Cyclosorus dentatus (Bish Dhekia):

A Comprehensive Botanical and Ecological Review

Cyclosorus dentatus, commonly known as Bish Dhekia in eastern India and parts of Bangladesh, is a moisture-loving fern species widely associated with tropical wetlands, floodplains, and lowland freshwater ecosystems. The species is notable for its robust growth, distinctive dentate pinnae margins, and strong ecological association with seasonally inundated landscapes. Although often grouped locally with other “dhekia” ferns, Cyclosorus dentatus is botanically distinct and ecologically significant.

This fern plays a critical role in maintaining wetland structure and ecological balance by stabilizing soil, retaining moisture, and supporting diverse microhabitats. The following article presents an in-depth, research-oriented examination of Cyclosorus dentatus, covering its taxonomy, morphology, habitat preferences, geographic distribution, ecological roles, and conservation concerns, with special emphasis on its occurrence in the Sundarbans region.

Taxonomy & Classification

Cyclosorus dentatus is a member of the fern family Thelypteridaceae, a taxonomic group well adapted to humid and semi-aquatic environments. Its classification reflects morphological traits such as dentate pinnae margins, round sori, and creeping rhizomes.

• Kingdom: Plantae
• Division: Polypodiophyta (Pteridophyta)
• Class: Polypodiopsida
• Order: Polypodiales
• Family: Thelypteridaceae
• Genus: Cyclosorus
• Species: Cyclosorus dentatus

Within the genus Cyclosorus, this species is distinguished by its sharply toothed pinnae margins and its strong preference for saturated soils, making it a reliable indicator of freshwater wetland conditions.

Morphology & Field Identification

Growth Habit and Rhizome Structure

Cyclosorus dentatus is a medium to large-sized terrestrial or semi-aquatic fern that forms dense colonies under favorable conditions. It arises from a creeping to short-erect rhizome that anchors deeply into moist, fine-textured soil, allowing the plant to withstand periodic flooding.

Frond Characteristics

Fronds typically range from 60 to 130 cm in length and are pinnate to bipinnate in structure. The rachis is firm yet flexible, supporting numerous elongated pinnae arranged alternately. The defining feature of the species is the distinctly dentate or serrated margins of the pinnae, which are clearly visible during close field inspection.

The upper surface of the fronds is medium to dark green, while the underside is slightly paler. Texture ranges from soft in young fronds to moderately leathery in mature specimens.

Reproductive Structures

Fertile fronds bear rounded sori positioned regularly along the veins on the abaxial surface of the pinnae. Each sorus is covered by a thin, reniform indusium. Spore release typically coincides with periods of high humidity, ensuring effective dispersal.

Habitat & Distribution

Global Range

Cyclosorus dentatus has a broad distribution across tropical and subtropical regions of Asia and the western Pacific. Its range includes eastern and southern India, Bangladesh, Sri Lanka, Nepal’s lowlands, Myanmar, Thailand, Malaysia, Indonesia, southern China, and parts of the Pacific Islands.

The species is particularly abundant in monsoon-influenced regions where consistent moisture supports year-round vegetative growth.

Preferred Habitat

This fern thrives in freshwater wetlands, swampy grasslands, canal banks, paddy field margins, and riverine floodplains. It prefers silty or loamy soils rich in organic matter and demonstrates high tolerance for waterlogged conditions.

While partial shade promotes optimal growth, Cyclosorus dentatus can tolerate open sunlight provided adequate soil moisture is maintained.

Occurrence

Seasonal occurrence of Cyclosorus dentatus is closely linked to rainfall and hydrological cycles. New fronds emerge rapidly at the onset of the monsoon, followed by peak biomass accumulation during the rainy and post-monsoon months.

During dry seasons, fronds may senesce or reduce in size, but underground rhizomes remain viable, enabling rapid regeneration with the return of favorable conditions.

Preferred Habitat in the Sundarbans Region

Within the Sundarbans delta, Cyclosorus dentatus is confined primarily to freshwater pockets such as rain-fed ponds, village wetlands, canal embankments, and transitional zones between agricultural land and mangrove forest.

Although salinity limits its distribution in core mangrove areas, freshwater inflows during the monsoon create temporary habitats where the species flourishes. In these microhabitats, Bish Dhekia contributes to vegetation diversity and soil stabilization.

Ecological Role

Cyclosorus dentatus plays a vital ecological role in wetland systems. Its extensive rhizome network binds loose soil, reducing erosion along pond edges, embankments, and floodplains.

The fern provides shelter for amphibians, insects, mollusks, and microorganisms, thereby enhancing biodiversity. Leaf litter from senescent fronds contributes organic matter, supporting nutrient cycling and improving soil fertility.

Habitat Alteration

Anthropogenic Impacts

Drainage of wetlands for agriculture, urban expansion, and aquaculture development poses significant threats to natural populations of Cyclosorus dentatus. Alteration of natural water flow disrupts the hydrological conditions essential for its survival.

Environmental Stressors

Climate variability, including erratic rainfall and prolonged droughts, further affects habitat suitability. In deltaic systems, increasing salinity intrusion presents an additional challenge, particularly in low-lying areas.

Conservation Efforts

While Cyclosorus dentatus is not currently considered globally threatened, localized conservation measures are essential. Protection of freshwater wetlands, maintenance of natural drainage patterns, and reduction of chemical runoff can support long-term population stability.

Community-based wetland management and awareness of fern biodiversity can further enhance conservation outcomes, particularly in ecologically sensitive regions like the Sundarbans.

Did You Know?

• Bish Dhekia is often avoided for consumption due to its bitter and potentially irritating properties.
• The species serves as a reliable indicator of freshwater wetland health.
• Its spores disperse most efficiently during humid monsoon conditions.
• Dense fern growth can help reduce surface water evaporation.

External Reference

For additional botanical and taxonomic details, consult:

https://en.wikipedia.org/wiki/Cyclosorus_dentatus