Corymb: It is a racemose inflorescence, here the main axis is comparatively short, and the the older flowers (lower flowers) have much longer pedicel then the upper ones (younger flowers). So all the flowers are brought to the same level.
Example: Cassia, Iberis, Caesalpinia
Umbel: It is a racemose inflorescence in which the peduncle is shorted. The pedicellate flowers arise from the tip of the peduncle in a centripetal succession. In the umbel there is an involucre of bracts seen at the apex of the peduncle.
Example: Hydrocotyl, Centella asiatica, Biophytum
Corymb vs Umbel
1. Peduncle is well developed.
2. The flowers arise at different levels from peduncle.
3. The pedicles of the older flowers are much more elongated as compared to those of younger flowers.
4. Arrangement of flowers is acropetal through from above it appears to be cetripetal*.
5. An involure is always absent. Bracts, if present, occur at various levels depending upon the origin of flowers.
1. Peduncle is reduced to a point.
2. All flowers radiate out from a common point.
3. There is a little difference in the pedicel length of different flowers.
4. Arrangement of flowers is centripetal.
5. An involure is often present at the place of origin of flowers.
*cetripetal:Flower development takes place from periphery to centre.