Adenium "obesum" x swazicum hybrids
Adenium "obesum" x swazcium hybrids are probably the first intergeneric crosses made in the genus. The primary hybrids (first generation, aka F1) have fairly consistent traits and are usually quite beautiful. The plants are well-branched shrubs, but usually with weak stems that need hard pruning to maintain a neat, upright form. The swazicum parent often contributes a large caudex or swollen roots. The “obesum” parent contributes large flower size and a wide range of colors. The swazicum parent intensifies the flower color (if the parents are dark) and transmits uniform petal color (i.e., it doesn’t fade toward the throat as in all other species except A. boehmianum). F1 hybrids also have dark red or black throats. The primary hybrids are pollen-sterile, so second generation (F2) crosses are not possible. F1 plants can be used as seed parents and back-crossed to one of the parent species, but most offspring are weak. Because of these problems, complex A. swazicum hybrids (second generation and beyond) are rare. See the superior cultivar page for a gallery of the best.
Above left: a flower of 'Crimson Star' (bottom) with its parents A. "obesum" 'Red Everbloomer' (left) and A. swazicum 'Boyce Thompson'. This old scanned transparency is oversaturated. The photo above right is closer to 'Crimson Star's' color. Notice the centripetal fading of the petals of the "obesum" parent, and the solid color and characteristic dark throat of the hybrid.
A 10-year-old cutting-grown 'Crimson Star'. This cv. has thick, sturdy stems and roots, but they develop slowly.