Alocasia nebula

Where it comes from

Borneo, probably Sarawak — and the hedge is Kew’s, not mine. The POWO record says “Borneo (Sarawak)” flatly,¹ but IPNI, from the same institution and working from the description’s own data, prints it with a question mark: “Borneo (Sarawak)?”.² When Kew’s two databases disagree about whether they know where a plant is from, the honest answer is the one with the question mark.

The reason for the doubt is that the plant science named was growing in a glasshouse. The type was collected on 30 April 1999 by Alistair Hay himself, from the living collections of the Royal Botanic Garden Sydney, accession 980858.² A garden bed in New South Wales is the origin of record for a Bornean species — which tells you something about how this plant reached botany, and something about how thin the field data is.

The habitat, such as it is, is reported as rain-forest floor over limestone at low elevation.³ Take that as substance rather than as a quotation: it appears on one specialist page outside anything marked as the original description, and it is absent from Kew. The pattern itself is real enough in the genus — Bornean Alocasia do include a run of limestone specialists⁴ — but no wild collection of this one has ever been reported, so there is nothing to confirm it against.

Note what “over limestone” would mean if true: the plant sits in forest floor litter lying on the rock, not in it. Karst holds a thin soil that drains almost instantly into the stone beneath.⁵ That argues for an airy humus mix that never stays wet — the opposite of the “so add lime” conclusion the phrase usually gets.

Naming and description

Alocasia nebula A.Hay, published in Curtis’s Botanical Magazine 17: 16 (2000), with a colour plate.¹² No synonyms.

Nebula is mist, cloud, vapour — and it fits twice over. The leaf does look like something drifting; and the plant’s own origin was unclear from the start, which is exactly what a type specimen from a Sydney glasshouse and a question mark after “Sarawak” amount to. A specialist reference states the double meaning outright;³ I could not reach the description to confirm the words are Hay’s, so the pun is offered here as a reading rather than as a quotation.

On colour, the trade oversells and the description undersells in the useful direction: the upper surface is matt grey green rather than blue or pewter, and the underside is dark reddish purple. The blade is strongly coriaceous and bullate between the veins, with 5–7 primary lateral veins each side and a conspicuous submarginal vein running about 2 mm inside the edge — that last one is visible without a lens and is the best single check on a label.³

It is small: a herb of about 20–30 cm carrying around six leaves, on petioles of about 15 cm, with a blade roughly 23–24 cm long overall.³

Two names to be careful with. ‘Elaine’ is sold as a cultivar of this species, but the specialist sources disagree about whether it belongs to nebula at all — one places it under Alocasia reginae, a separate accepted species⁶ — and another says flatly that plants sold as ‘Elaine’ or ‘Imperialis’ are simply A. nebula.³⁷ ‘Imperialis’ is worse: it is a recycled botanical name that Kew places in the synonymy of Alocasia scabriuscula, a different species again.⁸

Fun facts

• The name is a joke about not knowing where it came from. Nebula for the clouded leaf, and for a plant whose provenance was a blank — a type gathered from a botanic garden bed, a range Kew’s own index queries, and not one reported wild collection in the twenty-five years since. It is the rare species epithet that documents the state of the evidence.
• Grey-blue leaves are usually wax over dark tissue, not pigment — and light changes them. The clean demonstration is on a cycad: the blue-grey comes from crystalline wax scattering over chlorophyll-rich tissue beneath.⁹ Alocasia leaves do carry measurable cuticular wax that does real work,¹⁰ and in Hosta the wax responsible fell from 47.1 to 9.1 mg·dm⁻² as light rose, so shade keeps the bloom and strong light burns it off.¹¹ Two cautions: nobody has studied this species’ leaf surface, and Hay called it matt grey green rather than glaucous — so the bullate surface may be doing the work on its own. Testable at home, which is the point.
• The failure mode is named in the description. It has a reputation as the hardest Alocasia, and the single citation behind that is one grower’s opinion.¹²¹³ What is on the record is more specific and more useful: the plant is prone to sudden collapse, especially if the roots become too cool and waterlogged.³ Cold wet roots, not light and not feeding. That is an actionable sentence in a way that “difficult” is not.