THE ROTATED-LAMINA SYNDROME .5. PARTIAL LAMINA ROTATION AND RELATED FEATURES IN HAMAMELIDACEAE

Shoots of Hamamelidaceae have been examined for the presence of the ro tated-lamina syndrome, a condition in which young leaves in bud face t owards one side of the shoot (normally the upper) rather than towards their own shoot apex. Early leaf development and bud organisation have been examined in representatives of eight genera with dorsiventral sh oots and distichous phyllotaxis, and of four genera with radially symm etrical shoots and spiral or decussate phyllotaxis. Radially symmetric al shoots do not show any evidence of the syndrome. The distichous Cor ylopsis and Hamamelis species studied have leaf primordia that are asy mmetrical from an early stage and show partial lamina rotation, the la mina facing obliquely towards the upper side of the bud. Mature lamina e are usually asymmetrical. In Corylopsis rotation arises by torsion i n the petiole region, and in Hamamelis by asymmetrical growth of the l eaf base. Distichous examples without lamina rotation also have asymme trical primordia in most cases, often have asymmetrical leaves, and al l show the same asymmetrical development of the leaf base as found in Hamamelis. It is suggested that these features represent either (i) re lies of rotated-lamina syndrome that was present in these cases but ha s been suppressed or (ii) early stages in evolution of rotated-lamina syndrome. It is suggested that suppression is the more likely interpre tation. Corylopsis and Hamamelis may also be in the process of suppres sing the syndrome.