Oxalis vulcanicola Donn.Sm.

Where it comes from

Central America: Costa Rica, El Salvador, Guatemala, south-east Mexico and Panama.¹ Vulcanicola means volcano-dweller, which is where it grows.

Naming and description

The name on the label is the wrong plant. This is sold as Oxalis spiralis ‘Aurea’, and Oxalis spiralis is a real accepted species — but a South American one, from Argentina, Bolivia, Colombia, Ecuador, Peru and Venezuela, sharing only Costa Rica with this plant’s range.² They are different species with near-disjunct distributions.

The confusion has a traceable source. Oxalis spiralis subsp. vulcanicola was published in 1980 — but Kew treats that name as a homotypic synonym of Oxalis vulcanicola Donn.Sm. (1897), which stands as its own accepted species.³⁴ Kew’s three accepted subspecies under O. spiralis are subsp. spiralis, subsp. trichophora and subsp. membranifolia; vulcanicola is not among them.² So the trade name preserves a subordination that was undone.

‘Aurea’ is a trade name and could not be anything else, because there is no International Cultivar Registration Authority for Oxalis at all — no registry exists to register with.⁵ Justia returns no patent for it.⁶⁷ Of the other names this plant travels under, ‘Zinfandel’ and ‘Molten Lava’ are trademarks;⁸⁹ ‘Copper Glow’ and ‘Sunset Velvet’ have nothing behind them beyond database entries that at least share a common name, which is consistent with their all being one plant.¹⁰

One trap worth naming. The spelling wanders between ‘Aurea’ and ‘Aureus’ — and Oxalis aurea Schltr. is a real accepted species, a South African tuberous geophyte.¹¹¹² That is precisely the opposite kind of plant to this one in the way that matters most, which the next section explains.

Fun facts

• A collapsing golden oxalis is dying, not resting — and the usual first-aid makes it worse. Many Oxalis retreat into a tuber and want to be left dry until they return. This one has no storage organ to retreat into: Kew’s lifeform field calls it a subshrub, against “tuberous geophyte” for the shamrocks people buy in spring.¹¹³ So the standard advice for a wilting oxalis — cut back on watering and wait for new growth¹⁴ — is correct for a tuberous species and fatal for this one.
• The leaves fold on the same kind of hinge the prayer plants use, evolved separately. Both move their leaves with a pulvinus, a hydraulic joint driven by potassium and water moving in and out of its cells.¹⁵ Oxalis and Marantaceae are unrelated families; the same mechanical solution turned up twice.
• The toxicity is real chemistry and badly overstated in practice. The genus is named for oxalic acid and does contain it. But NC State rates severity Low with no documented cases in humans, and Clemson calls it only mildly toxic.¹⁶¹⁷ Published figures put a minimum fatal dose of oxalic acid at 4-5 g, which at spinach-like concentrations works out to somewhere around a kilogram of leaves.¹⁸ Nobody is eating that by accident.
• No extension service has an entry for this plant at all. NC State’s plant toolbox returns “we couldn’t find any plants using the term ‘oxalis vulcanicola’”.¹⁹ The care above is inherited from the genus, and that is worth knowing rather than hiding.