AROID REPRODUCTION

What is sold as an aroid “flower” is not one. It is an inflorescence: a dense column of many individually tiny flowers — the spadix — subtended by a single modified bract, the spathe. That is the family’s signature, and it is remarkably conserved. Every inflorescence morphology in Araceae can be read as a variation on that one theme.

Which makes the family’s reproductive diversity the interesting puzzle. A group with an almost invariant floral architecture has nevertheless produced one of the widest ranges of pollination systems in the flowering plants — beetle brood chambers, fly nurseries, carrion mimics, sweet-scented bee flowers, and at least one lineage that heats itself past 47 °C before dawn.

Why unisexual flowers changed everything

The usual explanation for that range starts with a single structural decision: in much of the family, the flowers are unisexual. Male and female flowers occupy separate territory on the same column instead of every flower carrying both sexes.

That separation did two things. It made zoning possible — and zoning, in turn, opened the door to sterile flowers. Once a stretch of the spadix no longer had to make pollen or ovules, it was free to do something else entirely. The results are the family’s specialist organs, and they are worth naming as a set because almost every aroid you will meet has some combination of them:

A barrier. Sterile tissue between the sexes that physically keeps pollen away from stigmas.

An advertising organ. A sterile terminal appendix whose job is scent, sometimes at spectacular scale — in Alocasia macrorrhizos it is 60% of the spadix and carries no flowers at all.

A furnace. Tissue specialized for thermogenesis, which volatilizes the scent and, in some species, is a reward in its own right.

A restaurant. Sterile male flowers that secrete food for the visitors — in Alocasia odora the sterile zone exudes a sugar- and amino-acid-rich liquid that is its pollinating flies’ main food — their sponging mouthparts cannot take up solid pollen.

The chamber, and the door in it

The second great innovation is the floral chamber. In many aroids the lower spathe does not open at all: it stays wrapped into a closed vessel around the female flowers. Add a constriction partway up — a waist that can tighten and relax — and the inflorescence acquires something no open flower has. It can hold its pollinator.

That is a genuine step change. An open flower gets whatever contact a visitor makes in the seconds it is present. A chamber keeps its visitors for hours or a few days, through a whole scripted sequence: attracted during the female phase, retained while the stigmas are receptive, and released only once pollen is being shed — past the anthers, on the way out.

What does the retaining varies, and the distinction matters more than it might seem. Some species hold visitors with genuine rewards — food, warmth, a mating arena, shelter from daylight. Others hold them with trap mechanisms, slippery walls and a constriction that simply shuts — and, in some genera, rings of stiff sterile flowers that work as a size filter rather than the one-way valve they are usually described as. And in some the same closing door does both at once: the constriction in Alocasia shuts on visitors already inside while excluding everything that arrives afterwards.

Female first: protogyny

Almost universally among aroids with separate sexual phases, the female phase runs first. The stigmas become receptive, the plant advertises, visitors arrive — and only afterwards does the same inflorescence release its pollen. This is protogyny, and its prevalence is striking: among thermogenic-flowered species whose sexes mature in sequence, surveyed across fifteen flowering-plant families, 70 of 71 are protogynous.

The logic is straightforward. An insect arriving at a female-phase inflorescence is arriving from somewhere else, and whatever pollen it carries is another plant’s. By the time this inflorescence contributes its own, its stigmas are — in theory — already past use. Outcrossing gets the first attempt.

The second lock: self-incompatibility

Behind the choreography sits chemistry. Where it has been tested in the family, self-pollination frequently fails outright rather than merely being made difficult. In wild Alocasia macrorrhizos, 20 strict self-pollinations and 20 crosses between plants of the same clone produced no mature seed at all — a few berries started, then stopped after about three weeks. Crosses between genuinely different plants of the same species, by contrast, took 79 times out of 88.

For anyone hoping to breed aroids, that asymmetry is the single most important fact on this page, and it reframes the whole exercise: the hard part is almost never the technique. It is having two plants that are really two plants. Divisions of one mother, or two imports from the same tissue-culture line, are one individual wearing two pots. A breeder keeps two plants apart by number: Wilbert Hetterscheid’s seed lot of Amorphophallus lewallei came from crossing his clones H.AM.020, with conical, pointed warts on the appendix, and H.AM.021, with rounded ones (Aroid-L mailing list, Wilbert Hetterscheid, September 5th, 2004).

The furnace

A number of aroids generate metabolic heat in their inflorescences during anthesis, and the range across the family is enormous. Taro, Colocasia esculenta, never exceeded 7 °C above the surrounding air. Wild Alocasia macrorrhizos reached a mean maximum of 43.9 °C against 22.4 °C ambient, with single readings to 47.8 °C and a departure from ambient of 25.6 °C. Its close relative Alocasia odora manages about 2.4 °C.

Two species in one genus, an order of magnitude apart. Thermogenic capacity is not a family-level trait you can assume from a relative.

Mechanistically the standard explanation is the alternative oxidase pathway — a respiratory route that bypasses two of the three points at which energy is normally captured, so that far more fuel has to be burned for the same return and the difference comes off as heat. In Alocasia odora a single gene, AOX1b, is switched on specifically in the heating tissue, expressed some 1,800-fold higher in the male zone than in the female zone immediately below it. The fuel, at least in the appendix, appears to be carbohydrate.

How the oxidase comes to be engaged looks like a threshold rather than a switch. In plant mitochondria it draws nothing until the quinone pool feeding it is most of the way reduced — past about 60% reduction, measured in soybean, Glycine max, rather than in an aroid — and then it climbs steeply. If an appendix works to the same threshold, the heavy substrate load is the precondition for the oxidase engaging at all rather than a by-product of it.

Expression is not necessity, though, and that is the weak joint in the standard account. Blocking the alternative oxidase in excised, chemically induced appendix sections of Sauromatum guttatum did not stop them heating under most light regimes; only after 20 hours or more of light did it suppress the rise. The level matters: in isolated mitochondria the block works. On single traces, n-propyl gallate flattened substrate-driven oxygen uptake in Sauromatum guttatum and in Arum maculatum alike. The organelle and the excised tissue do not agree, and no inhibition experiment has closed the gap. The position the reviews now take is that ordinary coupled respiration is required but not sufficient, and that what sets thermogenic tissue apart is the running of the whole respiratory route rather than that one enzyme.

Three jobs the heat does

1. It volatilizes the scent. This is the standard explanation, and the one nearly every paper on the subject assumes: warm tissue evaporates volatile compounds faster, so the advertisement carries further. The supporting evidence is that heat and scent peak together — in Alocasia macrorrhizos the temperature maximum and the moment of maximum odor coincide exactly, at 05:45–06:00. What is missing is a direct test. The heat has been stopped — a spadix sealed in nitrogen, in the 1838 experiment described below, ceased to heat and lost its smell — but nitrogen shuts down the plant’s breathing along with its heat, so it cannot show whether warmth is what carries the scent. No published study has yet blocked an aroid’s heat on its own and measured what happened to its scent, and the argument against sufficiency is strong: heating often continues for as long as the insects stay, not merely while they are being recruited, and in some species the temperature that gets defended is the one inside the chamber rather than the one at the scent organ.

The nearest thing to a test runs the experiment the other way round, and it is worth knowing because it separates the two things this job confuses. In the dead-horse arum, Helicodiceros muscivorus, the foul smell is produced only on the first of the two days the inflorescence is open; by day two it is undetectable, and visits fall away significantly. Put the missing compounds back — a synthetic blend on cotton rolls inside the chamber — and day-two plants drew as many flies as they had on day one. Odor alone restored the long-range signal. When heat was then added on top of the synthetic odor, it made no difference to how many flies arrived. So in this plant, where the two have been pulled apart in the field, the recruiting is done by the chemistry, not by the temperature — which does not refute this job, but does show that heat is not what carries the advertisement in that plant. What heat does there instead is job 3.

2. It is sometimes the reward — demonstrated once. In Philodendron solimoesense a warm chamber is metabolically valuable to its pollinating scarab, Cyclocephala colasi, which would otherwise burn its own reserves staying warm. Measured overnight in 20 inflorescences, the floral chamber ran 3.4–5.0 °C above the outside air while the beetles were active; the energy that saves them was then calculated, at between 2.0 and 4.8 times. The plant is not advertising with heat so much as paying with it. Two limits are worth carrying: no beetle has ever been measured inside a flower, and where the same question was asked of flies, the answer came back negative — the blowflies leaving a Helicodiceros muscivorus chamber were too cold to fly and warmed themselves by shivering, not by the plant. Their thoracic temperatures ran 3–5 °C above ambient on average, and the chamber air sat at 16–19 °C while the male florets were close to 25 °C — the warmth was right beside them and they did not take it. One beetle, one plant, one demonstration.

3. It steers the insect once inside. The newest and most surprising result. Because only the upper spadix of Alocasia odora heats, the inflorescence carries an internal thermal gradient that reverses between day and night — and that gradient, not scent, is what moves the flies. By day the warming top pushes them down onto the receptive stigmas; by night the still-warm top pulls them back up onto the pollen. Warming and cooling the outside of the spathe flipped the flies’ distribution from 10.4% to 89.2% in the upper chamber at noon, and from 91.4% down to 8.0% at midnight. Two thousand lux of light at night did essentially nothing.

It is no longer a single case. The same job turns up in a completely different plant, with a different pollinator and a cleaner experiment. In Helicodiceros muscivorus the appendix heat is confined to day one — the male florets heat as well, reaching 25.0–29.3 °C at maximum and 11.9–15.5 °C above the air — and that appendix heat works as a landing beacon rather than a gradient: a fly that finds the appendix is three times as likely to go on into the trap chamber than one that lands on the spathe — 33.0% against 10.2% — and 69.4% of the flies that got in came that way. Wind a resistance wire round the appendix of a second-day plant, warm it to the level the plant itself manages, and the proportion of arrivals that find the appendix climbs back from 24.0% to 39.6%, statistically indistinguishable from an untouched first day. The control matters: the same wire was fitted, unpowered, to the plants it was being compared against.

Read the two together and the job sharpens. In one plant the heat sorts the insects inside the chamber; in the other it decides how many get in at all. Neither is advertising. Both are steering an animal that has already arrived — which is a different claim from the one the textbooks make about aroid heat, and much better evidenced.

Three is not the whole list, and the ones left off it are not about insects at all. In the skunk cabbage, Symplocarpus foetidus, the heat may be what keeps the plant alive: Knutson (1974) described the spadix tissue as not frost-resistant and escaping freezing by holding a high respiratory rate, but whether the heat actually contributes to survival in the cold remains largely unknown. And in its Japanese relative Symplocarpus renifolius, whose spadices averaged 23 °C in the stigma stage (40 inflorescences in the field) with the daytime air near 11 °C, pollen germination and pollen tube growth both fall away either side of that same 23 °C — so the temperature being defended may be the plant’s own gametes’ optimum rather than anything to do with a visitor. That set point is not a single number, though: the same species sits at 17.6 °C with the air at 5 °C and at 27.6 °C with the air at 30 °C, and below 15 °C in the tissue the regulation stops altogether. Which way that runs is not yet something anyone can tell.

The smell, and what it is made of

Aroid scent spans just about the whole olfactory range available to a plant: sweet and fruity at one end, and at the other, faithful reproductions of dung, carrion and rotting fungus. The scent is the long-distance signal — the part that recruits from outside the plant — and in the appendix-bearing species where it has been traced, the sterile appendix is usually doing most of it. Scent and sight can work as a pair: in Lysichiton americanum, experiments showed that the spathe’s odor starts the beetles’ search and the exposed yellow spathe increases their landings. Where the scent tissue itself has been worked out anatomically, though, the answer comes back genus by genus: in Caladium bicolor, which has no terminal appendix at all, it is the sterile flowers that carry the fragrance, not the fertile male zone (Madison 1981). Partition an Alocasia odora spadix and offer the pieces separately and the appendix takes 67% of 847 flies, against 2.5% at the female end.

Chemistry is published for very few aroids. In Alocasia odora, nine compounds account for 94.5% of emission, six of them concentrated in the appendix: methyl propionate, methyl butyrate, methyl 2-methylbutyrate, methyl benzoate, (E)-4,8-dimethylnona-1,3,7-triene and methyl salicylate. Note what most of those are — short-chain methyl esters, the chemistry of fermenting fruit. Which is exactly what you would build if your intended audience were drosophilid flies.

And the display size matters, not just its composition. Cutting the appendix off an Alocasia odora inflorescence measurably reduced its fruit set; removing the appendix and the male zone together reduced it further. Bigger advertisement, more seed — the first demonstration in any plant that the magnitude of an olfactory display feeds through to reproductive success.

Reward, or deception

Every pollination system is a transaction, and aroids resolve it in two opposite ways. The distinction is the most useful single axis for understanding any aroid you meet.

Rewarding systems pay. The visitor gets food, warmth, shelter, a mating arena, or a place to lay eggs, and both parties profit. The Alocasia–Colocasiomyia relationship is the fully developed version: the flies feed on the sterile zone’s exudate, mate inside the chamber, lay their eggs among the pistils, and their larvae grow up inside the ripening fruit head — without damaging the fruit. Compare that to figs and fig wasps, where the plant buys pollination by surrendering seed. Here the plant pays nothing it needs. The flies are so committed that across the genus Colocasiomyia — 25 described species and some 65 still awaiting description — they are found on essentially nothing but Araceae, Arecaceae and Magnoliaceae, and one lineage breeds only on Colocasia, Alocasia and Steudnera.

Deceptive systems do not pay. Instead the inflorescence mimics the thing its pollinator is actually looking for — faeces, a fungus, a dead animal — and the insect arrives expecting a place to feed or breed and leaves with nothing but pollen. This is the strategy behind the family’s most notorious smells, and it is where Amorphophallus, Arum and Helicodiceros live. The mimicry can be good enough that insects lay eggs on it, and the larvae then starve.

For most of the family that word — mimicry — is doing more work than the evidence supports. It usually rests on a human nose and a resemblance. In exactly one aroid it has been tested properly, and the result is worth carrying because it sets the standard the rest of the family has not yet met.

The dead-horse arum’s smell was run through a gas chromatograph alongside the headspace of an actual rotting carcass, with a blowfly’s antenna wired in as the detector. Three compounds did the work — dimethyl mono-, di- and trisulfide, the chemistry of decaying protein — and the antenna responded to the flower and to the carcass no differently. On the strength of that the authors make the careful claim, and it is the right one: a carrion fly cannot separate the mimic from the model by smell alone. The flies it catches are overwhelmingly female — 78% at the flower and 100% at the carcasses — which is what the mimicry predicts, since it is the females that need somewhere to lay.

Three honest limits. Those three compounds are the ones the antenna reacted to, not the plant’s whole bouquet, and “no different” is a failure to find a difference on eight runs rather than a proof of identity. The visual half of the resemblance — the hairy spathe, the dark opening the authors describe as an illusion of a rectal opening complete with a tail — has never been tested at all. It is a photograph and a caption, not a result. And the chemistry rests on very little material: the study that first identified these compounds worked from a single cultivated plant in a glasshouse, sampled twice, which could not even be bagged because it was on public display.

The same seven questions, across thirteen genera

The genera this hub covers, answered as far as the literature allows. Where a cell is thin, the thinness is the finding — it says how little of this family has been watched at the flower.

What actually visits an aroid

Across the world’s thermogenic flowers — the group aroids dominate — the pollinator records break down as 70.1% beetles, 32.2% flies and 4.6% thrips, out of 87 species with data. (The percentages exceed 100 because a species can have more than one.) Bees barely feature, and where they do appear they are often taking rather than pollinating: in Alocasia macrorrhizos, stingless bees and honeybees turned up in numbers to collect pollen and contributed essentially nothing: the stingless bees came mostly after the chamber had closed and rarely reached the stigmas, and honeybees were judged too large to enter it.

That is the pattern to hold onto. Aroids are overwhelmingly a beetle-and-fly family, and their pollinators are specialists that live on the plant rather than generalists passing through. Colocasiomyia — 25 described species and some 65 more awaiting description — occur on essentially nothing but Araceae, Arecaceae and Magnoliaceae, and one lineage breeds only on Colocasia, Alocasia and Steudnera. Cyclocephaline scarabs have a comparably tight relationship with Philodendron.

What this means if you want to breed them

The seven questions are not academic. Two of the answers change your technique outright.

Question 1 decides how you get access. With bisexual flowers — Anthurium, Monstera — the whole spadix is exposed and there is nothing to cut: you brush it. With unisexual flowers inside a closed chamber — Alocasia, Philodendron, Amorphophallus — the stigmas are sealed in a tube and every technique is some answer to reaching them. That is a fundamentally different job, and it is why a guide written for Anthurium can mislead you badly on an Alocasia.

And pollen does not behave the same way across the family. Alocasia pollen handles as dry, though fresh from the anthers it can be sticky and clumped. Philodendron and Caladium shed moist, stringy pollen, and long-term freezing of those is expected to fail, while Alocasia pollen is binucleate, the cell type expected to store. So the freezer trick that bridges the protogyny gap in one genus may simply not be available in another.

Beyond that, the constants hold across the family: female phase first, outcross pollen strongly preferred, and the real bottleneck being two genuinely unrelated plants in flower near enough in time to use each other.

Which leaves the question this section cannot answer: unrelated by how much, and can two plants be too far apart to work? A cross between plants with different chromosome numbers will often still set seed, and that seed will often still grow — and the plant it becomes may then be unable to make working pollen of its own. A mismatch does not usually stop a cross; it stops the generation after.

What is known about where those limits fall is gathered in Why Some Crosses Fail. The short version is that no aroid genus has a compatibility matrix you can look any two of its species up in — one genus has a breeder's record of what failed, one has a map of what succeeded, one has chromosome counts and a crossing program scored by morphological group, one has a single intersectional cross tabulated at cultivar level with every rate and denominator printed. Outside those four genera the record is not empty: a Cryptocoryne program crossing species from Borneo made a hundred and ninety-eight attempts, of which fifty-six set fruit and seventeen gave flowering plants.

Seed in hand still leaves a long wait before the seedlings can be crossed in turn, and the wait is uneven. Two Amorphophallus abyssinicus flowered in the right sequence in the summer of 2004, a grower signing as Dewey reported, and hand-pollinating the second inflorescence gave seed and fruit; by January 31st, 2005, most of the seedlings were starting a second juvenile leaf (Aroid-L mailing list, Dewey, January 31st, 2005). Flowering takes longer. Of twelve Amorphophallus titanum seedlings Kathy Upton planted in February 1995, one opened a miniature inflorescence about two feet tall three years and three months later (Aroid-L mailing list, Kathy Upton, April 20th, 1998; Aroid-L mailing list, Kathy Upton, April 27th, 1998; Aroid-L mailing list, Kathy Upton, April 29th, 1998; Aroid-L mailing list, Kathy Upton, May 4th, 1998), and a second plant from the same seed batch flowered six years and four months after planting (Aroid-L mailing list, Kathy Upton, June 13th, 2001; Aroid-L mailing list, Kathy Upton, June 20th, 2001). A single Amorphophallus titanum, the one survivor of three or four seeds received at Inhotim Botanical Garden in Brazil in 1999 or 2000, flowered about ten years from seed (Aroid-L mailing list, Eduardo G. Gonçalves, December 17th, 2010), and a greenhouse juvenile that its grower named as Cyrtosperma cuspidispathum was in bloom about three years from seed (Aroid-L mailing list, Michael Mattlage, June 28th, 2007). Each is one grower’s report, not a measured trial.

You can read the rest of the site without this section. It is here for the moment a sentence stops making sense — and because the single biggest barrier to a grower publishing what they have seen is not the observation, it is the fear of using the wrong word for it.

The parts you are looking at

Inflorescence

The whole flowering structure, not a single flower. When people say an aroid “flower” this is almost always what they mean, and it is the reason this site avoids the word.

Spadix

The central column, carrying dozens to thousands of tiny true flowers. say: SPAY-dix · plural spadices

Spathe

The hood, cup or blade wrapped around the spadix. It is a modified leaf, not a petal, which is why it is so often green on the outside. say: SPAYTH

Appendix

The sterile tip of the spadix, above all the flowers — the bare spike in an Amorphophallus, the smooth club in an Alocasia. It carries no flowers at all and exists to advertise: it is usually the part that heats, and usually the part that smells.

Staminate and pistillate

Male and female. In most of the genera on this site the two are in separate bands on the same spadix — female at the bottom, male above — and knowing which band you are looking at decides where you cut and where you put the pollen.

Constriction

The waist where the spathe pinches in between the female and male zones. It is the door: when it is open the chamber can be entered, and when it tightens, whatever is inside stays inside.

Floral chamber

The sealed space below the constriction, containing the female flowers. In many aroids this is where the entire transaction happens, out of sight.

Staminode · synandrode · synandrium

Sterile male structures. A staminode is a stamen that has stopped making pollen and taken up another job — feeding the visitors, blocking the passage, making scent or making heat. A synandrium is several stamens fused into one unit, which is why an Alocasia male flower looks like a single button rather than a ring of anthers; a synandrode is the sterile version of that.

Anther · dehiscence

The anther is the part that holds pollen; dehiscence is the moment it opens and lets it go. “Anthers dehisce on day two” simply means the pollen appears on day two.

Stigma · style · ovary · ovule

The female chain, from the outside in. Pollen lands on the stigma, grows down through the style, and fertilizes an ovule inside the ovary. One fertilized ovule becomes one seed, which is why counting ovules tells you the most seed a berry could ever hold.

Peduncle

The stalk holding the whole inflorescence up.

Infructescence

What the inflorescence becomes once the berries form — the fruit head.

Corm · tuber · offset · division

The underground storage organ and the ways it multiplies. An offset is a new plant budded off the parent; a division is one you cut apart yourself. Both matter here for an uncomfortable reason: neither is a new individual.

Cataphyll

The papery sheath that wraps a new shoot before it opens. Useful as a timer — it often tells you something is coming before you can see what.

The clock

Anthesis

The flowering event itself — the hours or days when the inflorescence is actually open and functioning, as opposed to merely present. In many aroids the whole of anthesis is over in 24 to 48 hours, which is why timing dominates this subject. say: an-THEE-sis

Receptive · receptivity

The window when a stigma can still accept pollen and do something with it. A stigma that looks fine may be long past it, and this is the single most common reason a hand cross fails.

Protogyny

Female first. The stigmas mature and are ready before the same inflorescence releases its own pollen — nearly universal in this family, and the reason a single plant usually cannot pollinate itself. say: pro-TOJ-in-ee · adjective protogynous

The heat

Thermogenesis

The plant making its own heat, deliberately, by burning stored fuel in its flowering tissue. Some aroids run more than twenty degrees above the surrounding air; a quarter of one large genus does not do it at all. say: ther-mo-JEN-e-sis · adjective thermogenic

Thermoregulation

Not the same thing, and constantly confused with it. Thermogenesis is making heat; thermoregulation is defending a set temperature against the weather — producing more heat as the night cools, and never absolutely: the defended temperature itself drifts, and it has a floor. In Symplocarpus renifolius the regulation stops altogether below 15 °C in the tissue. Most aroids do the first. Very few do the second.

Alternative oxidase

The usual explanation for it: a respiratory pathway that bypasses two of the three points at which energy is normally captured, so that much more fuel has to be burned for the same return and the difference comes off as heat. It is the standard answer to how an aroid runs a fever without a muscle — but blocking it in a living plant did not stop the heating, and it is one of at least two routes described in this family, so it is not the whole answer.

Uncoupling protein

The second of those routes, and a different lesion. The alternative oxidase bypasses the points at which energy would have been captured; an uncoupling protein lets the gradient the mitochondrion has already built leak back across its membrane. In Philodendron selloum the message that climbs with the heat is an uncoupling protein’s, about tenfold up in the heating tissue, while the alternative oxidase’s is present in every tissue examined and moves far less; in Dracunculus vulgaris it runs the other way round. Both patterns sit inside this one family, and which one an aroid uses is not predictable from its relatives.

The smell

Volatile

Any compound light enough to evaporate and travel through air. A “scent profile” is just the list of volatiles a flower emits and their proportions.

Osmophore

The specific tissue that manufactures and releases the scent. It is usually somewhere on the appendix — but in at least one genus it turned out to be the fertile male flowers instead, so it is worth asking rather than assuming. say: OZ-mo-for

The bargain

Reward · deception

The two ways a flower can get an insect to work for it. A rewarding system pays — food, warmth, shelter, a place to breed. A deceptive one imitates something the insect wants, usually dung or carrion or fungus, and delivers nothing.

Brood site

A place an insect lays eggs and its larvae grow up. Some aroids genuinely provide one, which is about the strongest bond a plant and an insect can have; deceptive ones only pretend to, and the larvae die.

Mutualism

An arrangement where both sides come out ahead. Worth keeping separate from “pollination” in general, because plenty of pollination is not mutual at all.

Making seed

Self-incompatibility

A plant's built-in refusal to accept its own pollen — a chemical rejection, not a timing problem. It is why some crosses can never work no matter how well you time them.

Clone

Genetically one individual, however many pots it occupies. Two divisions of one plant, or two imports from the same tissue-culture line, are a clone — and crossing them is a self, with all the failure that implies.

Fruit set · seed set

The proportion of flowers that go on to make fruit, or seed. It is the number that tells you whether a pollination actually worked, and the one most often missing from the literature.

Viability

Whether pollen is still alive enough to germinate, or a seed still alive enough to sprout. Pollen viability in this family is measured in days, not weeks, and often falls by half within 24 hours.

Apomixis

Making seed with no fertilization at all. Rare, but worth knowing about, because it can produce a berry full of seed that looks like a successful cross and is genetically just the mother. say: ap-o-MIX-is · adjective apomictic

Raphides

Bundles of needle-shaped calcium oxalate crystals in the tissue. They are the needles that carry the sting, and why gloves are advised — though they are not the whole of it, and the chemistry behind aroid irritancy is not settled. They are also widely said to protect the seed — and when someone finally sectioned twenty-one species to check, the ovules themselves turned out to be crystal-free. It is the wall around them that is loaded. say: RAF-id-eez

Who turns up

Insect family names look forbidding and mostly are not. The endings are regular: -idae means a family, -inae a subfamily. The ones that recur here, in plain terms:

Drosophilidae — the vinegar flies

Small flies most people know from overripe fruit. Colocasiomyia, the genus that pollinates Alocasia and Colocasia, is one of these.

Nitidulidae — sap beetles

Small, flattened beetles that feed on sap and fermenting matter. They turn up inside a surprising number of aroids.

Staphylinidae — rove beetles

Narrow beetles with strikingly short wing cases, so most of the abdomen is exposed.

Cyclocephaline scarabs

Heavy, blunt, nocturnal beetles — the ones that spend the night inside a Philodendron. Large enough that a warm chamber is worth real energy to them.

Psychodidae — moth flies

Tiny, furry, moth-like flies that breed in wet decaying matter. The classic Arum captives.

Anthomyiidae — root-maggot flies

House-fly-like in build. Named as the pollinator of at least one Alocasia, which is a reminder that the fly story in that genus is not finished.