Around the third week of December, the most outer region of the Arctic Circle receives barely two and half hours of sunlight and only six hours as January ends. The mid-arctic has no sun for three months starting the end of October, and right at the North Pole, there is no sun for six months starting the last week of September. For plants, which rely on sunlight for photosynthesis, this becomes an extremely harsh environment; however, the freezing arctic ocean adds to the difficulty of survival of arctic plants, leaving only a few that can overcome the obstacles.
Plankton are an aggregate of animals, as well as some plants. They normally drift in large groups both in salt and fresh water. Phytoplankton is the photosynthetic, or plant version, of plankton. There are about 70 dominant phytoplankton species found in the arctic seas.
They are vital to the ecosystem as they serve as food at the bottom of the food chain, fed on by slightly bigger organisms, such as copepods. Copepods are zooplanktons, or minute marine crustaceans, which normally possess six limb pairs on the thorax. Some are parasitic on fish. Another creature that feeds on phytoplankton despite it monstrous size is the humpbacked whale.
When much of the arctic ice melted during the last ice age about 18,000 years ago, about 150 new seaweed species—capable of living at low water temperatures and surviving prolonged periods of darkness—claimed the arctic seafloor. Most of these species, endemic to the arctic, grow at higher rate at such cold conditions than in more tropical ones. Examples of seaweed families include Furcellaria, Ceratocolax, and Halosacciocolax. Although arctic seaweed serves mainly as refuge to underwater animals rather than food, when it makes its way to shore during low tides, it serves as food to land animals such as the arctic hare and the polar fox.
One freshwater aquatic plant in the arctic is arctic moss, or Calliergon giganteum. This plant grows on the bottom of tundra lake beds and in and around bogs and fens. Normally, it is brown-colored with very tiny leaves and crowded branches. It is "the slowest growing, longest living freshwater macrophyte ever recorded” according to blueplanetbiomes.org. It grows as slow as one centimeter a year and lives a very long time; the shoots live seven to nine years and the leaves up to four.