Oxalis Triangularis vs Regnellii: What’s the Difference

Oxalis triangularis and Oxalis regnellii are the same species.

Regnellii is the older botanical name, now used mostly for the green leaved form, while triangularis describes the purple leaved cultivars sold as purple shamrock.

Both need bright indirect light, well drained soil, and a dry dormant period each year. Confusing the names leads to the wrong light setup.

You bought a little pot labelled Oxalis regnellii. You brought it home and started searching for care advice. Almost every result talks about Oxalis triangularis instead.

It shows the exact same plant, just with a different name attached. It feels like you bought the wrong thing. Or worse, that nobody selling these plants agrees on what to call them.

Here is the good news. You almost certainly bought the right plant. This naming mix up trips up more buyers than anything else about this houseplant.

Plant taxonomy changed faster than garden centres could keep up, and the old names never fully disappeared.

Once you understand what actually separates these two names, choosing the right form for your home gets much easier.

Quick Answer: Are Triangularis and Regnellii the Same Plant

Yes, in almost every case. Oxalis triangularis and Oxalis regnellii refer to the same species of false shamrock. Regnellii was the original scientific name.

Triangularis later became the accepted botanical name for the species.

In everyday plant shop language, the two names now do slightly different jobs. Regnellii usually points to the plain green leaved form.

Triangularis usually points to the purple leaved cultivars, especially the popular Atropurpurea.

The Naming Confusion Explained

This confusion has a real history behind it. Botanists first described this South American wood sorrel as Oxalis regnellii.

Later research folded regnellii into a wider species called Oxalis triangularis, treating regnellii as a synonym rather than a separate species.

Nurseries did not update their labels at the same pace. Many growers, especially in the United States, kept using regnellii on tags for decades.

That habit is still common today, particularly for the green leaved plants.

The purple leaved form picked up its own added name, Atropurpurea, which simply means dark purple.

You will sometimes see it written in full as Oxalis triangularis subsp. papilionacea Atropurpurea, or just shortened to purple shamrock.

Here is the part most guides get wrong. They present regnellii and triangularis as two different species with different needs.

In practice they are one species with cosmetic variation between named forms.

Treating them as botanically distinct just creates unnecessary confusion when you are hunting for accurate care advice.

Leaf Colour and Appearance Differences

The most obvious difference is colour, and it comes down to pigments called anthocyanins.

Purple leaved plants produce high levels of anthocyanin throughout the leaf tissue. Green leaved plants produce very little.

Anthocyanins do more than look attractive. They act as a natural sunscreen, absorbing excess light energy before it can damage the leaf cells.

This is one reason purple leaved Oxalis often tolerates slightly brighter positions than the green form without scorching.

Both forms share the same triangular, clover like leaflets that fold shut at night and reopen in daylight.

This movement is called nyctinasty, and it happens equally in both colour forms.

If your plant stops folding its leaves at night, that points to a light or stress problem, not to which name it goes by.

Care Differences Between the Two Forms

Care for both forms is almost identical. The differences that do exist are small but worth knowing, especially around light and dormancy.

When your Oxalis dies back for its rest period, resist the urge to throw it out. This is completely normal for both forms.

If you are starting from bulbs rather than a potted plant, our guide to planting purple shamrock bulbs walks through depth, spacing, and timing.

Popular Cultivars and Varieties

Beyond the basic colour split, several named cultivars turn up in shops and online. Knowing these names helps you buy exactly the plant you want instead of guessing from a small photo.

If you have settled on the purple leaved Atropurpurea, our full purple shamrock plant care guide covers feeding, repotting, and encouraging a fuller clump.

Common Mistakes When Choosing Between Them

Assuming the two names mean different care needs is the most common mistake.

New growers sometimes search separately for regnellii care and triangularis care, then panic when the advice looks contradictory.

It usually is not. It is simply written by different authors using different names for the same plant.

Another common mistake is buying based on a small nursery photo. Purple leaves darken with more light and stay a duller purple green in low light.

A plant that looked pale in the shop can turn a much richer purple once it settles into a bright windowsill at home.

A third mistake is panicking during dormancy. Both forms drop all their leaves and look completely dead for several weeks each year.

Growers who assume the plant has died sometimes throw away perfectly healthy bulbs.

If your Oxalis has gone bare and you are not sure whether it will come back, our guide on why a purple shamrock is dying explains how to tell true decline from normal dormancy.

Which One Should You Choose

If you want colour impact and a plant that reads as a real statement piece, choose the purple leaved Atropurpurea form.

Its deep colour holds up well on a bright windowsill and pairs strikingly with pale pink summer flowers.

If your space only offers moderate light, or you prefer a softer look, the green regnellii form is the better pick.

It tolerates lower light without stretching or fading the way purple forms can.

Neither form is genuinely harder to grow than the other. The choice comes down to colour preference and the light your home actually offers, not plant difficulty.

Both forms propagate the same way, by dividing the small bulbs during dormancy. Our full guide on how to propagate purple shamrock covers the exact timing and method step by step.

Frequently Asked Questions

Is Oxalis triangularis the same as Oxalis regnellii?

Yes, they are the same species. Regnellii is the older scientific name, now used mostly for the green leaved form.

Triangularis is the currently accepted botanical name and is commonly linked to purple leaved cultivars like Atropurpurea.

Buying either name will not get you a different species.

Why do some sellers call it purple shamrock and others call it false shamrock?

Purple shamrock usually refers to the dark leaved cultivars, especially Atropurpurea.

False shamrock is a broader common name covering the whole species, including green forms.

Both terms describe Oxalis triangularis or regnellii depending on which scientific name the seller prefers.

Neither name signals a different plant or different care.

Does the purple form need more light than the green form?

The purple form tolerates slightly brighter light better than the green form, thanks to its anthocyanin pigments.

It does not strictly need more light to survive. It does need reasonably bright indirect light to keep its deep purple colour, since low light causes the purple to fade toward green.

Why is my Oxalis losing all its leaves?

Both the green and purple forms go dormant for six to eight weeks most years, usually after flowering.

During dormancy the plant drops its leaves and looks completely dead above the soil. This is normal, provided the bulb underneath still feels firm.

Leaf drop outside the usual dormancy window, combined with soft or mushy bulbs, points to overwatering instead.

Is Oxalis triangularis toxic to cats and dogs?

Yes, both colour forms contain oxalic acid in their leaves and stems. Small amounts of contact are rarely serious for people.

Pets that eat a larger quantity can show vomiting, drooling, or lethargy. Keep the plant out of reach of pets and contact a vet if these symptoms appear.

Can I grow Oxalis regnellii and triangularis together in the same pot?

Yes, and many growers do exactly this for contrast. Since they share identical light, water, and soil needs, mixing the green and purple forms in one container causes no conflict.

Watch that the more vigorous form does not crowd out the other over a full growing season.

Why did my purple shamrock turn green?

This almost always comes down to insufficient light. Anthocyanin production, the pigment behind the purple colour, depends on strong light exposure.

A plant moved to a dimmer spot will gradually produce greener new growth.

Moving it back to a brighter position, away from direct hot midday sun, should restore the deeper colour over several weeks.

How do I know if I am buying the plant I actually want?

Look at the leaf colour in person or in a clear photo rather than relying on the label alone.

A green leaved plant sold as either regnellii or triangularis will stay green. A purple leaved plant sold under either name will stay purple.

The scientific name tells you far less than the leaf colour you can actually see.

For a wider check on plant health, our guide to fixing common oxalis problems covers drooping, yellowing, and poor flowering.

Key Takeaways

1. Oxalis triangularis and Oxalis regnellii are the same species, not two different plants.
2. Regnellii is the older name, now mostly used for the green leaved form.
3. Triangularis is the accepted name, commonly linked to purple cultivars like Atropurpurea.
4. Purple leaves come from anthocyanin pigments, which also give slight extra sun tolerance.
5. Both forms need identical light, water, and soil, so care advice for one applies to the other.
6. Total leaf drop for six to eight weeks is normal dormancy, not plant death.
7. Both forms are mildly toxic to pets, so keep them out of reach.
8. Choose based on colour preference and your available light, not on plant difficulty.

Final Thoughts

That confusing plant tag you started with makes a lot more sense now. Regnellii and triangularis were never rival plants competing for your attention.

They are two names for the same adaptable little shamrock, shaped by decades of botanical reclassification that nurseries never fully caught up with.

Once you stop treating the names as a choice between two species, choosing gets simple. Pick the leaf colour you actually want, give it bright indirect light, and let it rest when it asks to.

For background on the species itself, the RHS plant profile for Oxalis triangularis is a reliable reference for hardiness ratings and flowering habits.