Answer:
1. High osmotic pressure due to the hypersaline nature of marine habitats
2. The dependence of flowering plants on pollinating insects for fertilization. These insect pollinators are however, absent in the marine environment.
3. Competition from already-established sea weeds and grasses provides another challenge to flowering plants invadingnthe oceans.
4. Constant changes in the environment as well as temperature changes too
Explanation:
The marine environment is a hypersaline environment with a high salt concentration relative to that of the plant cell. Due to high salt concentration of the marine environment, their is high osmotic pressure on living oragnisms found therein. Organisms must have well-adapted osmo-regulatory mechanisms to counteract the high osmotic pressure of their environment. Therefore, flowering plants face the challenge of removing excess salt from their cells or else lose water to their environment, hence resulting in the death of the plant. However, most flowering plants lack this ability and thus, have found it difficult to invade the oceans.
Flowering plants depends on insect-pollinators for fertilization. However, these insect are not found in the oceans, and as such, it is difficult for flowering plants to invade the oceans.
Well-adapted seaweeds and grasses serve as competitors for any invading flowering plant. Since the flowering plants are not yet adapted for life in marine habitats, they lose out in this competition.
The oceans are constantly in a state of frequent turbulence and change due to tides and currents. Also, the temperature of the oceans are very low and fluctuations in the temperatures of the ocean do occur, utimately serving as obstacles to invading flowering plants to adapt to life in the oceans and seas.
