Diagnostic key to five species of Dioscorea using micromorphological features

1. Phloem elements and cells of ground tissue are lignified; hilum and striations of starch grains are usually concentric:

2. Cortical sclerenchyma present, 1–2-layered; cortical parenchyma cells slightly lignified, devoid of starch grains; vascular bundles regular………………………… D. balcanica

2. Cortical sclerenchyma absent; cortical parenchyma cells non-lignified, containing small grains of starch; vascular bundles often irregularly anastomosing……………. D. villosa

1. Phloem elements and cells of ground tissue are non-lignified; hilum and striations of starch grains are usually eccentric:

3. Pericycle well-developed, 4–6-layered; pericyclic sclereids present; cells of ground tissue usually contain brown granular contents ………………………………………… D. rotundata

3. Pericycle undifferentiated; pericyclic sclereids absent; cells of ground tissue devoid of such brown granular contents:

4. Starch grains usually oval, semi-circular or elliptic, rounded at both ends; hilum radiating, cleft-shaped, or fissured; cluster crystals of calcium oxalate are rarely observed in the ground tissue………………………………… D. polystachya

4. Starch grains usually wedge-shaped, rounded at one end and straight at the other end; hilum dot-like; cluster crystals not observed ……………………………….………. D. bulbifera