Answer:
Vascular plants are successful land plants. Spermatophyte (seed plants) is the largest group of vascular plants having two sub classes, angiosperms and gymnosperms. It include 300 families, 12500 genera and 300000 known species. The most successful and and important of these plants belong to Gramineae or the grass family with 7500 known species, which have colonized the great area of earth surface in particularly all sort of soil and climatic conditions and constitute the main source of man's food supply.
Factors responsible for success
1. Their adaptability to all kinds of environments.
2. The production of flowers, fruits and seeds, which show various adaptations for dispersal over large area.
3. These plants posses cuticle a thick cover around the epidermis which help in maintaining water or prevent dehydration.
4. Stomata are pesent in leaves or lenticle in stem which regulate the in and out of CO₂, O₂ and H₂O.
5. Well develop root system which help in absorption of mineral and other nutrients.