Presence of plants organised into well defined vertical layers based on their heights can be best observed in

The correct option is tropical rain forest.

Step-by-Step Explanation:

1. Understanding Stratification:
Stratification refers to the vertical layering of a vegetation community, where different plants are organized into well-defined vertical layers based on their heights, growth habits, and light requirements. This structural complexity allows a large number of diverse species to coexist in the same area by partitioning resources like sunlight and space.

2. Comparing Ecosystems:
- Grasslands: These are dominated by grasses and herbaceous plants of relatively uniform, short heights. They generally have only one or two simple vertical layers.
- Tropical Savannahs: These consist of grasslands with scattered trees. While there is a canopy layer and a grass layer, the stratification is not highly complex or dense.
- Temperate Forests: These forests have distinct seasonal changes and moderate layering (typically consisting of a canopy, understory, shrub layer, and forest floor). However, the number of layers is limited compared to equatorial regions.
- Tropical Rain Forests: These forests receive high rainfall and abundant sunlight year-round, leading to rapid, dense, and diverse plant growth. This creates the most complex and distinct vertical stratification observed in any terrestrial biome.

3. Vertical Layers in a Tropical Rain Forest:
The vegetation is organized into five well-defined vertical layers:
- Emergent Layer: The tallest trees (ranging from 45 to 80 meters) that rise above the general canopy.
- Canopy Layer: A dense, continuous ceiling of tree crowns (around 30 to 45 meters) that absorbs the majority of sunlight.
- Understory Layer: Shorter trees and large-leaved shrubs (around 15 to 30 meters) adapted to low-light conditions.
- Shrub Layer: Low-lying woody plants and young saplings positioned below the understory.
- Forest Floor (Ground Layer): Comprising mosses, ferns, and decaying organic matter, receiving less than 2% of sunlight.

Therefore, the presence of plants organized into well-defined vertical layers based on their heights is best observed in a tropical rain forest.