Hydrodictyon patenaeformae Pocock: A new report from India

Introduction

The genus Hydrodictyon (Linn.) Lagerheim, a member of division Chlorophyta, family Hydrodictyaceae, order Sphaeropleales, is composed of thousands of cylindrical cells joined by adjacent edges forming various mesh structures, like tri, tetra, penta, hexa, septa and octagonal, etc (Table-1). Resembling a fishing net-like structure, due to which Hydrodictyon is famously known as Water Net and is easily visible to naked eyes [1]. This alga is characteristic of warm temperate zone and is widely distributed all over the globe including North Africa, America, Asia, New Zealand and Europe [2].

The genus Hydrodictyon has a greater ecological impact on the living biota of agricultural fields or seasonal or temporary water bodies [3]. They are found abundantly in slowly moving water streams, drains, river banks, agricultural lands filled with water and lakes. Till date altogether globally total six species of the genus Hydrodictyon are taxonomically accepted and these are H. africanum, H. indicum, H. majus, H. patenaeformae, H.  reticulatum, H. tertiarum [4], out of which only one species H.  reticulatum is ubiquitous in occurrence and has been reported from different countries of the world and well characterized.

The colonies of the genus Hydrodictyon are three-dimensional and net-like where cells form an interconnected mesh or tube that is defined by the network of cells. The genus Hydrodictyon is coenocytic with vegetative and sexual cycles, also producing a polyeder [5]. Pickett-Heaps [6] demonstrated that the germ net of Hydrodictyon forms a flat reticulate coenobium with the outer cells possessing two lobes, thus revealing an alliance with Pediastrum [7]. Phylogenetic analyses of the 18S data resolved Hydrodictyon as a monophyletic group but with bootstrap support less than 70% [7].

The present communication deals with the diversity of the genus Hydrodictyon from two natural fresh-water biotopes including the Chetawala Ghat, Ganga Khadar, Hastinapur, Meerut, India and Cantonment area near the Kendriya Vidyalaya Sikh Lines, Meerut Cantonment, Meerut, India.

Materials and Methods

Study sites and sampling:

Total 159 mixotrophic algal growth containing samples were collected from two different biotopes including the bank of Chetawala Ghat, Ganga Khadar, Hastinapur and Cantonment area near the Kendriya Vidyalaya Sikh Lines, Meerut Cantt., Meerut, India from 2018-2026 (Fig. 2A-D). Each sample was assigned with sample number along with the date of collection. Five ml from each sample was preserved in 4% v/v formaldehyde and deposited at the Department of Botany, Chaudhary Charan Singh University, Meerut, Uttar Pradesh, India.

Morphological observations

Samples from nature, enriched unialgal cultures were subjected to microscopic observations with the help of a Research Microscope (Olympus, CH21i) fitted with digital Camera (Magnus, Magcam-DC10) and their morphometric parameters were recorded with the help of image analysis software (MagVision). All the isolated strains were identified up to species level with the help of available literatures and monographs [2, 10].

Results

Thallus of the genus Hydrodictyon is colonial, forming hollow, cylindrical to sac-like structures that resemble a mesh or net. These colonies are typically free-floating often accumulate in vast quantities frequently to blanket the surface and undergo sudden changes in buoyancy and causing them to disappear only to quickly reappear especially during calmer periods. Free-floating mats of Hydrodictyon can vary considerably in size, ranging from a few millimeters to several centimeters in length. The net is composed of regularly arranged polygonal meshes, most commonly pentagonal or hexagonal, which impart a highly organized geometric appearance. Each mesh is formed by elongated cells joined end-to-end at distinct angles, creating a continuous reticulate framework. The colony lacks differentiation into specialized tissues, but its structural organization reflects a high degree of coordination among constituent cells. The macroscopic visibility of the colony, cellular dimensions, quantity, morphology of chloroplasts, and the granule count within each filament were documented for morphological characterization and identification of Hydrodictyon.

Total three species of Hydrodictyon including H. reticulatum; H. indicum and H. patenaeforme, observed from the Meerut region of Uttar Pradesh, India. Of which H. reticulatum was observed from both the biotopes while H. indicum was observed only from the drains of Cantonment area near the Kendriya Vidyalaya Sikh Lines Meerut. The genus H. patenaeforme, new to the flora of India was observed only from Chetawala Ghat, Ganga Khadar, Hastinapur, Meerut, Uttar Pradesh, India.

Morphological description

Family: Hydrodictyaceae

Genus: Hydrodictyon Roth

Key to the species

1. Coenocytes cylindrical and not generally separating at maturity, cell wall 2 layered and uniform, coenocytes up to 250µm broad and up to 1.5cm long………………H. reticulatum
2. Coenocytes cylindrical and separating at maturity, cell wall thick and lamellated and with knob like projections into protoplasm, coenocytes up to 1000µm broad and 1.6cm long………………………….……………………………………………….… H. indicum
3. Net flattened, younger colonies may show rhombic or triangular meshes, single layered, of several hundred cells, coenocytes cylindrical 800µm -1.2cm….………… H. patenaeformae

Hydrodictyon reticulatum (Linn.) Lagerheim (Fig. 3A-D)

Thallus macroscopic and colonial, grass green and free floating with closed cylindrical sac-like net. Four to seven cells of colony adjoined to each other at the end walls repeatedly forming a tetragonal to septagonal net like structure. Net may vary in sizes from 400-1900cm. Cells elongated, deeply green, cylindrical and very big, about 100-130 µm long and 10-12 µm broad, cell wall very thick and lamellated with numerous short knob-like portions of the cell wall projecting into the thin layer of protoplasm inside with smooth, two layered cell-wall. Chloroplast reticulate, young cells have a band-shaped chloroplast; mature cells have a reticulate (net-like) chloroplast with many pyrenoids; each cell of the net can produce a net asexually.

Location: 29.154966N; 78.078275E

Habitat: Chetawala Ghat, Ganga Khadar, Hastinapur and the Cantonment area near the Kendriya Vidyalaya Sikh Lines Meerut, Uttar Pradesh, India

Hydrodictyon indicum Iyengar (Fig. 4A-D)

Thallus macroscopic, deeply green and non-motile colonial. The cells are cylindrical and free-floating. Six cells of the colony are adjoined to each other at the end walls repeatedly forming small hexagonal net like structure. Nets may vary in sizes from 300-720cm. Coenobium forming a hollow cylindrical network. Cells short, elongated, light green, cylindrical about 10-13 μm long and 5.6-7 μm broad united at their corners in groups of three. Cell wall very thick and lamellated projecting into the thin layer of protoplasm. Chloroplast reticulate, young cells contain a single, band-shaped parietal chloroplast with one pyrenoid while mature cells become coenocytic (multinucleate) with a reticulate (net-like) chloroplast with many pyrenoids.

Location: 29.154966N; 78.078275E

Habitat: Cantonment area near the Kendriya Vidyalaya Sikh Lines Meerut, Uttar Pradesh, India

H. patenaeforme Pocock (Fig. 5A-F)

Thallus macroscopic, floating, fragile forming net-like tufts or mats within the water column. Nets bright green and composed of regularly arranged meshes, most commonly pentagonal or hexagonal, with highly organized geometric appearance. Nets very large, reaching several centimeters, and sometimes up to 1 meter in length. Cells elongated, light green, cylindrical about 90-113 μm long and 20-24 μm broad, coenocytic cells are typically linked at their ends to two other cells. Cells mostly pentagonal or hexagonal; some species or younger colonies may show rhombic or triangular meshes. Younger colonies may show rhombic or triangular meshes, single-layered, of several hundred cells, Coenocytes cylindrical linked at their ends to two other cells Cell wall very thick and lamellated. Individual young cells are uninucleate with a single chloroplast, while older cells become coenocytic (multinucleate) with large net-like reticulate chloroplast with numerous pyrenoids.

Location: 29.154966N; 78.078275E

Habitat: Chetawala Ghat, Ganga Khadar, Hastinapur, Meerut, Uttar Pradesh, India.

Discussion

In India, the diversity of the genus Hydrodictyon appears limited when assessed solely on species richness, yet its ecological significance and spatial distribution across freshwater habitats are notably substantial. According to available taxonomic databases, the genus is represented globally by six confirmed species and three varieties [4], indicating a modest level of taxonomic diversification. However, within the Indian subcontinent, only two species have been formally documented to date [11-13]. This apparent disparity between global diversity and regional records may reflect under-exploration, taxonomic ambiguities, or limitations in molecular characterization studies in India.

Despite the limited number of species, Hydrodictyon demonstrates extensive geographical distribution across diverse aquatic ecosystems in India, including ponds, lakes, reservoirs, wetlands, and slow-flowing rivers. The genus typically thrives in stagnant or slow-moving, nutrient-rich freshwater bodies, particularly during warmer months and monsoon seasons, where it may form dense floating mats [14]. Reports from regions such as Chennai, Uttar Pradesh, West Bengal, Himachal Pradesh, Uttarakhand, and other parts of the Gangetic plains confirm its widespread occurrence [15-19]. Despite the low number of reported species, Hydrodictyon plays a crucial ecological role in freshwater ecosystems by contributing to primary productivity, nutrient cycling, and habitat structuring, thereby underscoring the need for more comprehensive taxonomic and ecological investigations in the region [20-22].

From a taxonomic perspective, the apparent low diversity of Hydrodictyon in India may be attributed to under-exploration, morphological plasticity, and the lack of integrative taxonomic approaches combining molecular and ultrastructural data [23]. Many floristic surveys report Hydrodictyon only at the genus level, suggesting possible cryptic diversity that remains unrecognized [24]. Furthermore, regional studies have often focused on broader algal diversity, leading to insufficient detailed documentation of this genus [25].

The Meerut region of India has been explored by many biologists [26-36] but no such reports on the diversity of Hydrodictyon from the Meerut region are available till date. From the present communication we are reporting three species of Hydrodictyon including H. reticulatum; H. indicum and H. patenaeforme from the Meerut region of Uttar Pradesh, India. Of the three species, H. patenaeforme reported from Chetawala Ghat, Ganga Khadar, Hastinapur, Meerut, Uttar Pradesh is the first report and new addition to the macroalgal flora of India.

Conclusion

From the present communication, it could be concluded that, the Meerut region including Hastinapur of Uttar Pradesh, is rich in bio-diversity of micro and macroalgae including Hydrodictyon. The colonies of Hydrodictyon are free-floating often accumulate to blanket the surface undergoing sudden changes in buoyancy and causing them to disappear during calmer periods. Of the three species of Hydrodictyon, H. patenaeforme reported for the first time from Chetawala Ghat, Ganga Khadar, Hastinapur, Meerut, Uttar Pradesh, India and is a new addition to the Hydrodictyon flora of India.

Acknowledgement

Authors are thankful to the Dr. Rama Kant, Head, Department of Botany, Chaudhary Charan Singh University, Meerut, India for providing necessary facilities. Authors (RK and KS) are thankful to the U.P. Govt., Lucknow for financial support. We are thankful to the U.P. Govt., Lucknow for financial support. Authors are thankful to Prof. G.L. Tiwari, Ex. Head, Botany Department, University of Allahabad, Prayagraj, India for identification of the algal species.

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