Because of the many common traits plants and green algae share, we know that plant life began in the water and adapted to land. Some of the traits they share:
- both are photosynthetic eukaryote
- both have the same types of chlorophyll
- both use starch as a storage product
- both have cell walls with cellulose
Plants have adaptations that allow them to live on land such as the ability to retain moisture, transport water and other resources between plant parts, grow upright, and reproduce without free-standing water.
Retaining moisture - plants have a cuticle which is a waxy waterproof layer that holds in moisture. The cuticle has tiny holes, stomata, in it that allow air to move in and out of the plant.
Transporting Resources - some plants have developed a vascular system which allows them to move resources to different parts of the plant. Think of the vascular system as a plumbing system. The vascular system brings in water and minerals from the roots, and carry food (sugar) from the leaves to other parts of the plant.
Growing upright - plants need structure to support their weight. This comes from ligin, a carbohydrate, that hardens cell walls of some of the vascular tissue. It also provides a stiffness to the stems. Ligin also waterproofs the tissues, making them more efficient at transporting fluids.
Reproducing on Land - eggs are fertilized in the parent plant, but early plants (non-vascular) still required water for this to happen. Seed plants (an adaptation) have made this much easier. Pollen and seeds are adaptations that allow seed plants to reproduce without water. Pollen grains contain a cell that divides to form sperm. The pollen can then be carried by wind or animals to the female plant structure. Seeds are a storage device for a plant embryo. Seed coats protect the embryos from drying out in wind and sunlight, the embryo then develops when the environment is favorable.
Plants have coevolved with other organisms in their environment. Over time plants have developed mutualisms or relationships that benefit both organisms. Examples are bacteria and fungi that live near plant roots and help provide plants with nutrients, while the plant roots provide the bacteria and fungi with a habitat. Another example is flowering plants and their animal pollinators, the plants depend on the animals for pollination and the animal feeds on the plants.
Watch the Plant Evolution video from Nottingham Science.