Cladophora is a genus of branching filamentous green algae in the family Cladophoraceae (order Cladophorales, class Ulvophyceae, phylum Chlorophyta). First described by Friedrich Traugott Kützing in 1843, the genus has a worldwide distribution, occurring primarily in marine and brackish waters with some freshwater species. It may be referred to as reticulated algae, branching algae, or blanket weed.
The genus forms thalli of branched, uniseriate (one cell thick) filaments that are attached to substrates via rhizoid cells or a simple disc-like holdfast, though some grow unattached. Filaments are wider at the base and narrower at the tips, with cylindrical, barrel-shaped, or club-shaped cells. Cells are large and multinucleate, containing many parietal chloroplasts that typically join into a net-like reticular formation, each with a single pyrenoid. The bright grass-green color comes from chlorophyll a and b in ratios similar to higher plants, along with β-carotene and xanthophylls. Cell walls contain cellulose and pectin. Under unfavorable conditions, thick-walled akinetes may develop.
Cladophora can form dense mats in aquatic environments, which affect light penetration and oxygen levels. These mats also serve as habitat and food for various aquatic organisms. Temperature, water currents, and waves influence metabolism, morphology, and branching patterns.
The taxonomic history of Cladophora is complex: Kützing and subsequent authors described hundreds of species based on minor morphological differences, but extensive phenotypic plasticity means the same species can look drastically different in fresh versus salt water. In the 20th century, Christian van den Hoek synonymized many names. Molecular data has revealed cryptic diversity and demonstrated that Cladophora is polyphyletic — the simple branching morphology evolved independently multiple times. Taxonomists are now splitting Cladophora into smaller monophyletic genera, though the resulting genera often overlap morphologically. As of 2025, AlgaeBase accepts approximately 190 species within Cladophora.
Notable members include Cladophora glomerata (a widespread freshwater species), Cladophora rupestris (a common marine rock-dwelling species), and the former Cladophora aegagropila, now reclassified as Aegagropila linnaei (marimo, the popular aquarium "algae ball").
Distribution
Cladophora is a cosmopolitan genus with a worldwide distribution. It occurs primarily in marine and brackish waters, with some species found in freshwater. The genus is recorded from Africa, Asia, the Pacific Islands, Australia, Europe, the Atlantic Islands, North America, New Zealand, and the Caribbean. It inhabits diverse aquatic environments including lakes, ponds, dam reservoirs, large rivers, coastal littoral zones, and oceanic depths. In Europe, only about 15 species are freshwater. The genus thrives in hard water conditions with pH 7–10, high light intensity, and nutrient-rich environments.
Ecology
Cladophora is ecologically significant as both a beneficial and potentially problematic organism. Modest growth provides an important food source for fish and other aquatic animals, acts as a buffer for nutrient sequestration, and protects some aquatic organisms from solar ultraviolet radiation. However, under conditions of increased phosphorus loading (hypertrophication), Cladophora can undergo explosive growth, forming extensive floating mats. These mats prevent water circulation and aeration, block light from reaching photosynthesizing organisms below, and interfere with commercial fishing by clogging nets and lines. Rotting mats washed ashore reduce shoreline property values — a well-documented issue along the Great Lakes in the United States. The relationship between Cladophora blooms and invasive quagga mussel populations in the Great Lakes is an area of ongoing ecological study. Some Cladophora species are also investigated for phytoremediation, as they efficiently absorb heavy metals, pollutants, nitrogen, and phosphorus from contaminated water.
Cultivation
Cladophora is not cultivated in the traditional horticultural sense, but there is commercial demand for its biomass in value-added products including cosmetics and fertilizers. Algae balls (formerly Cladophora aegagropila, now Aegagropila linnaei, known as marimo) are significant in the hobby aquarium trade. In Laos, Cladophora is harvested from the Mekong River and consumed as a traditional food ("Mekong weed" or kaipen), eaten dried in sheets similar to nori, often with sesame, or used raw in soups and steamed curries.
Taxonomy
Cladophora was first described by Friedrich Traugott Kützing in 1843 and has had a long and complex taxonomic history. Kützing and subsequent authors described hundreds of species and varieties based on minor morphological differences. However, Cladophora displays extensive phenotypic plasticity — the same species may appear drastically different depending on environmental conditions such as salinity. In the 20th century, Christian van den Hoek and others synonymized many names, gradually reducing the number of accepted species. As of 2025, AlgaeBase accepts approximately 190 species.
Molecular phylogenetic studies have shown that the simple branching morphology of Cladophora evolved independently multiple times within Cladophorales, rendering the genus polyphyletic. Taxonomists have begun splitting Cladophora into smaller monophyletic genera including Pseudocladophora, Lychaete, Willeella, Lurbica, and Rama, though these genera often overlap significantly in morphology. A notable reclassification is Aegagropila linnaei (marimo), formerly Cladophora aegagropila.
Cultural Uses
Cladophora has several documented cultural and practical uses. In Laos, it is harvested from the Mekong River and consumed as a traditional delicacy known as "Mekong weed" or kaipen — dried into sheets similar to nori, often with sesame, and eaten as a snack, appetizer, or with meals. It is also eaten in Thailand and the Hawaiian Islands. The alga has pharmacological potential: it is reported to possess antimicrobial, antihistamine, antiviral, antioxidant, anti-inflammatory, and other bioactive properties with possible applications for diabetes, hypertension, and cancer, though it has not yet been commercialized as a pharmaceutical agent. Cladophora can also be converted into biodiesel through trans-esterification, though production depends on oil content. Its biomass is used in cosmetics and as fertilizer.
