What is the Difference Between Crustose Foliose and Fruticose Lichens

The key difference between crustose foliose and fruticose lichens is that crustose lichens have a crust-like appearance, while foliose lichens have a leaf-like appearance, and fruticose lichens have a branching bush-like appearance.

Lichens are a group of symbiotic forms that results from a symbiotic association between heterotrophic fungi and photosynthetic algae. They are known as composite organisms. They have varying characteristics to their individual parent organisms. They have many beneficial roles, such as acting as indicator organisms, production of important secondary metabolites, and acting as a food source for herbivores. Crustose, foliose, and fruticose are three forms of lichens based on their appearance or shape of the thallus structure.

CONTENTS

1. Overview and Key Difference
2. What are Crustose Lichens
3. What are Foliose Lichens
4. What is Fruticose Lichens
5. Similarities – Crustose Foliose and Fruticose Lichens
6. Crustose vs Foliose vs Fruticose Lichens in Tabular Form
7. Summary – Crustose vs Foliose vs Fruticose Lichens

What are Crustose Lichens?

Crustose lichens are a type of lichen that takes a crust-like appearance during its growth phase. These lichens strongly attach to the solid substrate, giving it a hard appearance. This is also characterized by the branching cracks present in the crust of the lichen. The crust-like lichens may also appear thick and lumpy based on the growth rate of the lichen. The basic structure of the crustose lichens comprises a cortex, algal layer, and medulla. The thallus structure of the crustose lichens appears scattered and granulated. The texture of them often appears smooth, but based on the presence of the cracks, the texture may vary.

Crustose lichens can be found in many habitats, such as epiphytic algae and liverworts, living leaf surfaces, or carbonate-rich karst areas. Their growth rate is 0.5 mm per year, and has a lifespan of 500 – 5000 years. Crustose lichens are mainly involved in weathering of rocks and also take part in the corrosion of carbonate rocks. Lecanora garovagli and Pleopsidium chlorophanum are examples of crustose lichens.

What are Foliose Lichens?

Foliose lichens are another type of symbiotic association between fungi and algae, and they take the appearance of a leaf and have a thallus composed of hyphae-like root structures. The characteristic thallus structure has a flattened surface containing an upper and a lower cortex. They live in a variety of environments and show a slow growth rate of less than 1mm per year. The average lifespan of a foliose lichen is between 30 – 60 years. The foliose lichens facilitate attachment to the surface through the root-like structures that are called rhizines.

The main function of foliose lichens is that they act as strong indicators of atmospheric pollution. In addition, they are a good source of food for herbivorous animals such as deer and goats. Pseudocyphellaria rainierensis is an example of a foliose lichen.

What are Fruticose Lichens?

Fruticose lichen is a symbiotic relationship between fungi and algae and takes the shape of a branching bush. This is the most diverse group of lichens. They have a very complex vegetative structure that does not have true leaves, stems, or roots. The specialty of fruticose lichen is that the color of the lichen alters with the amount of light and water. A light-colored thallus is associated with low light conditions and vice versa. They also live in a wide spectrum of environments.

The growth rate of fruticose lichen is greater than 2 mm per year. The average lifespan of a fruticose lichen is over 100 years. Cladonia fimbriata and Usnea longissimi are examples of fruticose lichens.

What are the Similarities Between Crustose Foliose and Fruticose Lichens?

• Crustose, foliose, and fruticose lichens form as a result of a symbiotic association.
• The symbiotic association of all three forms is between fungi and photosynthetic algae.
• All forms can be found in varying habitats.
• They form thallus structures.
• Moreover, all three types do not bear true roots, stems, or leaves.
• All forms are photosynthetic.
• Crustose, foliose, and fruticose lichens are dependent on water for reproduction.
• They are important environmental pollution indicators.
• They are important forms of food for herbivorous animals.
• All three forms of algae produce important secondary metabolites.

What is the Difference Between Crustose Foliose and Fruticose Lichens?

Crustose lichens take a crust-like appearance, foliose lichens take a leaf-like appearance, and fruticose lichens take a branching bush-like appearance. Thus, this is the key difference between crustose foliose and fruticose lichens. The growth rate of crustose lichens is 0.5 mm per year, while foliose lichens have a growth rate of less than 1 mm per year and fruticose lichens have a higher growth rate of more than 2 mm per year. Moreover, the lifespan of crustose lichens varies from 500 – 5000 years, while that of foliose lichens varies from 30 – 60 years and fruticose lichens have a lifespan of over 100 years.

The below infographic presents the differences between crustose foliose and fruticose lichens in tabular form for side-by-side comparison.

Summary – Crustose vs Foliose vs Fruticose Lichens

Lichens are composite organisms that arise due to a symbiotic relationship between fungi and algae. Based on the appearance of their thallus structures, there are three types of lichens. They are crustose lichens, foliose lichens, and fruticose lichens.Crustose lichens take a crust-like appearance. Foliose lichens take a leaf-like appearance, while fruticose lichens take a branching bush-like appearance. So, this is the key difference between crustose foliose and fruticose lichens. All of them exist in a variety of environments; however, they vary in their growth rates and lifespan. They produce important secondary metabolites and act as indicators of environmental pollution.

Reference:

1. Grimm, Maria, et al. “The Lichens’ Microbiota, Still a Mystery?” Frontiers in Microbiology, U.S. National Library of Medicine, 30 Mar. 2021.
2. “Lichen Biology.” U.S. Forest Service. Forest Service Shield.

Image Courtesy:

1. “Crustose lichen” By sanjay_ach – Own work (CC BY 4.0) via Commons Wikimedia
2. “Flavoparmelia caperata – lichen – Caperatflechte” By Norbert Nagel, Mörfelden-Walldorf, Germany – Own work, (CC BY-SA 3.0) via Commons Wikimedia
3. “Fruticose lichen IMG_0748” By Noj Han (CC BY-SA 2.0) via Flickr