Pinus - Description, Life Cycle and Examples

What is Pinus?

Pinus is a genus of the family Pinaceae. Any conifer of this genus is termed as Pine. They are mostly trees and rarely shrubs. Furthermore, they are a long-lived variety of plants. The Pinus genus can be subclassified into yellow pines, white pines and lacebark pines.

The pines are monoecious plants, and thus, the female cones and male cones are seen on the same tree.

Classification of Pinus

Pinus (Genus) – Description

The Pinus are resinous evergreen trees. They are mostly described based on their cones, needle and barks.

• Pinus Needle – The adult pine leaves are called needles. The foliages are bundled together in clusters known as fascicles.
• Cone – Cones are seed-bearing structures seen in gymnosperms. Usually, the female pine cones are larger compared to the male pine cones. They are encircled with many scales. Typically, the scales at the tip and base of the cone are sterile (no seeds).
• The seeds are winged structures that can be dispersed through the wind.
• The white pines (Strobus) have leaves in clusters of five. Their wood is generally soft and white with less prominent annual rings. They are called soft pines or haploxylon. E.g., P. gerardiana.
• The yellow pines (Pinus) have thick and fissured bark. Their wood is harder and yellower, with more prominent annual rings. They are called hard pines or diploxylon. E.g., P. roxburghii.
• The lacebark pines (Ducampinus) are an ancient group of pines with diverse morphology. This third subgenus is no longer considered valid.

Distribution of Conifers

The humid temperate northern part is dominated by the Pinaceae and other conifers, and the southern part has more ferns and conifers other than the Pinaceae. Some varieties of Pinus have also been introduced in the temperate parts of the southern hemisphere.

Some Examples of Pinus Species

• Pinus brutia
• P. densata
• P. henryi
• P. roxburghii
• P. greggii
• P. radiata
• P. gerardiana
• P. rigida

Life Cycle of Pinus

Pinus are gymnosperms that produce seeds in cones. Their ovules are not enclosed by any ovary wall and thus remain exposed before as well as after fertilisation.

Seed plants have a diplohaplontic life cycle that has two phases. The first dominant is the sporophyte phase, and the second is a brief gametophyte phase. Pines are monoecious; thus have female and male strobili are present on the same tree.

Male Strobili

• A male strobilus has many microsporophylls. Each of them has two microsporangium sacs.
• Each sac has tapetal pollen mother cells. These cells undergo meiosis to form 4 haploid microspores in the tetrad.
• The microspore coated with a pollen wall divides into a male gametophyte. Each male gametophyte produces two sperms for fertilisation.

Female Strobili

• Likewise, the female strobilus has many scales that produce megasporangia or ovules. Each ovule includes a megaspore mother cell that undergoes meiosis to produce 4 haploid cells.
• One of the four haploid cells grows into a female gametophyte that develops one or more archegonia. Each archegonium houses a single egg cell.

Fertilisation – The mature sperm cells reach down the pollen tube and fertilise the egg. After fertilisation, the integuments close to form a seed coat. The development of the embryo happens within the seed. Under favourable conditions, the seed germinates into a full sporophyte plant and continues the life cycle.

Also, Check: Difference between Cycas and Pinus

Explore: NEET MCQs on Pinus

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