell walls. The other layers of the seed coat remain thin-walled. A distinct nucellar cuticle and a thin layer of adjacent nucellar cells lie inside the seed coat. The nuclear endosperm later becomes cellular. The ovule and seed characters of Humiria closely resemble those of the other families in the Malpighiales/Linales complex studied.