Category: Biology Second Paper Lecture Sheet

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.

Cycas are perennial, tall, bushy, evergreen and gymnosperms. Cycas look a lot like palm trees or ferns so they are called pumpferns. They grow in dry places on mountains. It grows in plains. They grow well in hot and humid climates. Cycas are believed to have originated 30 million years ago

Kingdom : Plantae
Division : Cycadophyta
Class : Cycadopsida
Order: Cycadales
Family: Cycadaceae
Genus: Cycas
Species : Cycas pectinata

1. Sequoia sempervirens: Sequoia sempervirens is a gymnosperm. Its height is 115.92 meters or 380.3 feet. Redwood National Park, California, USA.
2. Shorea faguetiana: Shorea faguetiana is an herbaceous plant. Its height is 100.8 meters or 331 feet. Borneo, Indonesia, Asia.
3. Eucalyptus regnans: Eucalyptus regnans is an herbaceous plant. Its height is 99.82 meters or 329.7 feet. Tasmania, Australia.

The leaves of gymnosperms have special markings on the stems when they fall in a storm. This special mark is called leaf scar. Leaf scar is a heterogeneous feature of gymnosperms.

1. Gymnosperms are green, autophagous and evergreen.
2. The main plants are sporophytes and shoots.
3. Their body is divided into roots, stems and leaves.
4. They have two types of leaves. Brown bracts and green foliage.
5. Their leaves are pointed (Pine) and compound type (Cycas).
6. The plant has leaf scars.
7. Their flowers are simple and unisexual.
8. Flowers have microsporophylls or spores and megasporophylls or spores.
9. Their flowers do not have uterus, uterus and uterus.
10. During pollination, the pollen grains fall directly into the ovule opening.
11. As the flower does not have a uterus, the fruit does not form.
12. As the fruit does not develop, the seeds are naked or expressed.
13. Their seeds are haploid and formed before fertilization.
14. Their seeds germinate to form diploid sporophyte plants.
15. They do not become double-toxic (Ephedra does).
16. The number of cotyledons in their embryos is one, two (Cycas) or more (Pinus).
17. They are air pollinated. That is, pollination occurs through wind.
18. Vascular bundles are free, parallel and annular.
19. Xylem does not contain vessel cells (Gnetum does) and phloem lacks companion cells.
20. They are archegoniates. That is, archegonia create.
21. They are heterosporous. That is, two or more types of spores are produced.
22. Most of their species are terrestrial and tropical.
23. Asymmetric or heteromorphic genes exist in the life cycle.

There are about 70 species in the Gnetophyta division. They have most similarities with herbaceous plants. Their leaves are similar to herbaceous plants. They have vessels in their xylem and spermatozoa are without flagella. The Welwitschia plant has two leaves and flower-like pods (Welwitschia is found in the Namibian desert). Double fertilization occurs in Ephedra plants of this category. The respiratory medicine ephedrine is obtained from the Ephedra plant.

Coniferophyta contains 550 species in 6 families. The temperate Northern Hemisphere has conifer forests. Russia has conifer forests. The world’s largest conifer forest is located in Siberia and is the world’s largest biome. Bristlecone pine is the oldest tree in the world. Its age is 5000 years. It is found in Navana and California. The tallest trees in the world are Hyperion (Sequoia sempervirens) at ± 400 feet and Coast Redwood (Sequoia gigantea) at 324 feet.

Plants of Cycadophyta division are called cycads. This 200 million year old division survives today with 100 species. They are woody plants like palm trees. Their leaves resemble leathery feathers. Their sperm have flagella. They are widespread in the equatorial region. They grow in dry arid and wet wetlands. The division Cycadophyta consists of three classes. Cycadofilicales, Bennettitales and Cycadales. Zamia pygmaea cycad is the smallest gymnosperm plant in the world. Dr. Siddique Publications

Ginkgo biloba is the only living species of Ginkgophyta. It is the world’s oldest seed plant that has survived on Earth with little change. Their leaves are large and fan-like. Their sperm are flagellated and motile. These plants greatly pollute the environment. They are disease and insect resistant.