Morphology and physiology of fruit and seed development were compared in wild populations of two shrubs, Rhus aromatica and R. glabra (Anacardiaceae) in 1996 and 1997. Flower buds of R. aromatica formed in August, and plants flowered and set fruits the following April and June, respectively, whereas R. glabra formed flower buds after the plants leafed-out in early June and flowered in late-June to early-July, one week after the endocarp of R. aromatica fruits had become impermeable to water. However, the two species showed strong similarities in fruit and seed development. It took only about 2 months for their flowers to develop into drupes. The single sigmoidal growth curve in for inrease in fruit size and dry weight of both species differs from the cyclic (double-sigmoidal) one described for typical drupes such as peach and cherry. The order of attainment of maximum size was fruit and endocarp (same time), seedcoat, and embryo, each separated by 1 week. By the time fruits turned ripe-red, the embryo had reached full size and become germinable. The endocarp was the last fruit component to reach physiological maturity, which coincided with the development of impermeability and a moisture content of < 15%. At this time, about 50%, 37%, and 13% of the dry weight of the drupe was allocated to the exocarp plus mesocarp unit, endocarp, and seed, respectively. This study lends support to the opinion of some plant taxonomists that Lobadium, of which R.aromatica is the type species, should be considered a subgenus of Rhus, rather than a distinct genus, as advocated as early as Rafinesque's time and defended by Barkley in 1965.

Key words: fruit, morphology, physiology, Rhus aromatica, Rhus glabra, seed