Java Fern 'Thor's Hammer'

Quick facts

Identity

Also known as

Microsorum pteropus Thor's Hammer

Synonyms

Leptochilus pteropus; Polypodium pteropus; Microsorum pteropus 'Windelov'

Environment

Freshwater

Native to

Malaysia, Thailand, Indonesia, Southeast Asia

Habitat

Streams, rivers and waterfalls in tropical Southeast Asia, growing attached to rocks, wood and roots both submerged and along humid banks above the waterline

Sourcing

Captive-bred

Conservation

Not Evaluated

Care

Care level

Easy

Growth form

Rhizome

Max height

3 – 12 in (7.6 – 30 cm)

Spread

12 in (30 cm)

Growth rate

Slow

Placement

Midground, Background, Epiphyte

Water

Temperature

68 – 82 °F (20 – 28 °C)

pH

6.0 – 7.5

GH

2 – 15 dGH

PAR

15 – 40 PAR

Flow

Low-Moderate

Light

Low

CO₂

Beneficial

Planting

Substrate

Not needed

Feeds from

Water column

Fertilizer needs

Low

Colors

Green

Feeding & breeding

Propagation

Rhizome division, Plantlets

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Care guide

Overview

Narrower blades taper into irregular, forked tips unlike the simple points of standard Java Fern, a trait unique to this Polish-bred line. It remains easy to keep, tolerating low light and a wide parameter range, with its rhizome fixed to hardscape rather than substrate.

Care

Java fern is among the most forgiving plants sold for freshwater aquariums, tolerating a wide swing in temperature, pH and hardness as long as it is never planted in substrate. The rhizome, the thick horizontal stem from which fronds and roots emerge, must sit on top of the substrate or be tied or glued to driftwood or rock; burying it invites rot and eventual death of the plant. It grows steadily under low to medium light without added CO2, though modest CO2 and moderate light will speed up frond production. Many herbivorous fish leave the tough, slightly bitter leaves alone, making it a good choice for tanks with grazing fish.

Planting & trimming

Attach the rhizome to driftwood, rock or other hardscape using cotton thread, fishing line or aquarium-safe glue, keeping the rhizome itself fully exposed above the substrate surface. Roots will grip the hardscape within a few weeks, after which ties can be removed. Older, larger leaves and any blackened fronds can be trimmed at the base to keep the plant tidy and redirect energy into new growth. It can also be left loosely weighted or floating, and adapts to being grown emersed in paludariums with high humidity.

Fertilizing

Java fern draws most of its nutrients through its leaves and roots directly from the water column rather than the substrate, so liquid fertilizer dosed regularly is more useful than root tabs. It responds well to a complete liquid fertilizer containing iron and trace elements, especially in low-tech setups where it is the main nutrient consumer. Pale new growth or transparent patches on older leaves usually point to an iron or potassium shortfall rather than a lighting problem. Because uptake is slow, overdosing fertilizer is rarely a concern with this species.

Propagation

New plants are most easily produced by dividing the rhizome with a clean cut, ensuring each section retains a few leaves and root growth. Mature leaves also develop small plantlets along their edges or tips, especially on older or damaged fronds, which can be separated once they have a few roots and small leaves of their own and tied to new hardscape. Both methods are simple and reliable, making the species easy to share or propagate at home.

Problems

Small black or brown dots on the underside of mature leaves are sori, the plant's spore-producing structures, and are a normal sign of health rather than disease. Sudden parameter swings or transplant stress can trigger blackening and disintegration of fronds, often called melt, though the rhizome usually survives and resprouts if kept clean. Because growth is slow, algae can settle on older leaves in high-light tanks; trimming affected fronds and improving flow around the plant usually resolves it. Rhizome rot from burial in substrate is the most common cause of decline reported by hobbyists.

Sources

1. Java Fern Windelov 'Hybrid' - Buce Plant
2. Windelov java fern care: light, CO2 and placement · TankBud
3. Windelov Java Fern (Microsorum Pteropus Windelov) Care Guide
4. Java Fern 'Windelov' (Microsorum pteropus 'Windelov') | Aquatic Plants – Superior Shrimp & Aquatics

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