Overview & Origin
Hygrophila polysperma is native to India and Malaysia, where it grows as a common weed in ditches, rice paddies, and waterways. It belongs to the family Acanthaceae and was introduced to the aquarium hobby decades ago as one of the hardiest available stem plants.
Its extreme hardiness is also its downfall in the wild — when released into non-native waters (particularly in the southern United States), it became highly invasive, outcompeting native vegetation. As a result, H. polysperma is classified as a Federal Noxious Weed in the U.S. and cannot legally be sold or transported across state lines. It remains legal in many other countries.
Care (Minimal)
Hygrophila polysperma requires almost nothing to thrive:
- Lighting: Any — grows in everything from dim ambient light to high-intensity LED. Under low light it stretches; under high light it stays compact and can develop pink/red upper leaves.
- CO2: Not needed at all. Grows aggressively without any supplementation.
- Substrate: Any — gravel, sand, aquasoil. Roots quickly from any node.
- Fertilizer: Benefits from but doesn't require fertilization. In fish-stocked tanks, waste provides sufficient nutrients.
Water Parameters
- Temperature: 68–86°F (20–30°C)
- pH: 5.5–8.0
- KH: 2–15 dKH
- GH: 2–20 dGH
Hygrophila polysperma has possibly the widest tolerance range of any aquarium plant.
Varieties
- Standard green: Light green leaves, very fast growing. The most common form.
- 'Rosanervig' (Sunset Hygro): White/pink veins on green leaves that become more pronounced under high light. More attractive but subject to the same legal restrictions.
Legal Status
In the United States, Hygrophila polysperma is listed as a Federal Noxious Weed under the Federal Plant Pest Act. It is illegal to sell, transport, or distribute across state lines. Some aquarists still keep it from local trades, but purchasing it from retailers who ship across state lines is prohibited.
In other countries, check local regulations. In many parts of Europe and Asia, it remains legal and widely available.
Common Problems & Solutions
- Growing too fast: The main "problem" — it can take over a tank quickly. Trim weekly and remove excess stems.
- Leggy growth: Under very low light, stems stretch with wide spacing between leaves. Increase light for more compact growth.
- Overtaking other plants: Its aggressive growth can shade out slower-growing plants. Keep it contained to one area and trim frequently.
Frequently Asked Questions
Is Hygrophila Polysperma legal?
In the U.S., it's a Federal Noxious Weed — illegal to sell or ship across state lines. Check regulations in your country before purchasing.
What's the easiest aquarium stem plant?
Hygrophila polysperma is widely considered the single easiest stem plant in the hobby. If it's not legal in your area, Hornwort and Water Wisteria are similarly easy alternatives.