A newly found leaf arrangement to reduce self-shading was observed in a Japanese warm-temperate forest. For monoaxial trees that deploy leaves directly on a single stem, leaf arrangements involving progressive elongation of the petiole and progressive increase in deflection angle (the angle between stem and petiole) from the uppermost to the lowermost leaves act to reduce self-shading. However, the progressive reduction in petiole length and deflection angle from the uppermost to the lowermost leaves should also result in the reduction of self-shading. Nevertheless, the latter leaf arrangement has not been reported previously for any tree species. Four Araliaceae species, namely, Gamblea innovans, Chengiopanax sciadophylloides, Dendropanax trifidus and Fatsia japonica, which are typical monoaxial tree species in Japan, were studied. We examined the crown structure of saplings growing in the light-limited understorey in a Japanese warm-temperate forest. Two evergreen species, Dendropanax trifidus and F. japonica showed progressive petiole elongation and progressive increase in the deflection angle from the uppermost to the lowermost leaves. In contrast, saplings of deciduous species, G. innovans and C. sciadophylloides had a leaf arrangement involving progressive reduction in petiole length and deflection angle from the uppermost to the lowermost leaves. The leaf arrangement has diversified among members of the same family, but all four studied species develop a crown with little self-shading that is adapted for growth in the light-limited understorey. Although trees are likely to be under the same selective pressure to reduce self-shading, this study revealed that there is flexibility in its morphological realisation, which has been poorly appreciated previously.

在日本暖温带森林中观察到一种新发现的减少自荫的叶子排列。对于直接在单个茎上展开叶子的单轴树木，叶子排列涉及从最上面的叶子到最下面的叶子逐渐伸长叶柄和逐渐增加偏转角（茎和叶柄之间的角度），以减少自遮光。然而，从最上面的叶子到最下面的叶子，叶柄长度和偏转角度的逐渐减少也会导致自遮光的减少。然而，此前没有任何树种报道过后一种叶子排列方式。对日本典型的单轴树种五加科植物Gamblea innovans、Chengiopanax sciadophylloides、Dendropanax trifidus和Fatsia japonica四种树种进行了研究。我们检查了在日本暖温带森林中光照有限的林下生长的树苗的树冠结构。两种常绿植物，三裂树和日本竹，从最上面的叶子到最下面的叶子，叶柄逐渐伸长，偏转角度逐渐增加。相比之下，落叶树种的树苗，G. innovans和C. sciadophylloides的叶子排列涉及从最上面的叶子到最下面的叶子，叶柄长度和偏转角度逐渐减小。同一科成员的叶子排列方式有所不同，但所有四个研究物种都形成了几乎没有自遮荫的树冠，适合在光线有限的下层植物中生长。尽管树木可能面临同样的选择压力来减少自荫，但这项研究表明，其形态实现具有灵活性，而这一点以前并未得到充分认识。