Desmidiales

Tiny green plants live in fresh water.

These plants are called desmids. They are very small. You need a microscope to see them.

They have many pretty shapes. Some look like stars. Others look like round balls. Some even look long.

Many desmids have two matching halves. These halves are joined in the middle. They use sunlight to make food. This helps them grow.

Desmids like wet places like bogs. They like water that is a bit sour.

They are very sensitive. If the water changes, they may leave. This helps us know if water is healthy.

Desmids are tiny green algae. Most are just one cell. Some grow in long chains. They live in fresh water.

Desmids have many beautiful shapes. They can look like stars or long lines. Some are round. Because they are so symmetrical, people love to study them under microscopes.

Many desmids have two matching parts. These parts are called semicells. A narrow bridge joins them in the middle. This bridge is called an isthmus. Inside this bridge sits the nucleus. Each semicell has a chloroplast to make food from light. They also have pyrenoids. These help store power for later.

Desmids like sour water. This means the water has a low pH. They often live in bogs or marshes. They like places with little calcium. Desmids are very sensitive to change. If the water changes, they react. This makes them useful bioindicators. That means they help us check if a habitat is healthy.

Desmids are tiny green algae that live in fresh water. Most desmids are just one single cell. Some species grow in long chains called filaments. Others form small groups called colonies. These living things belong to a group called Charophyta. This is the same group where land plants first began. Scientists find desmids very interesting because of their shapes. They are highly symmetrical and look very attractive under a microscope.

How a desmid works depends on its clever structure. Most cells have two matching halves called semicells. A narrow bridge called an isthmus joins these halves together. The cell's nucleus sits right inside this bridge. Each semicell holds a large chloroplast to make food from light. They also have small parts called pyrenoids to store energy. Many desmids also have tiny pores in their cell walls. These pores let out a jelly-like substance called mucilage. This mucilage acts like a shield to protect the cell.

Learning about desmids involves looking at many different families. Scientists use different names to group them by their shapes. For example, the family Closteriaceae includes the genus Closterium. There are also families like Desmidiaceae and Peniaceae. Some scientists once thought the Mesotaeniaceae family belonged here too. However, DNA tests showed they are actually more closely related to the Zygnemataceae. Today, we recognize about 40 different genera of desmids. This helps experts keep track of all their different forms.

There are many amazing facts about these microscopic algae. There are between 5,000 and 6,000 different species in the world. Most desmids prefer acidic water with a pH between 4.8 and 7.0. They often live in places like bogs or marshes. They like water that does not have much calcium or magnesium. Some species are only found in certain parts of the world. For instance, Micrasterias ceratofera lives in the Indo-Malayan and North Australian regions. Allorgeia incredisibilis is found in equatorial Africa.

You can think of desmids as tiny helpers for nature. They are very sensitive to changes in their homes. Because they react to changes, scientists use them as bioindicators. This means they help us check if water is healthy. If the water quality changes, the desmids will change too. They live near plants like Utricularia or float freely in the water. Even though they are tiny, they play a big role in their tiny worlds.

Desmids are a diverse order of microscopic green algae known scientifically as Desmidiales. They belong to the class Zygnematophyceae within the division Charophyta. This division is significant because it is the group from which land plants, or Embryophyta, originally emerged. While most desmids are single-celled organisms, some species grow in long chains called filaments. Others form non-filamentous colonies where individual cells remain connected by threads or remnants of parent cell walls. Because of their highly symmetrical and attractive shapes, they are very popular subjects for both professional and amateur microscopists.

To understand how a desmid functions, one must look at its unique cellular morphology. Most desmids are divided into two symmetrical compartments known as semicells. These two halves are joined by a narrow bridge called an isthmus. The cell's spherical nucleus is located within this central isthmus. Each semicell contains a large, often folded chloroplast used for photosynthesis. They also contain one or more pyrenoids, which are structures used to form carbohydrates for energy storage. The cell wall consists of two distinct layers. The inner layer is composed mainly of cellulose. The outer layer is thicker and stronger, often featuring spines, granules, or warts.

Desmids also utilize specialized structures to interact with their environment. Many species possess mucilage-secreting pores within their cell walls. These pores release a translucent, gelatinous substance called mucilage that acts as a protecting agent. In some genera, like Micrasterias, these pores are spread uniformly across the wall. In other ornamented genera, such as Cosmarium, the pores are grouped symmetrically around spines or warts. The pore structure is complex. In the inner wall, the pore is a simple canal. In the outer wall, the canal is often surrounded by a cylindrical zone called a pore-organ. These canals are typically occupied by threads of mucilage being excreted from the cell.

Reproduction in desmids occurs through two primary methods. The most common method is asexual fission. During this process, the two halves of a cell separate from one another. Each half then develops into a completely new cell. Because the recently formed half is often smaller than the original, the resulting cell may appear asymmetric. Under adverse environmental conditions, desmids may undergo sexual reproduction through a process called conjugation. This process is shared with other closely related taxa in the Zygnematophyceae. However, sexual reproduction is considered rare, and many species have never been observed reproducing this way in the wild.

Taxonomically, the order Desmidiales is quite complex. It comprises approximately 40 genera and between 5,000 and 6,000 different species. Scientists often distinguish between "saccoderm" and "placoderm" desmids. Saccoderm desmids belong to the family Mesotaeniaceae and lack a central constriction or median suture lines. In contrast, placoderm desmids, which make up the order Desmidiales, feature two symmetrical halves and mucilage-secreting pores. Modern DNA analysis has changed how we classify these groups. For example, the family Mesotaeniaceae was once included in Desmidiales, but DNA evidence shows it is more closely related to the Zygnemataceae. Current classifications recognize three to five families within the order, including Closteriaceae, Gonatozygaceae, Peniaceae, and Desmidiaceae.

Desmids have very specific habitat requirements that dictate where they live. They are found in freshwater habitats globally but strongly prefer nutrient-poor wetlands like bogs and mires. They generally thrive in acidic waters with a pH between 4.8 and 7.0. They also prefer environments with low salinity and low amounts of dissolved calcium and magnesium. If nutrient levels in the water become too high, desmids are often quickly outcompeted by other organisms. They may live attached to aquatic vegetation, such as Utricularia, or they may be tychoplanktonic, meaning they float freely in the water column after being disturbed.

Because they are so sensitive to environmental changes, desmids serve a vital role as bioindicators. This means scientists study their presence and health to determine the quality of the water and the surrounding habitat. Their distribution is also influenced by their biology. Because desmids do not produce resting spores, they do not disperse as easily as other organisms. This leads to distinct regional floras. For example, the Indo-Malayan and North Australian realm features the species Micrasterias ceratofera. Meanwhile, equatorial Africa is characterized by species like Allorgeia incredibilis. Even in their tiny ecosystems, they are part of a complex web, facing parasites like chytrid fungi and being grazed upon by rotifers, ciliates, and crustaceans.