Difference between Hypocotyl and Epicotyl

Main difference

The main difference between Hypocotyl and Epicotyl is that Hypocotyl is the region below the seed leaves (cotyledon), while Epicotyl is the region above the cotyledon of the stem.

Hypocotyl vs Epicotyl

The hypocotyl plays a role in epigeal germination in such a way as to ensure that the cotyledons come out of the soil, while the epicotyl has a role in hypogeal germination, which is responsible for keeping the cotyledons within the soil. The hypocotyl is found between the cotyledon node and the radicle (embryo root), while the epicotyl is found between the plumule (first shoot to grow from the embryo part of the seed) and the cotyledon node. Plumule is the terminal end of the Epicotyl, while the radicle is the terminal end of the hypocotyl.

Hypocotyl becomes a stem structure from which the root develops, while epicotyl becomes the stem structure, which bears leaves, fruits, and flowers. Hypocotyl growth starts from the radicle, while epicotyl growth starts from the cotyledon node.

The hypocotyl acts as the main elongation structure, which becomes the first part of the stem, which carries the flower, the fruit and the leaves. Epicotyl serves to lengthen the embryonic shoot from which true roots develop.

The hypocotyl cotyledons are green, so they exhibit photosynthetic activity; on the other hand, the cotyledons of the epicotile are not photosynthetic. The hypocotyl has cotyledons from the soil. The epicotile has cotyledons within the soil.

Comparative chart

Hypocotyl Epicotyl
The hypocotyl lies under the cotyledons of the embryo between the cotyledon node and the radicle. The epicotyl lies above the cotyledons between the plumule and the cotyledon node.
Germination type
Epigeal germination Hypogeal germination
Structures position
Under the seed sheets (cotyledons) of the embryo Above the cotyledon of the embryo
Termination point
At the cotyledonary point By plumule
Emergent point
From the radicle From the cotyledon node
Final developed structures
Initial part of the stem from which root development begins. The upper part of the stem has roots, stems, and leaves.
Plant germination
Above the ground Inside the ground
Photosynthetic characteristics of the cotyledon
Cotyledons are green and have photosynthetic characteristics. Do not exhibit photosynthetic characteristics
Cotyledon position
Off the ground Inside the ground

What is hypocotyl?

The hypocotyl is the region that extends through epigeal germination (in which a hook-shaped structure was also formed) towards a first part of the stem from which the root develops. The hypocotyl acts as the region between the cotyledon node (cotyledons can be monocots and dicots) and the radicle (a part of the root embryo). The radicle is the terminal end of the hypocotyl where its growth ends. Hypocotyl elongation is also affected by auxin (phytohormone) which induces rapid hypocotyl elongation. In monocotyledonous plants, the hypocotyl is not above ground because stem elongation is not characteristic of the monocotyledonous.

The hypocotyl portion is below the green cotyledons, so they are photosynthetic in nature. Hypocotyl growth is controlled by photomorphogenesis (development of the plant structure affected by light other than photosynthetic). Seedlings in the shade can give rise to the transcriptional response, negatively causing an increase in the growth rate of hypocotyl. If the plants are exposed to darkness, then the process called skotomorphogenesis occurs in contrast to photomorphogenesis.

In some species of plants, the hypocotyl can become enlarged, which is called a storage organ, and in some species it can grow above the ground. Examples of hypocotyl are Gloxinia and Cyclamen (its storage organ called a tuber), Celeriac.

Hypocotyl germinates through epigeal germination, which helps the cotyledons come out of the soil. The cotyledons of epigeal germination are outside the soil. Examples include beans, castor, cotton, papaya, onion, etc.

What is Epicotyl?

The epicotyl is the region above the cotyledon of the embryo in angiosperms. The epicotyl is present between the cotyledon node and the plumule. The epicotile is covered by coleoptile (protective sheath). The terminal point of the epicotyl is the plumule. Epicotyl serves to germinate within the soil below the soil. The epicotyle becomes the part of the stem, which is located above the ground, from which there are leaves, fruits and flowers. Epicotile elongation is controlled by phytochrome photoreceptors (a class of photoreceptors, which are sensitive to red and far red regions of light. Epicotyl cotyledons do not exhibit photosynthetic activity.

In dicot seeds, the epicotile is hooked and plumule in a downward direction. The plumule hook when it comes out of the abrasive ground, it is protected from damage.

Epicotyl germinates through hypogeal germination, which ensures that the cotyledons remain below the ground. The cotyledons of hypogeal germination are below the ground. Examples are peas, green beans, eutacta, mango, corn, rice.

Key differences

  1. The hypocotyl part of the germinating seedling is above the ground, while the epicotyl part is below the ground.
  2. The hypocotyl is found under the seed sheets of the embryo; on the other hand, the epicotyl is located above the cotyledons of the embryo.
  3. The hypocotyl is found between the plumule and the cotyledon node; on the other hand, the epicotyl is found between the plumule and the cotyledon node.
  4. Hypocotyl germinates through epigeal germination (role in plant development below ground), while epicotyl germinates through hypogeal germination (role in plant development above ground).
  5. The hypocotyl termination point is the cotyledonary node; conversely, the epicotyl termination point is plumule.
  6. Hypocotyl develops in the structure from which root development occurs, while epicotyl develops in the upper parts of the stem with flowers, fruits, and leaves.
  7. In epigeal germination, the hypocotyl spreads to remove the cotyledons; on the other hand, in hypogeal germination, the epicotyl spreads to keep the cotyledons in the soil.
  8. Hypocotyl cotyledons are photosynthetic because they are green, while epicotyl cotyledons are not photosynthetic.
  9. The cotyledon of the embryo is out of the soil in hypocotyl; on the other hand, the cotyledon of the embryo is within the soil in epicotyl.
Final Thought

The hypocotyl germinates through epigeal germination below the cotyledon, while the epicotile germinates through hypogeal germination above the cotyledon.

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