THE ROTATED-LAMINA SYNDROME .3. CASES IN BEGONIA, CORYLUS, MAGNOLIA, PELLIONIA, PRUNUS, AND TILIA

The rotated-lamina syndrome occurs in all adult shoots of Tilia x europaea, and in lateral shoots of Corylus spp. and Prunus laurocerasus. Corylus and Prunus also have orthotropic radially symmetrical shoots that have normal leaf orientation. Development of the syndrome in leaf primordia in Tilia and Corylus is similar to that previously described in Ulmus, i.e., the leaf primordium is initially asymmetrical so that the leaf blade component of the primordium arises facing only obliquely towards the shoot apex, and further asymmetrical outgrowth of the leaf buttress brings the leaf blade region into the rotated position. Leaves of Begonia foliosa and the ventral leaves of (anisophyllous) Pellionia pulchra arise from initially symmetrical primordia, and lamina rotation occurs by asymmetric growth at the base of die leaf blade region. The process is similar to that in the woody examples but occurs at a proportionately later stage of leaf development. Development of the syndrome in Prunis laurocerasus and Magnolia x soulangeana differs considerably. Primordia are slightly asymmetrical but have normal dorsiventrality at first, but when the lamina arises the two edges of the leaf blade grow towards the same (upper) side of the bud, and this is responsible for most of the appearance of rotation. In general the upper stipule is initially larger than the lower and arises much earlier in Corylus and Tilia. Leaves that have normal orientation in Corylus and Prunus develop from quite symmetrical primordia, but those of Corylus may show some asymmetry of stipule development. Shoots of all cases can be considered to show heteroblastic growth, and the early part of the heteroblastic sequence is prolonged in the orthotropic shoots with normally oriented leaves in Corylus and Prunus. The morphological and morphogenetic significance of the rotated-lamina syndrome is discussed.