Morphological and ontogenetic studies on southern African podocarps. Shoot apex morphology and ovuliferous cone initiation

Four species of Podocarpus indigenous to southern Africa were investigated. The morphology of the primordium of the female cone is compared with that of the shoot apex. Rhythmic growth occurs in Podocarpus. The external morphology of bud scales protecting dormant shoot apices is described and illustrated. Female strobili of the three species of section Podocarpus studied are initiated in the axils of euphylls during the spring growth flush as laterally flattened triangular structures. The axillary position of a female cone indicates that it is a modified shoot. The first two cone bracts (prophylls) are formed approximately at right angles to the subtending bract (one or both are fertile), while the 3rd and 4th bracts originate on the anterior and posterior sides of the strobilus respectively. Two to four bracts per cone are formed, not in pairs–the phyllotaxis is spiral. In P.falcatus primordia of female strobili and vegetative branches could be distinguished only after emergence of the seed scale complex. Based on cell differentiation, well-defined cytological zones can be distinguished in the shoot apex and it is classified as being of the Abies-Cryptomeria-lype. Meristematic zones of cone primordia and vegetative branches are basically similar, although the former are less well defined. No gradual transition from a vegetative to a reproductive apex could be identified and it would seem that the fate of axillary buds are determined at the time of their origination or even before.