Hydrocotyle verticillata aka Whorled Marsh Pennywort

Hydrocotyle verticillata is a wetland obligate species that requires constantly moist to wet conditions. When grown as a houseplant or in a terrarium, keep the soil consistently wet or place the pot in a tray of water. The plant is very sensitive to dry soil and will quickly decline if allowed to dry out. For aquarium use, it can be grown fully submerged or emersed with roots in water.

Hydrocotyle verticillata thrives in temperatures between 68-82°F (20-28°C) but can survive a wider range of 41-86°F (5-30°C). It's hardy in USDA zones 7-11. In cooler climates, it can be grown as a seasonal outdoor plant or kept indoors year-round. Avoid prolonged exposure to freezing temperatures.

As a wetland plant, Hydrocotyle verticillata prefers high humidity environments. When grown emersed (above water), it benefits from humidity levels above 60%. Terrariums and paludariums provide ideal conditions. If growing in a regular pot, misting regularly or using a humidity tray helps maintain healthy growth.

Hydrocotyle verticillata propagates easily through runners and stem cuttings. Cut lateral shoots that include at least one leaf and some stem, then replant in moist substrate or float in water until roots develop. The plant produces new plantlets at nodes along the stems. Division of established clumps by separating rooted sections is also effective.

Hydrocotyle verticillata is native to North and South America and the West Indies. In the United States, it's broadly distributed across southern states from California to New Jersey, reaching its northern limits in New York and southern New England. It grows naturally in marshes, bog margins, pond edges, and other wetland habitats on coastal plains and islands.

Hydrocotyle verticillata can grow outdoors in USDA zones 7-11. It thrives in pond margins, bog gardens, and wet areas with sandy or gravelly shores. The plant prefers fluctuating water levels similar to coastal plain ponds. In colder climates, grow it as an annual or overwinter indoors. It associates well with other wetland plants like sedges and rushes.

Regular trimming is essential to control spread and encourage bushy, compact growth. Simply cut stems at any point along their length using scissors. This encourages the plant to grow thicker rather than taller. Without pruning, it can quickly overtake other plants in an aquarium or container. Cuttings can be replanted to propagate new plants.

Hydrocotyle verticillata produces inconspicuous small white flowers arranged in whorled clusters on short stalks below the leaves. Flowering occurs from early summer to early fall (July-September), but only when grown emersed with leaves above water. Each inflorescence has 2-12 whorls of tiny radially symmetrical flowers with five petals. The plant is unlikely to flower when grown fully submerged.

Yellow leaves (chlorosis) in Hydrocotyle verticillata typically indicate iron deficiency. Add a chelated iron supplement to address this. Other causes include insufficient nutrients, inadequate lighting, or the natural melting process when transitioning from emersed to submerged growth. Ensure balanced fertilization with liquid fertilizers and adequate light levels.

Slow growth in Hydrocotyle verticillata is usually caused by one of three factors: insufficient light, lack of CO2, or poor nutrients. When grown submerged, growth is naturally slower than emersed growth and benefits significantly from CO2 injection. Increase lighting to medium-high levels, ensure regular liquid fertilizer dosing, and consider adding CO2 supplementation for faster growth.

Hydrocotyle verticillata is relatively pest and disease resistant. The main issue is algae growth on leaves in high-light aquarium setups, which can be controlled by maintaining balanced nutrients and introducing algae-eating shrimp or snails. Melting (leaf die-back) commonly occurs when transitioning from emersed to submerged growth but is temporary—new leaves will emerge once roots establish.

When grown outdoors, Hydrocotyle verticillata dies back in winter in cooler climates (below zone 7) but returns from roots in spring in warmer zones. Indoor plants maintain consistent growth year-round with stable temperatures and lighting. Growth rate may slow somewhat in winter with reduced natural light. Supplemental lighting can help maintain active growth during shorter days.