Cladonia rangiferina

Cladonia rangiferina is a unique type of organism known as a fruticose lichen.

While many people call it reindeer moss or caribou moss, it is not actually a moss. Instead, it is a lichen, which is a partnership between two different life forms. This specific species is often called reindeer lichen or grey reindeer lichen. It is extremely important to ecosystems because it serves as a vital food source for reindeer and caribou.

Because it supports these large animals, the lichen has significant economic importance in many regions.

A lichen is formed by a symbiotic relationship between a fungus and an alga. In the case of Cladonia rangiferina, the fungal partner works with an alga called Trebouxia irregularis. Scientists study how these two join through a process called lichenization. This process happens in several distinct stages. First is the pre-contact stage, which occurs about one day after the partners are introduced. During this time, there is no visible growth. By the eighth day, the contact stage begins. Here, fungal hyphae—tiny thread-like structures—grow toward the algal cells. They may form swollen tips called appressoria to make contact. By 21 days, the growth together stage occurs. The algal cells become integrated into a network within the fungal matrix.

This lichen has a very specific physical structure. It is fruticose, meaning it has a bushy, branched shape. The branches usually divide into two, three, or four smaller parts. The color of the lichen can range from greyish to whitish or even brownish grey. It forms large, extensive mats on the ground. Unlike some other species, it lacks a thick, protective outer layer called a cortex. Instead, a loose layer of hyphae covers the photobionts, which are the light-capturing algal cells. When the lichen is fertile, its tips may split into small, umbrella-shaped clusters.

These clusters hold tiny reproductive discs called apothecia, which are often hidden just below the growing tips.

The history of our scientific understanding of this lichen began in the 18th century. Carl Linnaeus first described the species in his 1753 work, Species Plantarum. At that time, he placed it in his own genus and named it Lichen rangiferinus. In 1780, Friedrich Heinrich Wiggers moved the species to the genus Cladonia. This change gave us the modern scientific name we use today. Since then, researchers have looked closely at its complex chemistry. They have found many bioactive compounds, such as atranorin and fumarprotocetraric acid. Some of these substances have shown the ability to inhibit certain bacteria, like methicillin-resistant Staphylococcus aureus.

Cladonia rangiferina is famous for being incredibly tough and able to survive extreme stress. It can live in both hot and cold climates, often dominating the ground in boreal pine forests and alpine tundra. The lichen can survive temperatures as low as -40°C. It can even continue to breathe after being immersed in liquid nitrogen. It is also highly resistant to dehydration and high salinity. However, its strength is balanced by its very slow growth rate. It typically grows only between 3.9 and 4.4 mm per year. Because it grows so slowly, it may take many decades to recover if it is burned, trampled, or overgrazed.

Different environments change how the lichen grows and reproduces. In humid areas with plenty of water, the lichen often grows taller, reaching about 12 cm. These moist sites also tend to produce more fertile apothecia. In drier locations, the lichen is much shorter, often only 4 to 6 cm tall. The lichen is also a polycarpic species, meaning it can produce sexual spores throughout its 20-to-30-year lifespan. These spores help the lichen spread over long distances. In some parts of the world, like the British Duchy of Cornwall, this lichen is considered an endangered species and receives special protection.

Humans have found many ways to use reindeer lichen throughout history. The Inland Dena'ina people have used it as a food source by boiling or soaking it. They sometimes mix the soft lichen with berries, fish eggs, or lard. It is also a source of vitamin D. In the West Kameng district of the Eastern Himalaya, the Monpa people use it as a traditional remedy for kidney stones. Some cultures even use it to make a drink called aquavit or as decoration for glass windows. However, because of the acids in the lichen, it must be cooked well to avoid an upset stomach.