Phaeophyceae: An In-Depth Exploration of Brown Algae

The diversity of life on Earth has always fascinated scientists, leading to various systems of classification over the centuries. Among the most influential was R.H. Whittaker’s Five Kingdoms System. This system categorized living organisms into five distinct kingdoms based on their cellular structure, mode of nutrition, physical form, reproductive capabilities, and phylogenetic relationships. The kingdoms—Protista, Plantae, Monera, Animalia, and Fungi—encompassed the vast array of life forms, each contributing uniquely to the biosphere.

Within the kingdom, Plantae lies a fascinating group of organisms known as algae. Algae are primarily aquatic, chlorophyll-containing organisms that range in complexity from simple unicellular forms to more complex multicellular structures. Their thalloid body plan, ability to perform photosynthesis, and autotrophic nature make them integral to aquatic ecosystems. They thrive not only in water but also in diverse environments such as moist stones, soil, and wood. Some algae form symbiotic relationships with lichens and animals, showcasing their adaptability and ecological significance.

The Diverse World of Algae

Algae are divided into several groups based on their pigmentation, storage products, and cell wall composition. The three main classes of algae are:

• Chlorophyceae (Green Algae)
• Rhodophyceae (Red Algae)
• Phaeophyceae (Brown Algae)

Each of these groups exhibits distinct characteristics and contributes uniquely to the ecosystem. Among these, the Phaeophyceae or Brown Algae are particularly interesting due to their unique pigmentation, ecological roles, and economic importance.

Phaeophyceae: The Brown Algae

The class Phaeophyceae comprises a diverse group of algae commonly known as brown algae. The name “brown algae” is derived from their characteristic color, which ranges from dark brown to olive green, owing to the presence of the pigment fucoxanthin. This pigment, in combination with chlorophylls a and c, gives brown algae their distinctive hue.

Brown algae are predominantly marine organisms, thriving in cold coastal waters across the globe. They can be found in a variety of habitats, from the rocky intertidal zones to the vast underwater forests known as kelp forests. These algae play a crucial role in marine ecosystems, providing food and habitat for a myriad of marine species.

Diversity and Morphology

With over 1,500 species, brown algae exhibit a remarkable diversity in size, shape, and structure. Some species, like Ectocarpus, are simple, filamentous algae, while others, such as the giant kelps (Macrocystis pyrifera), can grow to astounding lengths of up to 100 meters, forming dense underwater forests that are teeming with life.

The body of brown algae is typically multicellular and thalloid, meaning it lacks true roots, stems, and leaves. Instead, it consists of a holdfast, stipe, and blade, each serving specific functions:

• Holdfast: This root-like structure anchors the algae to the substrate, preventing it from being swept away by currents. The holdfast varies in complexity among different species, but unlike the roots of higher plants, it does not absorb nutrients or water. Instead, it solely serves as an attachment organ.
• Stipe: The stipe is a stalk-like structure that connects the holdfast to the blade. It can be either flexible or rigid, depending on the species. In some species, the stipe contains a hollow, septate core that helps the algae maintain buoyancy.
• Blade/Lamina: The blade, also known as the lamina or frond, is the flattened, leaf-like structure where photosynthesis primarily occurs. The surface of the blade can be smooth or wrinkled, depending on the species. In some brown algae, such as Sargassum, specialized gas-filled bladders called pneumatocysts are present near the blades. These structures help the algae float, ensuring that the photosynthetic tissues remain close to the water’s surface where light is abundant.

Cellular Structure and Pigmentation

The cell walls of brown algae are composed of two distinct layers: an inner layer of cellulose that provides structural support, and an outer layer made of a sticky substance called algin. Algin, a polysaccharide, gives brown algae their slimy texture and plays a significant role in their ability to withstand harsh environmental conditions, such as desiccation and mechanical stress from waves.

Brown algae contain a unique combination of pigments, including chlorophyll a, chlorophyll c, fucoxanthin, and various carotenoids. The dominant pigment, fucoxanthin (C42H58O6), is responsible for its characteristic brown color. This pigment absorbs light in the blue-green to yellow-green spectrum, which penetrates deeper into water than other wavelengths, allowing brown algae to photosynthesize efficiently even in deeper waters.

In addition to pigments, brown algae store energy in the form of complex carbohydrates. The primary storage compounds are laminarin and mannitol:

• Laminarin: A glucose polysaccharide, laminarin is a storage carbohydrate that provides energy to the algae. It is a linear polymer of glucose with occasional branching, typically linked by β(1→3) bonds.
• Mannitol: A sugar alcohol, mannitol serves multiple functions in brown algae. It acts as an osmoprotectant, helping the algae maintain cellular function in varying salinities, and as an antioxidant, protecting the cells from oxidative damage. Mannitol is also an important carbon storage compound, which the algae can metabolize when needed.

Reproductive Strategies of Brown Algae

Brown algae exhibit a wide range of reproductive strategies, including both sexual and asexual reproduction. This diversity in reproduction contributes to their adaptability and success in various marine environments.

Asexual Reproduction

Asexual reproduction in brown algae primarily occurs through the production of zoospores. These motile spores are typically pear-shaped and possess two flagella of unequal length, which allow them to swim through the water. Once the zoospores settle on a suitable substrate, they germinate and develop into new algal individuals.

In addition to zoospores, brown algae can also reproduce asexually through fragmentation. In this process, a piece of the algal thallus breaks off and develops into a new individual. Fragmentation is particularly common in species like Sargassum, where broken pieces can float away and establish new populations.

Sexual Reproduction

Sexual reproduction in brown algae is equally varied, with species exhibiting isogamous, anisogamous, or oogamous forms of reproduction:

• Isogamous Reproduction: In isogamous reproduction, the gametes are morphologically similar and motile. Both gametes have flagella and can move independently. An example of isogamous reproduction can be found in the genus Ulothrix.
• Anisogamous Reproduction: In anisogamous reproduction, the gametes are of different sizes, with the smaller, typically more motile male gamete and the larger female gamete. Both gametes are flagellated but differ in their morphology. The genus Ectocarpus exhibits anisogamous reproduction.
• Oogamous Reproduction: Oogamous reproduction involves the fusion of a large, non-motile female gamete (egg) with a smaller, motile male gamete (sperm). This form of reproduction is common in higher plants and is also observed in some brown algae, such as Fucus. The sperm cells swim towards the egg, guided by chemical signals, where fertilization occurs either within the oogonium or in the surrounding water.

Lifecycle of Brown Algae

The lifecycle of brown algae typically involves an alternation of generations, where a diploid sporophyte generation alternates with a haploid gametophyte generation. This lifecycle can be homomorphic, where the sporophyte and gametophyte generations are morphologically similar, or heteromorphic, where they differ in appearance.

For example, in Laminaria, the sporophyte is a large, conspicuous structure that produces haploid spores through meiosis. These spores develop into microscopic gametophytes, which produce gametes. Fertilization occurs, leading to the formation of a diploid zygote that grows into a new sporophyte.

Ecological and Economic Importance of Brown Algae

Brown algae play a vital role in marine ecosystems and have significant economic value due to their various applications in industry, medicine, and agriculture.

Ecological Importance

As primary producers, brown algae form the base of the food chain in many marine ecosystems. They capture energy from sunlight through photosynthesis and convert it into organic matter, which serves as food for a wide range of marine organisms, from small invertebrates to large herbivorous fish.

Kelp forests, formed by species like Macrocystis and Laminaria, are among the most productive and diverse ecosystems on Earth. These underwater forests provide habitat, food, and shelter for a vast array of marine life, including fish, invertebrates, and marine mammals. The dense canopy created by the kelp blades offers protection from predators and harsh environmental conditions, while the holdfasts create a complex, three-dimensional structure on the ocean floor that supports a rich community of organisms.

In addition to their role in supporting marine biodiversity, brown algae also contribute to global

carbon cycling. Through photosynthesis, they absorb significant amounts of carbon dioxide from the atmosphere and oceans, helping to mitigate the effects of climate change. When brown algae die, a portion of their biomass sinks to the ocean floor, sequestering carbon in the deep sea for long periods.

Economic and Commercial Uses

Brown algae have been harvested and utilized by humans for centuries, with applications ranging from food and medicine to industrial products. Some of the most notable uses include:

• Food Industry: Brown algae such as Laminaria and Sargassum are consumed as food in many cultures, particularly in East Asia. They are rich in essential nutrients, including iodine, potassium, and vitamins. In addition to being eaten directly, brown algae are also used as a source of alginic acid, a polysaccharide that serves as a thickening and stabilizing agent in a wide range of food products, including ice cream, salad dressings, and bakery goods.
• Medicine: Brown algae have been used in traditional medicine for their health benefits, particularly their high iodine content. Laminaria, for example, has been used to treat iodine deficiency disorders such as goitre. In modern medicine, derivatives of brown algae are used in various pharmaceutical applications. Sodium laminarin sulphate, extracted from Laminaria, is an anticoagulant used to prevent blood clotting. Additionally, brown algae have shown antibacterial and vermifuge properties, making them useful in treating infections and parasitic infestations.
• Industrial Applications: Brown algae are an important source of alginic acid, which is used in a variety of industrial applications. In the food industry, alginic acid is used as a thickener, stabilizer, and emulsifier. It is also used in the production of textiles, paper, and pharmaceuticals. In the battery industry, alginic acid is used as a binder in the production of electrode materials. Brown algae also contribute to the production of soda ash, which is used in the manufacture of glass and soap.
• Agriculture: Brown algae are used as natural fertilizers in agriculture, providing essential nutrients to crops and improving soil structure. They are particularly valued for their high content of trace elements and growth-promoting hormones. Seaweed extracts derived from brown algae are commonly used as biostimulants to enhance plant growth and resistance to stress.
• Environmental Applications: The ability of brown algae to absorb heavy metals from water has led to their use in bioremediation efforts. Algae such as Sargassum can accumulate metals like lead, cadmium, and mercury, making them valuable in the cleanup of polluted water bodies. Researchers are also exploring the potential of brown algae as a source of biofuels, given their high carbohydrate content and rapid growth rates.

Conclusion

The Phaeophyceae, or brown algae, are a remarkable group of marine organisms that play a crucial role in the health and productivity of marine ecosystems. Their unique morphology, diverse reproductive strategies, and ability to thrive in challenging environments have made them successful across a wide range of habitats. Beyond their ecological importance, brown algae have significant economic value, with applications in food, medicine, industry, and environmental management.

As we continue to explore the oceans and understand more about the biodiversity of marine life, the study of brown algae offers valuable insights into the complexities of life in the sea and the potential benefits these organisms can provide to humanity. Whether as a key component of marine ecosystems, a source of nutrition, or a contributor to various industries, brown algae are an essential part of our natural world, deserving of continued study and conservation efforts.

Informative Table for Key Overview of Phaeophyceae

The following table provides a comprehensive summary of the key aspects of Phaeophyceae, commonly known as brown algae. This table highlights their taxonomy, morphology, reproduction, ecological roles, and economic importance, encapsulating the detailed information provided in the previous sections. It serves as a quick reference guide for understanding the significance of brown algae in both natural ecosystems and various human industries.

This table condenses the extensive information on brown algae into a clear and organized format, making it easier to grasp the essential characteristics and significance of this group of marine organisms.

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Frequently Asked Questions (FAQs) about Phaeophyceae

What are Phaeophyceae, and why are they called brown algae?

Phaeophyceae is a class of algae commonly referred to as brown algae due to the presence of the pigment fucoxanthin, which gives them their characteristic brown to olive-green color. This pigment, along with chlorophylls a and c and other carotenoids, allows brown algae to absorb light efficiently, particularly in the blue-green spectrum, enabling them to thrive in deeper and colder marine environments. The name “Phaeophyceae” is derived from the Greek words “phaeo” meaning “dusky” and “phyceae” meaning “algae.”

Where are brown algae typically found?

Brown algae are predominantly marine organisms, thriving in cold coastal waters across the globe. They are commonly found in rocky intertidal zones, submerged nearshore environments, and kelp forests, which are some of the most productive and diverse marine ecosystems. These algae are particularly abundant in the Northern Hemisphere and along the coasts of continents like North America, Europe, and Asia. Some species, like Sargassum, are free-floating and can be found in vast mats, such as those in the Sargasso Sea.

What is the significance of fucoxanthin in brown algae?

Fucoxanthin is the primary xanthophyll pigment responsible for the brown or olive-green coloration of Phaeophyceae. This pigment plays a crucial role in photosynthesis by allowing brown algae to absorb light in the blue-green to yellow-green spectrum, which penetrates deeper into the water than other wavelengths. This ability enables brown algae to photosynthesize efficiently even in lower light conditions, such as in deeper waters or during low tides when light availability is reduced. Fucoxanthin also contributes to the algae’s adaptation to cold and nutrient-rich environments.

How do brown algae reproduce?

Brown algae exhibit both asexual and sexual modes of reproduction, contributing to their adaptability and widespread distribution. Asexual reproduction typically involves the production of zoospores, which are motile spores with two unequal flagella. These zoospores can swim through the water and settle on a suitable substrate to germinate into new individuals.

Sexual reproduction in brown algae can be isogamous, anisogamous, or oogamous:

• Isogamous reproduction involves the fusion of morphologically similar gametes, both of which are motile.
• Anisogamous reproduction features gametes of different sizes; typically, the smaller male gamete is motile, while the larger female gamete is less motile or non-motile.
• Oogamous reproduction involves the fusion of a large, non-motile egg with a smaller, motile sperm, similar to the reproductive strategies seen in higher plants.

The life cycle of brown algae often includes an alternation of generations, where a diploid sporophyte generation alternates with a haploid gametophyte generation. For example, in Laminaria, the sporophyte is the large, conspicuous form, while the gametophytes are microscopic.

What is the ecological role of brown algae in marine ecosystems?

Brown algae are vital primary producers in marine ecosystems, meaning they convert sunlight into organic matter through photosynthesis, forming the base of the marine food web. They provide essential nutrients and energy for a wide range of marine organisms, from small invertebrates to large herbivorous fish.

Kelp forests, formed by species like Macrocystis pyrifera (giant kelp), are some of the most productive ecosystems on Earth. These underwater forests create complex habitats that support a diverse array of marine life, including fish, invertebrates, and marine mammals. The dense canopy of kelp provides shelter and food, while the holdfasts create a three-dimensional structure on the ocean floor, fostering biodiversity.

Brown algae also contribute to carbon sequestration, helping to mitigate climate change. Through photosynthesis, they absorb significant amounts of carbon dioxide from the atmosphere and oceans. When brown algae die, a portion of their biomass sinks to the ocean floor, where it can be stored for long periods, thus playing a role in the global carbon cycle.

How do brown algae differ from green and red algae?

Brown algae (Phaeophyceae), green algae (Chlorophyceae), and red algae (Rhodophyceae) differ in several key aspects, including pigmentation, storage products, and habitat:

• Pigmentation: Brown algae contain fucoxanthin in addition to chlorophylls a and c, giving them their brown or olive-green color. Green algae primarily contain chlorophyll a and b, resulting in a bright green color, while red algae possess phycoerythrin and phycocyanin, which give them their red or reddish-purple color.
• Storage Products: Brown algae store energy in the form of laminarin and mannitol, whereas green algae store starch and red algae store floridean starch.
• Habitat: Brown algae are mostly found in marine environments, particularly in colder waters. Green algae are more diverse, with species found in both freshwater and marine habitats, as well as in moist terrestrial environments. Red algae are predominantly marine, especially in tropical and subtropical regions.

What is a holdfast, and what function does it serve in brown algae?

A holdfast is a root-like structure found in brown algae that anchors the organism to the substrate, such as rocks or other surfaces, preventing it from being carried away by water currents. Unlike the roots of higher plants, the holdfast does not absorb nutrients or water; its primary function is attachment. The structure of the holdfast can vary among different species, with some being simple and others more complex, depending on the environment in which the algae live. The holdfast is crucial for the survival of brown algae, especially in the turbulent intertidal zones where strong waves can easily dislodge unattached organisms.

What are pneumatocysts, and why are they important in brown algae?

Pneumatocysts are specialized gas-filled bladders found in some species of brown algae, such as Sargassum and Macrocystis. These bladders are primarily located near the lamina (blade) and serve to provide buoyancy to the algae, allowing the photosynthetic portions of the thallus to remain close to the water’s surface where light is more abundant. By keeping the blades afloat, pneumatocysts enhance the algae’s ability to capture sunlight, which is essential for photosynthesis. In large kelps, such as Macrocystis pyrifera, the pneumatocysts play a critical role in maintaining the vertical structure of the kelp forest, supporting the entire ecosystem that depends on these underwater forests.

How do brown algae contribute to the food industry?

Brown algae are extensively used in the food industry, particularly in East Asian cuisines where species like Laminaria and Sargassum are consumed as food. These algae are rich in essential nutrients, including iodine, potassium, and vitamins.

One of the most important compounds extracted from brown algae is alginic acid, a polysaccharide that serves as a thickening, gelling, and stabilizing agent in a wide variety of food products. Alginates derived from alginic acid are used in the production of ice cream, salad dressings, and bakery goods, where they help improve texture and stability. Additionally, brown algae are used in the production of agar and carrageenan, which are also utilized as gelling agents in various food products.

What are the medicinal uses of brown algae?

Brown algae have been used in traditional medicine for centuries, particularly for their high iodine content, which is essential for thyroid health. Laminaria, for example, has been used to treat iodine deficiency disorders such as goitre.

In modern medicine, derivatives of brown algae are used in various pharmaceutical applications. For instance, sodium laminarin sulphate, extracted from Laminaria, is an anticoagulant used to prevent blood clotting. Brown algae also possess antibacterial and vermifuge properties, making them useful in treating infections and parasitic infestations. Additionally, the high content of fucoidan in brown algae has attracted attention for its potential anti-cancer, anti-inflammatory, and immune-boosting properties, making it a subject of ongoing research in medical science.

What are kelp forests, and why are they important?

Kelp forests are underwater ecosystems formed by dense aggregations of large brown algae species, primarily those from the genera Macrocystis and Laminaria. These forests are some of the most productive and biodiverse ecosystems

on Earth, rivaling terrestrial rainforests in their ecological importance.

Kelp forests provide habitat and food for a wide variety of marine species, including fish, invertebrates, and marine mammals. The structure of the kelp creates a complex environment with different layers, much like a forest, allowing for high species diversity and abundance. Kelp forests also play a crucial role in coastal protection by buffering shorelines from the impact of waves and reducing coastal erosion.

Furthermore, kelp forests contribute to global carbon cycling by absorbing large amounts of carbon dioxide through photosynthesis. The biomass of kelp, when it dies and sinks to the ocean floor, can sequester carbon for long periods, making these forests important in the context of climate change mitigation.

How do brown algae adapt to their environments?

Brown algae have evolved several adaptations that enable them to thrive in various marine environments:

• Photosynthetic Pigments: The presence of fucoxanthin allows brown algae to absorb light in the blue-green spectrum, which penetrates deeper into the water, enabling them to photosynthesize efficiently in lower light conditions.
• Holdfasts: These structures anchor the algae to the substrate, allowing them to withstand strong currents and waves, especially in intertidal zones.
• Pneumatocysts: These gas-filled bladders provide buoyancy, keeping the algae’s blades near the water surface where sunlight is more abundant.
• Mucilage: Many brown algae produce a slimy substance called mucilage, which helps protect them from desiccation during low tides and reduces damage from UV radiation.

These adaptations have allowed brown algae to colonize a wide range of marine habitats, from shallow intertidal zones to deep subtidal regions.

What is the economic significance of alginates derived from brown algae?

Alginates are polysaccharides extracted from the cell walls of brown algae, particularly from species like Ascophyllum, Laminaria, and Macrocystis. These compounds are highly valued in various industries for their gelling, thickening, and stabilizing properties.

In the food industry, alginates are used in products such as ice cream, yogurt, and salad dressings to improve texture and consistency. They are also used in the production of edible films and coatings for food preservation.

In the pharmaceutical industry, alginates are used in wound dressings due to their ability to form a gel when in contact with moisture, providing a moist environment that promotes healing. They are also used as excipients in drug formulations to control the release of active ingredients.

In addition, alginates have applications in the cosmetic and textile industries, where they are used in the formulation of creams, lotions, and as thickeners in textile printing.

How do brown algae contribute to the cosmetics industry?

Brown algae are increasingly used in the cosmetics industry due to their rich content of bioactive compounds such as alginates, fucoidan, and polyphenols. These compounds are known for their hydrating, anti-aging, and antioxidant properties.

Alginates, extracted from brown algae, are used as thickening agents in creams, lotions, and facial masks. They help improve the texture and stability of cosmetic products. Fucoidan, another compound found in brown algae, is used in anti-aging products for its ability to enhance skin elasticity, reduce wrinkles, and promote skin regeneration.

Moreover, brown algae are used in formulations aimed at protecting the skin from environmental stressors such as UV radiation and pollution. Their antioxidant properties help neutralize free radicals, reducing skin damage and preventing premature aging.

What is the role of brown algae in bioremediation?

Bioremediation refers to the use of living organisms to remove or neutralize contaminants from the environment. Brown algae have shown great potential in this field due to their ability to absorb heavy metals and other pollutants from water.

Species like Ascophyllum nodosum and Laminaria digitata are known for their capacity to accumulate metals such as cadmium, lead, and mercury from polluted waters. This ability makes brown algae valuable in the treatment of industrial effluents and in the restoration of contaminated marine environments.

In addition to metal absorption, brown algae can also be used to remove excess nutrients, such as nitrogen and phosphorus, from water bodies. This process helps prevent eutrophication, a condition that can lead to the overgrowth of algae and subsequent depletion of oxygen in the water, which is harmful to aquatic life.

How do brown algae impact global carbon cycles?

Brown algae play a significant role in the global carbon cycle through the process of photosynthesis. By converting carbon dioxide (CO2) into organic matter, they help regulate atmospheric CO2 levels and contribute to carbon sequestration.

Kelp forests, in particular, are highly productive and can absorb large amounts of CO2. When brown algae die, a portion of their biomass sinks to the ocean floor, where it can be stored for long periods, effectively removing carbon from the short-term carbon cycle. This process of carbon sequestration is important in the context of climate change mitigation.

Additionally, brown algae release dissolved organic carbon (DOC) into the water, which can be utilized by marine microbes, further contributing to the marine carbon cycle.

What are the different types of thalli found in brown algae?

The thallus is the undifferentiated body of algae, and in brown algae, it can take on various forms depending on the species:

• Filamentous Thallus: Composed of thread-like filaments, as seen in species like Ectocarpus.
• Frondose Thallus: Leaf-like and flat, common in kelp species such as Laminaria.
• Encrusting Thallus: Grows as a crust over rocks, typical of species like Ralfsia.
• Siphonous Thallus: A single, large, multinucleate cell, characteristic of species like Codium.
• Pseudoparenchymatous Thallus: Resembling true tissue with complex cell organization, as seen in large kelps like Macrocystis.

These different thallus forms reflect the diversity of brown algae and their adaptation to various marine environments.

What are the industrial applications of brown algae beyond food and cosmetics?

Beyond food and cosmetics, brown algae have several other industrial applications:

• Biofuel Production: Brown algae are being explored as a potential source of biofuels due to their high carbohydrate content, which can be converted into ethanol or biodiesel.
• Agriculture: Extracts from brown algae, such as ascophyllum nodosum, are used as biofertilizers and soil conditioners to enhance crop growth and resistance to stress.
• Textile Industry: Alginates from brown algae are used as thickeners in textile printing and as stabilizers in fabric production.
• Pharmaceuticals: Brown algae are used in the production of various drugs and supplements, including those aimed at improving thyroid health and boosting the immune system.

These applications highlight the economic importance of brown algae across multiple sectors.

How do brown algae influence marine biodiversity?

Brown algae, particularly large kelps, play a crucial role in supporting marine biodiversity. By forming extensive underwater forests, they create habitats that support a wide variety of marine organisms, from small invertebrates to large predators.

Kelp forests provide shelter and food for species such as sea urchins, abalone, and fish, many of which rely on these environments for breeding and feeding. The complex structure of kelp forests also offers protection from predators and strong currents, contributing to the survival of many species.

Furthermore, the presence of brown algae in coastal ecosystems can influence the distribution and abundance of other species, shaping the overall community structure and contributing to the resilience of marine ecosystems.

What is the significance of brown algae in traditional medicine?

Brown algae have been used in traditional medicine for centuries, particularly in East Asia, where they are valued for their health-promoting properties. Species like Laminaria and Fucus are rich in iodine, which is essential for thyroid function and the prevention of disorders such as goitre.

In addition to their iodine content, brown algae contain compounds like fucoidan and laminarin, which have been studied for their potential anti-cancer, anti-inflammatory, and immune-boosting effects. These properties make brown algae a valuable resource in traditional remedies and modern herbal medicine.

Brown algae are also used in the preparation of health supplements and tonics aimed at improving overall well-being and treating specific health conditions, such as obesity, hypertension, and digestive disorders.