Cycas called living fossils

Cycas are plants of the Cycadales class. Plants of the Cycadales class are called Cycads. Cycads were widespread throughout the world during the Mesozoic Era. Later they disappeared. Today they are found as fossils. 100 species of 9 genera including Cycas in the Cycadales class are still alive on Earth. Characteristics of present-day living Cycas are found to closely match those of fossil Cycads of the past. Hence Cycas are called living fossils.

Cycas Leaves

Cycas have two types of leaves at the top of the stem. Leaflets and invoices.
(i) Leaves or Compound: Leaves are simple, green, smooth, large and pinnately compound. It is spirally arranged at the tip of the stem and forms a crown-like structure. Rackets contain 50-100 pairs or 100-200 leaflets. The leaves are obtuse, thick and leathery. Its length is 1.0-2.7 m. The mature leaves have a midvein, the veins and subveins are indistinct. Immature and young leaves are coiled like ferns. This condition is called sarcinate vernation.
(ii) Sepals: Sepals are small and covered with brown hairs. It is alternately furnished with foliage. It covers the bud of compound leaves.
Cycas leaves have some similarities with the leaves of palm plants and ferns. Hence Cycas is called pumpfern.

Cycas Root

The main root of Cycas is transient. Abdominal roots are formed after the main root is destroyed. Abdominal roots grow underground. Some parts of the adventitious root emerge above the soil and bifurcate to form branches. Above ground these root bacteria are attacked by Nostoc, Anabaena etc. The normal shape of these affected roots changes and becomes deformed. Because the distorted shape of the root resembles that of sea coral or coral, they are called coralloid roots or coral roots or root tubercles. The part of the cortex of the coralloid root where Nostoc and Anabina reside is called the algal layer.

Cycas-structure

1. Root: The main root of Cycas is transient. Abdominal roots are formed after the main root is destroyed. Abdominal roots grow underground. Some parts of the adventitious root emerge above the soil and bifurcate to form branches. Above ground these root bacteria are attacked by Nostoc, Anabaena etc. The normal shape of these affected roots changes and becomes deformed. Because the distorted shape of the root resembles that of sea coral or coral, they are called coralloid roots or coral roots or root tubercles. The part of the cortex of the coralloid root where Nostoc and Anabina reside is called the algal layer.
2. Stem: The stem of Cycas is straight, long, sessile, stout and cylindrical. It grows up to 8-14 feet tall. Some species are even taller. When the apex of the stem breaks, the stem becomes branched. It is covered with temporary leaves like armor. It has a permanent leaf scar.
3. Leaves: Cycas have two types of leaves at the top of the stem. Leaflets and invoices.
(i) Leaves or Compound: Leaves are simple, green, smooth, large and pinnately compound. It is spirally arranged at the tip of the stem and forms a crown-like structure. Rackets contain 50-100 pairs or 100-200 leaflets. The leaves are obtuse, thick and leathery. Its length is 1.0-2.7 m. The mature leaves have a midvein, the veins and subveins are indistinct. Immature and young leaves are coiled like ferns. This condition is called sarcinate vernation.
(ii) Sepals: Sepals are small and covered with brown hairs. It is alternately furnished with foliage. It covers the bud of compound leaves.
Cycas leaves have some similarities with the leaves of palm plants and ferns. Hence Cycas is called pumpfern.

Cycas-Identifying characteristics

1. Cycas are sporophyte plants. Its body can be divided into roots, stems and leaves.
2. They are erect palm-like plants.
3. They have brown hairy bracts and green foliage.
4. The green leaves are large, pinnately compound and spirally arranged.
5. Young leaves have sarcinate vernation or whorls.
6. Their leaves contain transfusion tissue.
7. Stems are straight, sessile, stout, cylindrical and with persistent petioles.
8. They have seeds, no fruit and the seeds are naked.
9. Germs form strobilus.
10. Their ovules are large, unencapsulated and located in the endosperm.
11. They are heterosporic or uninucleate.
12. They are air pollinated. That is, pollination takes place through air.
13. They have coralloid roots.
14. Their spermatozoa are the largest, Latim-like, multi-flagellated and motile. Dr. Siddique Publications
15. Their sexual reproduction is ogamous in nature.
16. Their embryos are created.
17. They are archegonoids.

Cycas-Geographical Distribution

15-20 species of Cycas are found all over the world. However, the distribution of Cycas is more noticeable in high and sub-tropical regions. Cycas grows abundantly in East Africa, India, South China, Japan, Madagascar, Australia, etc. Cycas grow in the hilly areas of Chittagong and the Ghazni forests of Sherpur in Bangladesh. Cycas revoluta and Cycas circinalis are planted in gardens as ornamental plants.