| S1 (Initiation) |
A ligule and a pair of auricles differentiate at the LJ initiation site |
No aerenchyma in LJ, which is full with parenchyma cells, except vascular bundles arranged at the abaxial side |
| LJ is hollow and transparent |
Small parenchyma cell clusters at the adaxial side and abaxial region between developing vascular bundles |
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The periphery of abaxial vascular bundles protrudes to form ridges |
| S2 (Young) |
LJ, leaf blade, and sheath are white or creamy yellow |
LJ size increases mainly due to the extensive expansion of parenchyma cells |
| LJ protrudes and becomes larger |
PCD of mature large parenchyma cells occurs to form small holes |
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Longitudinal holes connect and fuse to form intact aerenchyma |
| S3 (Young) |
Leaf continues to elongate, and leaf blade expands |
Rapid cell division between the vascular bundles and epidermis cells at the abaxial domain |
| LJ is still enclosed by the prior leaf sheath |
Small parenchyma cell clusters are formed at the adaxial side |
| Leaf blade and sheath become green, while LJ is white (distinguishable from each other) |
Parenchyma cells continue expanding |
| A pair of horn-shaped auricles and a tongue-like ligule can be observed |
Large and small vascular bundles locating at the abaxial side develop continuously |
| S4 (Maturation) |
Leaf blade and sheath fully develop |
Thickening of cell walls of small cell clusters results in the formation of sclerenchyma cell clusters |
| LJ emerges from prior leaf sheath and is exposed in the air |
Newly formed sclerenchyma cells at both sides perforate through longitudinally to form sclerenchyma fibers |
| LJ is firm and plump |
Vascular bundles and nearby wall-thickened small cell clusters at the adaxial side form ridges along the longitudinal direction |
| LJ starts to bend |
Parenchyma cells stop proliferation |
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The periphery of whole LJ becomes smooth and the transverse size of the LJ achieves its maximum |
| S5 (Postmaturation) |
LJ adaxial side elongates and bends to the abaxial side to form a curvature, resulting in the increasing leaf angle |
Ongoing thickening of cell walls of small cell clusters on both sides |
| Parenchyma cells at the adaxial side undergo longitudinal elongation |
| Asymmetric cell growth between the adaxial and abaxial sides leads to increased leaf inclination |
| S6 (Senescence) |
LJ approaches the maximum angle and begins to wither due to the loss of water |
Larger aerenchyma and fewer layers of parenchyma cells |
| LJ is dehydrated and distorted |
