Canopy structure of crops is an important factor determining the radiation environment of the canopy. Although many researchers have dealt with foliage distribution by using a probability density function, studies that reproduce a spatial destribution and spatial form of foliage in 3 dimensional (3D) space have only recently been reported. In this study, we developed a geometric model by using L-system to reproduce the form of sunflower plants in 3D space. The model consisits of frame and leaf models. In order to obtain functions to illustrate the frame model, positions of nodes, leaf bases, and leaf tips were measured from photographs of sunflower plants taken at five different stages in a growing season, and lengths of internode, petiole and leaf were determined. Moreover, lengths of five lateral veins, and divergence angle between midrib and fifth lateral vein were measured.
Growth curve of internode and petiole could be expressed as a logistic function of step number in L-system. Leaves elongated as a function of petiole length. Zenith angle of petiole decreased with step number from 1 to 7, and then stabilized at about 35°. Leaf zenith angle was related to petiole zenith angle. Divergence angles between successive leaves differed in different phyllotaxis. In distichous phyllotaxis, divergence angle was 180° between the leaves at the same node, and 90° between the leaves at successive nodes. On the other hand, in alternate phyllotaxis, divergence angle was about 135°. Leaf expansion could be related to increase in leaf length.
In conclusion, the geometric model using L-system successfully reproduced the growth of sunflower plants with increase in node number.
