Japan hydrocotyle: the versatile trilobed creeper

A small-leaved pennywort

Hydrocotyle tripartita is a creeping marsh plant from Southeast Asia and Australasia, in the same genus as Brazilian pennywort but far smaller-leaved. The plant almost always sold as 'Japan' is a compact, small-leaved form prized for carpeting. Like its relatives it grows readily emersed and adapts well to submersed life.

Little three-lobed leaves

Each leaf is small and divided into three rounded lobes — the tripartita of the name — carried on a thin petiole from a wiry, branching creeping stem. The overall effect is a fresh, bright-green tangle. Grown flat it reads as a fine-textured carpet; allowed to pile up it forms a soft bushy mound, and it will happily climb over rock and wood.

Easy and adaptable

This is an easy, fast plant that tolerates a wide range of light and does not need CO₂. The main thing light controls is habit: under strong light it tends to stay low, dense and carpet-like, while in dimmer tanks it grows taller and more open, reaching for the surface. It is not fussy about feeding, drawing nutrients from both the water and its roots, and CO₂ simply makes it faster and tighter. Its speed is the main upkeep: expect regular trimming to keep a carpet flat.

Parameter	Value
Lighting	Low to high; stays lowest and tightest under strong light
CO2	Not required; grows faster and denser with it
Temperature	20–28°C
pH	6.0–7.5
Hardness	Soft to moderately hard
Fertiliser	Feeds from water column and roots
Substrate	Any; roots readily at the nodes
Growth rate	Fast
Placement	Foreground carpet to lower midground
Difficulty	Easy

Carpet, climber, or filler

Few plants are as flexible. Pinned to the substrate and trimmed, it makes a quick, forgiving foreground carpet — a good beginner alternative to the more demanding HC Cuba. Left to climb, it clothes hardscape in green; grown loose, it fills the midground. That versatility, plus its speed, makes it a favourite for softening a new layout fast.

It propagates itself

Propagation is effortless: the creeping stems root at their nodes as they spread, so lifting and replanting a portion, or simply letting it run, multiplies it quickly. Trimmings almost always take. To maintain a flat carpet, thin it periodically and replant the best runners — left completely alone it will mound up and eventually shade its own lower growth.

Growing up, not out

Tall, leggy growth instead of a flat carpet is the usual issue and most often reflects too little light, though crowding and lack of trimming contribute — brighten the light and trim it back to encourage a low habit. A carpet lifting off the substrate happens as the mat thickens and traps gas or shades its base; thin and replant it before it detaches. Early melt after planting is the normal emersed-to-submersed adjustment.

More plants in this series

• Brazilian pennywort — large-leaved cousin
• Monte Carlo — easy carpeting plant
• HC Cuba — the tiniest carpet
• Dwarf four-leaf clover — slow low carpet
• Glossostigma — classic bright carpet