Asplenium polyodon (Bon Dhekia):

A Comprehensive Botanical and Ecological Study

Asplenium polyodon, locally known as Bon Dhekia in parts of eastern India and Bangladesh, is a graceful evergreen fern belonging to the family Aspleniaceae. Distinguished by its elongated fronds, glossy leaf surface, and preference for shaded, moisture-rich habitats, this species is a characteristic component of tropical forest understories and riparian ecosystems. Unlike marsh-dwelling dhekia ferns, Asplenium polyodon is primarily a forest-associated species, reflecting a distinct ecological strategy.

Bon Dhekia plays a subtle yet essential role in forest microclimates, soil stability, and moisture retention. Its presence often indicates undisturbed or moderately intact habitats with consistent humidity. This article presents a detailed, research-based examination of Asplenium polyodon, focusing on its taxonomy, morphology, habitat preferences, distribution, ecological role, and conservation considerations, with particular reference to its occurrence in the Sundarbans region.

Taxonomy & Classification

Asplenium polyodon belongs to one of the largest fern genera, Asplenium, which comprises species adapted to a wide range of ecological niches, from forest floors to rock crevices and epiphytic habitats.

• Kingdom: Plantae
• Division: Polypodiophyta (Pteridophyta)
• Class: Polypodiopsida
• Order: Polypodiales
• Family: Aspleniaceae
• Genus: Asplenium
• Species: Asplenium polyodon

Members of the Aspleniaceae family are characterized by linear or oblong sori arranged along veins, a feature that is clearly expressed in Asplenium polyodon.

Morphology & Field Identification

Growth Habit and Rhizome

Asplenium polyodon is a medium-sized, evergreen fern with a tufted growth habit. It arises from a short, erect or slightly creeping rhizome that is densely covered with brown to dark chestnut-colored scales. These scales protect the rhizome from desiccation and mechanical damage.

Frond Structure

The fronds are simple to shallowly lobed, lanceolate to narrowly elliptic in shape, and can reach lengths of 40–90 cm. The stipe is relatively short compared to the lamina and is dark green to brownish near the base.

The lamina is glossy, leathery, and deep green, with a pronounced midrib and numerous oblique lateral veins. Margins are finely toothed, a characteristic reflected in the species epithet polyodon, meaning “many-toothed.”

Reproductive Features

Sori are elongated and linear, arranged obliquely along the veins on the underside of the fronds. Each sorus is protected by a narrow, membranous indusium that opens toward the midrib. Spore production occurs primarily during humid seasons, ensuring optimal conditions for germination.

Habitat & Distribution

Global Range

Asplenium polyodon is distributed widely across tropical and subtropical Asia. Its range includes India, Bangladesh, Nepal, Bhutan, Myanmar, Thailand, Laos, Vietnam, southern China, Malaysia, Indonesia, and parts of the western Pacific.

The species is especially abundant in regions with monsoon-driven climates, where high humidity and shaded environments prevail for much of the year.

Preferred Habitat

This fern prefers shaded forest floors, rocky slopes, stream banks, moist ravines, and occasionally tree bases. It thrives in humus-rich soils with good drainage yet consistent moisture availability.

Asplenium polyodon is intolerant of prolonged waterlogging and high salinity, which distinguishes it ecologically from wetland dhekia ferns.

Occurrence

The occurrence of Asplenium polyodon is closely tied to seasonal moisture regimes. Frond growth is most vigorous during the monsoon and post-monsoon periods, while growth slows during extended dry spells.

As an evergreen species, it retains functional fronds throughout the year in favorable microclimates, contributing to stable ground cover in forested habitats.

Preferred Habitat in the Sundarbans Region

Within the Sundarbans, Asplenium polyodon is confined to non-saline, shaded microhabitats. These include elevated embankments, freshwater forest patches, village groves, and areas along freshwater canals where salinity influence is minimal.

The fern is absent from core mangrove zones but may occur in transitional landscapes where terrestrial forest elements intersect with deltaic systems.

Ecological Role

Asplenium polyodon contributes significantly to forest-floor ecology. Its dense frond canopy helps regulate soil temperature and moisture, reducing evaporation and creating favorable conditions for microorganisms and invertebrates.

The fern also plays a role in soil formation by trapping organic debris and leaf litter, which decomposes to enrich the forest substrate.

Habitat Alteration

Anthropogenic Pressure

Deforestation, land conversion, and infrastructure development reduce shaded forest habitats essential for Asplenium polyodon. Removal of canopy cover leads to increased light exposure and soil drying, which negatively affects fern populations.

Environmental Stress

Altered rainfall patterns and prolonged dry periods associated with climate variability further threaten suitable microhabitats, particularly in fragmented landscapes.

Conservation Efforts

Although Asplenium polyodon is not globally threatened, localized conservation measures are important. Protecting forest understory vegetation, maintaining riparian buffers, and preserving freshwater forest patches contribute to population stability.

Community-based forest stewardship and awareness of fern diversity can further support conservation outcomes in ecologically sensitive regions.

Did You Know?

• The genus Asplenium includes over 700 species worldwide.
• Bon Dhekia prefers stable humidity and avoids open, sun-exposed habitats.
• Its glossy fronds help reduce water loss in shaded forest environments.
• The species often grows alongside mosses and liverworts.

External Reference

For additional botanical and taxonomic information, consult: https://en.wikipedia.org/wiki/Asplenium