Alternanthera reineckii: red colour that actually stays red
Most plants that claim to be red turn out to be brown. Alternanthera reineckii delivers genuine magenta and carmine — if you understand what drives the colour.
Where it comes from
Alternanthera reineckii is a South American stem plant native to the wetlands, river margins, and flooded grasslands of Brazil, Paraguay, Uruguay, and Argentina. It belongs to the Amaranthaceae family and grows both as an emergent plant (leaves above water) and fully submerged. The red and purple pigmentation that makes it so attractive in the aquarium is present in the submersed form primarily in the leaf undersides and, under high light, across the upper surface as well.
It was introduced to the aquarium hobby in the 1970s and has been one of the core red stem plants ever since — partly because of its reliable colouration, and partly because the compact variety (AR Mini) became a staple of the Dutch aquascape style, where it is used to create distinct colour zones in planted layouts.
What to expect
Leaves are lanceolate (elongated, tapering at both ends), typically 3–6 cm long in the standard form, with a rich pink to carmine-red undersurface and a green to reddish-brown upper surface depending on light intensity. The stems are reddish and upright, reaching 30–50 cm before trimming in the standard form.
AR Mini (sometimes sold as Alternanthera reineckii 'Mini') is the compact variety most commonly kept today. It has smaller leaves (1–3 cm), grows more slowly, stays lower, and produces a more intense magenta-red colour. It is generally the more practical choice for small to medium aquascapes.
AR Rosaefolia has a brighter rose-pink tone rather than the deeper red of standard plants. AR Lilacina shows lilac and purple tones on the undersurface. Both are less commonly traded but available from specialist suppliers.
How to keep it
| Parameter | Value |
|---|---|
| Lighting | High — colour intensity increases directly with light; grows green in low light |
| CO2 | Beneficial — enables faster growth and supports higher light levels; not strictly required |
| Temperature | 22–28°C |
| pH | 5.5–7.5 |
| Hardness | Soft to moderately hard (2–15 °dH) |
| Fertiliser | Regular macro and micro dosing; lean nitrogen promotes deeper red colour |
| Substrate | Nutrient-rich aquasoil preferred; standard gravel works with water-column fertilisation |
| Growth rate | Moderate — slower than most stem plants; AR Mini slower still |
| Placement | Midground, Background |
| Difficulty | Medium |
What actually drives the red colour
The red and purple pigments in Alternanthera reineckii are anthocyanins — the same class of pigment found in red cabbage and autumn leaves. Anthocyanin synthesis is triggered primarily by high light intensity; CO2 helps indirectly by allowing the plant to use that light efficiently. Nutrient balance also matters: lean nitrogen (keeping nitrate relatively low) tends to intensify red colouration, while excess nitrogen pushes the plant toward greener growth. Increase light first if the plant is losing colour; if already bright and green, check that nitrate is not elevated well above 20 ppm.
Where it works best
Alternanthera reineckii is used almost exclusively as a colour accent against green plants. Its red and magenta tones stand out most clearly when placed behind or adjacent to bright green plants with contrasting leaf shapes — the fine texture of Rotala rotundifolia, the broad leaves of Amazon sword, or the feathery outline of water wisteria all provide a strong contrast.
AR Mini works best in the mid to lower-midground of aquascapes between 40–60 cm wide. The standard form suits larger tanks where it can grow to full height as a background accent. In Dutch-style aquascapes it is used in distinct "plant streets" — solid columns of a single species — where its colour creates a focal point against the surrounding greens.
Avoid placing it in the deepest part of the tank where it will receive the least light; the red colour fades quickly in shaded positions regardless of other parameters.
How to propagate
Side shoot trimming is the standard method. Cut the top 5–8 cm of a stem, remove the lowest pair of leaves, and plant the cutting. Roots develop within 10–14 days. The parent stem will branch from the cut node, producing 2–3 new shoots. Unlike faster-growing stems, Alternanthera reineckii takes 2–3 weeks to fully establish cuttings rather than days.
What goes wrong
Leaves turning green. Insufficient light is the primary cause. Increase light intensity. High nitrate can also suppress red pigmentation — if light is adequate, check that nitrate is not elevated above 20 ppm.
Slow growth, purple-black colouration. This extreme dark colouration can look attractive but usually indicates the plant is stressed rather than thriving. Most often seen in very soft water or very low CO2. Stable parameters and adequate CO2 produce the clearest, brightest red.
Lower leaves yellowing and dropping. Normal as the stem elongates — the lower leaves lose light. Trim and replant top cuttings regularly. Grouping three or more stems together helps maintain density as individual stems age.
Algae on leaves. Slow growth makes leaves susceptible to algae settling. Ensure adequate flow across the plant and maintain CO2 stability to keep growth active enough that algae cannot gain a foothold.
More plants in this series
- Rotala rotundifolia — the colour-shifting stem plant
- Ludwigia repens — easy red without CO₂
- Tiger lotus (Nymphaea zenkeri) — the statement bulb plant
- Water wisteria (Hygrophila difformis) — the shape-shifting stem plant
- Hygrophila polysperma — the ultra-reliable beginner stem