Ludwigia arcuata: the fine needle-leaf ludwigia that burns orange-red

A North American wetland native

Ludwigia arcuata is native to the wetlands of the southeastern United States, which makes it one of the more temperature-tolerant colour stems — it copes with cooler water than tropical reds and is sometimes used in unheated or coolwater setups. It grows emersed along pond and ditch margins and submersed in shallow water.

There is genuine taxonomic muddle worth knowing about: much of what is sold as Ludwigia arcuata is actually the closely-related Ludwigia brevipes or a hardy arcuata × repens hybrid. It matters, because the true species is generally reckoned the more demanding of the group, while the hybrid usually on shop shelves is noticeably more forgiving. The care below describes the forgiving plant most often sold under this name — if you have the true species, expect it to be finickier, especially without CO₂.

Needle leaves that turn to fire

The narrow, almost pine-like leaves are what set it apart: where most reds are broad and paddle-shaped, arcuata is delicate and wiry, giving a fine texture that contrasts nicely with larger-leaved plants. Under strong light and modest nitrogen the needles flush orange to coppery red, brightest at the tips.

As with every colour stem on this site, we will be straight about the mechanism: light is the main driver of the red, and the ‘lean nitrogen deepens colour’ effect is a consistent hobby observation with a plausible physiological basis rather than a precisely proven rule. In low light it simply stays green and grows more loosely.

How to keep it

The hybrid usually sold as arcuata is forgiving for a colour plant. It does not demand CO₂, though it is denser and more richly coloured with it, and it will grow in inert substrate provided the water column is fed. The true species is fussier and is often reported as hard to keep long-term submersed without CO₂. Either way, the recipe for the best colour is strong light plus a full micronutrient mix with iron, and nitrate kept present but modest. Use the fertiliser comparison calculator to see which all-in-ones carry enough iron and micros to support colour.

Parameter	Value
Lighting	High for red; stays green under low light
CO2	Beneficial — brighter, denser growth with it
Temperature	20–28°C (tolerates cooler than most)
pH	5.5–7.5
Hardness	Soft to medium
Fertiliser	Rich micros and iron; lean nitrogen deepens colour
Substrate	Rich preferred; grows in inert with column dosing
Growth rate	Medium
Placement	Midground to background
Difficulty	Medium

Fine red texture for the midground

Its fine foliage makes arcuata unusually versatile: planted densely it forms a soft orange-red haze, and its slim profile lets it sit further forward than most background reds. It contrasts especially well with broad green leaves and rounded stems, where the difference in leaf shape amplifies the colour.

Cuttings that bush out

Top and replant like any stem; the cut stems branch readily, so a few plants quickly become a thicket. Frequent trimming keeps it dense and encourages the bushy, brightly-tipped growth that looks best.

What goes wrong

Green, not red means more light. Leggy, sparse stems with long internodes is the same message. Because the leaves are so fine, arcuata can trap debris and be prone to algae in a dirty or low-flow tank — good flow and clean water keep it looking sharp. The hybrid is not a notable melter, so persistent poor growth usually comes back to light and feeding; the true species is more likely to sulk or melt during the emersed-to-submersed transition and after parameter swings.

More plants in this series

• Ludwigia repens — the broad-leaved classic red
• Rotala wallichii — another fine-leaved pink stem
• Rotala rotundifolia — easy colour-changing stem
• Alternanthera reineckii — bold broad-leaved red