Epiphytes
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Epiphytes are autotrophic plants that grow on the surfaces of other plants, absorbing moisture and nutrients from the atmosphere and decaying supporting plant material. They exhibit various morphological and anatomical adaptations, such as specialized root systems and modified leaves, to thrive in diverse environments, particularly rich in moist, warm regions. Types of epiphytes include protoepiphytes, hemiepiphytes, nest epiphytes, and tank epiphytes, each with unique characteristics in water and nutrient acquisition.
Epiphytes
- 1. Epiphytes Dr. Ravindra. D. Madhekar Assistant professor, Department of Botany, S. B. E. S. College of Science, Aurangabad (Maharashtra) India
- 2. • Epiphytes (Epi = above, phyton = plant) • Those autotrophic plants which grow on the surface of some other supporting plants and are not permanently rooted in the soil. • Absorb sufficient moisture from the atmosphere and mineral nutrients from the decaying bark of the supporting plants upon which they are situated. • Differ from parasites and also from lianas (woody stem climbers). • Also called Aerophytes or air plants.
- 3. • Distribution: • Grow on the surface of submerged aquatic plants, may be aerial, on the surface of tree trunks, grow even on the surface of leaves (i.e., epiphyllous epiphytes). • Epiphytic vegetation is very rich in moist and cold regions but poor in dry and cold areas. • In north-western Himalayas much less in number as compared to those present in the eastern Himalayas. • In warm and wet regions, members of the families Bromeliaceae and Orchidaceae are found in abundance. • In tropical rain forests, epiphytic species found at the tops of trees are xerophytic in nature but those occurring at lower levels are hygrophilous (moisture and shade loving).
- 4. Morphological adaptations (i) Root system: • Extensively developed. • The roots may be of the following three types (a) Normal absorbing roots (b) Clinging roots (c) Aerial roots
- 5. (ii) Stem: • May or may not be extensively developed. • Some epiphytes develop succulence in their stems and become pseudo-bulbous or tuberous (iii) Leaves: • Considerable reduction in leaf number. • Some orchids develop only a single leaf in a growing season. • Leaves in some may be fleshy and leathery • In Dischidia nummularia, Platycehum and Aspleniumnidus leaves are modified into the pitchers.
- 6. • Dischidia nummularia, (Asclepiadaceae), shows peculiar types of leaf pitchers. In family Bromiliaceae, some species develop spoon-like leaves in rosettes. (iv) Fruits, Seeds and their dispersal: Usually dispersed by wind, insects and birds.
- 7. Anatomical adaptations (i) Presence of thick cuticle and sunken stomata: • These two structures greatly reduce the loss of water from the plants. • Generally the surface cells of water absorbing organs (roots and some leaves) are not cuticularized. • In succulent epiphytes, thin-walled parenchymatous tissue that stores water develops extensively. • The aerial hanging roots of many tropical epiphytes belonging to the families Araceae and Orchidaceae develop on their surface a characteristic greenish white thin-walled massive tissue called as velamen
- 8. • The velamen is hygroscopic tissue that rapidly absorbs moisture from the saturated atmosphere like a sponge. • It is modification of multilayered epidermis. • Its cells are empty (i.e., dead) and cell walls show spiral or reticulate thickenings. • Inner to the velamen there is present a peculiar layer called exodermis.
- 9. • Exodermal cells are of two types: • (a) Lignified and thick walled cells. • (b) Thin-walled cells or passage cells, walls of which are permeable to water. The velamen absorbs and retains moisture till that is absorbed by passage cells of exodermis. • (iv) Other structures are similar to those found in mesophytes.
- 10. • Types of Epiphytes: (1) Protoepiphytes: Derive their nourishment partly from the surface of the supporting plants and partly from the atmosphere. Examples: Peperomia, Dischidia and some ferns belong to this group. (2) Hemiepiphytes: • Grow on the supporting plants in the beginning like true epiphytes but later on they establish connection with the soil by their roots. • Some grow in the soil but their stems die from below upward and terminal portions live independently like hemiepiphytes. (Pseudoepiphytes).
- 11. (3) Nest epiphytes: • These have appropriate devices to collect large quantity of water and humus for their own use. E. g Orchids (4) Tank epiphytes: • These plants develop fibrous anchoring roots which do not take part in the water absorption. Leaves, that are variously modified, absorb water and manufacture food. • Nidularium, Tillandsia, and other epiphytic species of Bromeliaceae are common plants of this group.