THE ARISAEMA
INFLORESCENCE

The plant most English speakers know it by is jack-in-the-pulpit — Arisaema triphyllum in the broad sense, a perfectly ordinary-looking woodland herb of eastern North America. The hood over the spadix reads as shelter. It is not shelter. It is the lid of a pitfall, and the resemblance to a carnivorous pitcher plant is close enough that the same review paper draws Arisaema and Sarracenia side by side and calls it convergence — two lineages arriving at the same trap for opposite reasons. The pitcher plant catches insects to eat them. Arisaema catches them to move pollen.

How much this rests on, said plainly

The genus has 224 accepted species. Detailed pollinator data exist for fourteen of the fifty-three species native to Japan, for nine species sampled across Nepal in the survey that established the mechanism, for one species in Quebec watched through a whole season, and for four Chinese species in work published in 2025. Beyond those the record is scattered: older field notes from India, among them Edward Barnes’s on the Nilgiri species in the 1930s, and plants grown in European botanical gardens. The African group of eight species, stranded on mountains in Ethiopia, Uganda and Tanzania, has had no pollination study at all.

Section Clavata has a single study: at two populations of Arisaema heterocephalum subsp. majus on Tokunoshima, fungus gnats (Sciaridae and Mycetophilidae) dominated the trapped visitors, and the authors inferred that these gnats are its main pollinators — probably the first pollinator report for the section.

That is thin coverage for a genus this size. It is also, for a trap this strange, remarkably good: Arisaema has been under continuous investigation since the 1920s, and the last four years have produced more new mechanism than the preceding eighty.

The parts, from the top down

The hood arches over the entrance. It keeps rain out of the chamber — the same job the lid of a pitcher plant does, for the same physical reason: wet pollen is wasted pollen. In many species it tapers into a thread that hangs down toward the ground.

The appendix is the scent organ. It is the part that does the advertising, and in most species it is not even visible from outside; the smell reaches the gnat, the shape does not. Its base is often abruptly swollen or flared out like a small umbrella, and that flare matters later — where it is present, a gnat that falls past it cannot climb back up.

The tube is the prison. Its inner wall, and the surface of the spadix inside it, are coated with a microscopic wax bloom. This is the single most important structure on the page, and Part II is about nothing else.

The flowers sit at the bottom, below the appendix. In most of the genus an individual plant carries either male flowers or female flowers, never both — and which one it carries this year is not fixed. That is Part V.

The window. The lowest zone of the tube is a band of translucent tissue that lets light in from outside. In a male inflorescence it illuminates the place where the pollen has collected and where the exit is. In a female inflorescence it illuminates nothing but a dead end.

One thing the trap is not

There is no floral chamber here. In Arum, in Alocasia, in Xanthosoma, the spathe pinches shut above the flowers to seal a closed room. Arisaema has no such constriction: the tube is open all the way up to the mouth. The gnat is not sealed in. It is simply somewhere it cannot climb out of — which, for an insect of this size, is the same thing.

Scanning electron micrographs of the tube wall show the rodlets standing on the epidermis; micrographs of a mycetophilid’s foot, recovered from a spathe, show its bristles clumped and fouled with the same particles. In some species the wax is reinforced by zones of overlapping downward-pointing papillae, which make the surface not just frictionless but directional.

Why this one fact explains the rest of the page

Compare the trap next door. Arum maculatum holds its flies overnight behind a palisade of sterile bristles, and in the morning those bristles wither. The prison unlocks itself on a schedule, and the flies walk out the way they came in. The whole design depends on a moving part.

A wax bloom has no moving part. It cannot wither, retract, or be stood down at dawn. Once the wall is waxed it stays waxed for the entire anthesis — which in this genus runs for weeks, not a night. So a plant built this way has exactly two options: keep its pollinator forever, or grow a second opening somewhere else.

Which leaves the females. A female inflorescence has no pollen to give away and no reason to spend tissue on a door. It keeps the wall and skips the workaround — and the gnat inside it dies of a design decision made somewhere upstream, about wax.

The first person to describe it was Edward Barnes, working on the Nilgiri Hills of southern India, who wrote that at the bottom of the tube “where the edges overlap, the two edges arch away from one another, so as to form a small roundish orifice about 1–2 mm” — and noted, in the same breath, that female spathes have nothing of the kind. In the female the outer edge is thickened instead, and presses down harder on the inner one.

Seventy years later that observation was checked across the genus. The hole was confirmed by direct examination in ten species, and read off published photographs in fourteen more — something on the order of two dozen species spread across six sections of the genus. Given how uniformly the spathe is built, the one-way system is safe to call a general feature.

Three species that break the rule, and what they prove

Arisaema tortuosum is the important one. It is monoecious — male and female flowers on the same spadix — and it is protogynous, so its female phase runs first. In cultivated plants the exit stayed shut for the whole of the female phase and began to gape only when pollen release started. The door is not on a timer counting days from opening. It is tied to maleness.

Arisaema fargesii breaks it the other way: in two cultivated specimens, some female spathes had a distinct basal exit as well. Two plants is two plants, and the page says so — but it is a reminder that the lethal female is a strong tendency and not a law of nature.

Arisaema flavum cannot form a door at all — or rather, two of its subspecies cannot. In ssp. flavum and ssp. abbreviatum the spathe is fused halfway from the start, sealing the chamber shut, and theirs is the smallest inflorescence in the genus, the chamber barely ten millimeters across, with an appendix reduced to a stub. They appear to be self-fertile and to pollinate themselves: an isolated ssp. abbreviatum, raised from a single introduced corm in a European garden, set fruit with no pollinator available. Ssp. tibeticum is not like them. Measurements of living plants in Tibet suggest that it changes sex as many other species in the genus do: small plants tend to carry a male spadix and large ones a bisexual one, where the other two are bisexual whenever they flower. Its spathe is broader than ssp. abbreviatum’s, though shorter than ssp. flavum’s. And it is diploid where the other two are tetraploid — which is why it may be the parent taxon the other two came from. Arisaema flavum is also the most widespread species in the genus, running from western China to Yemen and climbing to well over four thousand meters.

Selfing, which those two subspecies appear to manage, is not the only way an Arisaema has been reported to set seed without a second plant. Guy Gusman, co-author of The Genus Arisaema, wrote on the Aroid-L mailing list that fertile seed exceptionally forms on a purely female spadix without crossing, which he took to be apomixis, seed formed without fertilization. He noticed it only once in more than ten years of observation: on a very early-flowering form of Arisaema consanguineum, at a time when, he was sure, no other Arisaema was in flower in his garden.²² It rests on that one observation, and on his own reading of it.

The measurement has been made once, on Arisaema triphyllum in the broad sense, in a maple wood on Montreal Island over three weeks of May. Six plants — three male, three female — carried a probe pushed three millimeters into the appendix and a second probe in the leaf stalk as a non-heating control, logged every ten minutes against ambient air.

That last comparison is what settles it. An appendix that is no warmer than the petiole beside it is not generating heat; it is simply a piece of plant sitting in the same weather. And the experiment had already removed the obvious confound: every inflorescence was kept under cardboard for the whole three weeks so that sunlight could not warm it. The fractions of a degree that survived are the residue of a shaded plant equilibrating, not a furnace.

What the plant uses instead

The authors’ reading is that Arisaema never needed to pay for heat, because the sun does the job well enough. Warmed passively through the day, the appendix releases its scent; the gnats it wants are active in the same hours; and the whole system works without the mitochondrial machinery that costs Arum so much.

Why it matters

Heat, in aroids, is usually read as the engine of deception: warm the tissue, throw the scent, pull the insect in from a distance. This genus demonstrates that the engine is optional. The trap that catches more thoroughly than any other in the family — the only one whose females, in most species, never let their pollinators go — is powered by nothing but wax, geometry and a smell most humans cannot detect.

The technical word is paradioecious: a population that looks dioecious at any one moment, because each plant is carrying one sex, but in which individuals move between sexes over their lives. Some plants, Arisaema triphyllum among them, can also produce a mixed inflorescence carrying both.

One grower’s account adds a stage before male and female. George R. Stilwell, Jr., writing on the Aroid-L list, described Arisaema as starting out neuter (not yet flowering), turning male in its second season, and turning female in a couple of years if growing conditions are good. Poor conditions, he wrote, can send a plant back to male and, in the worst case, hold it dormant for a whole season, and inadequate moisture is probably the principal problem.²³ In a second message he gave the course in brief: neuter at birth, male in youth, female with maturity, and back to male when stressed.²⁴ He gave it as something well understood, not as measurements of his own, so the second-season timing is one grower’s generalization and not a schedule.

The experiment, from 1922

John Schaffner did not merely observe the correlation between size and sex — he broke it on purpose. He lifted plants, cut away most of their roots, and replanted them, so that a large plant faced the coming season with a crippled supply line.

That is a striking piece of work for 1922, and it still stands as the experimental core of the story. Most of what has followed — the size thresholds worked out in Japanese populations, the demographic studies in North American woods — has refined the relationship rather than replaced it. One survey does not fit. In May 2024 on Shikoku, among 114 flowering Arisaema serratum, neither height nor pseudostem diameter predicted sex, and light did: plants in brighter spots were more likely to be female. In the same survey size did predict sex in four other species (Arisaema ehimense, 56 plants; Arisaema tosaense, 86; Arisaema ringens, 30; Arisaema iyoanum, 19).²⁷ A study in Nagano Prefecture, as the survey’s authors cite it, had found larger Arisaema serratum more likely to be female, so the same species has given both results in different places.²⁷

What it does to the trap

Sex change is what makes the lethal female possible. Because, in most species studied, a plant is male while it is small and female only once it is large, a population always contains both, and every gnat that escapes a male inflorescence has somewhere to carry the pollen to. It also means the killing is not evenly distributed: the plants doing it are the big, established, well-fed ones, and a gnat's chance of dying rises with the quality of the flower it chose.

The objection is embarrassingly simple. Plants that genuinely mimic fungi advertise with a well-known class of eight-carbon volatiles — the compounds responsible for the smell of a mushroom, which human noses detect easily. Most Arisaema inflorescences smell of almost nothing to a human being. Whatever they are broadcasting, it is not the mushroom signal.

Not every grower finds them scentless, and not every nose agrees. A grower who signed herself Susan wrote on the Aroid-L list that her pink form of Arisaema candidissimum, which bloomed very early for her, smelled like cotton candy.²⁵ In a message signed the same way in 2007, the writer said her Arisaema candidissimum smelled like cotton candy to her but that her husband could not smell it at all.²⁶ That is one grower’s report, not a measurement.

The clue in the sex ratio

The something else announced itself in the catch. Two closely related species growing side by side in Japan, Arisaema angustatum and Arisaema peninsulae, each trap a different and almost completely separate set of fungus gnats. And in both, the trapped gnats were overwhelmingly male — fifty-seven of fifty-eight in one, all thirty-eight in the other. The obvious innocent explanation — that males simply emerge earlier in the season — is probably ruled out, on the authors’ own unpublished emergence counts cited inside the paper: the same gnat comes out of the surrounding mushrooms at roughly one male to one female while the plant is in flower. And when the researchers cut the appendix off, whole or in part, the visits that stopped were the principal pollinator’s and nobody else’s, in both species: whatever each plant is saying, it says it from the appendix, and it is addressed to one species of male gnat.

A brood-site mimic should catch females, because females are the ones hunting for somewhere to lay. A signal that pulls in males and almost nothing else looks like a sex pheromone. That is the hypothesis the field has been working under since: not brood-site deception but sexual deception — the strategy of the Ophrys orchids, arrived at independently in an aroid.

Which turns the sex of the catch into a test

The mushroom mimic is the control that passes it. Arisaema sikokianum traps both sexes, and it traps them out of a group with no business anywhere but a fungus: Mycodrosophila flies, which feed on nothing else, made up 66.7 per cent of its visitors, Mycodrosophila gratiosa alone 37.2 per cent. Both sexes go to a mushroom, because a mushroom is a meal and a nursery at once; only males go to a female. A male-only catch points to sexual deception; a mixed-sex catch of fungus-feeders points to mushroom mimicry. The two strategies can sit in one genus without contradicting each other, and the sex ratio is what tells them apart. What a male-only catch means on its own is the less settled half: the researchers who measured the male bias say plainly that it is insufficient to confirm sexual deception, and the 2025 observations below push at it again.

The mimicry also isolates. Arisaema japonicum, as Kakishima and colleagues named the plants (a 2025 study on Shikoku folds that name into Arisaema serratum), grows alongside Arisaema sikokianum and draws an almost entirely different catch — sciarids, gall midges and mycetophilids — with a single drosophilid individual between them, of a species that did not turn up in Arisaema sikokianum at all. Two species, two advertisements, and next to no overlap in who answers — the same near-total separation Arisaema angustatum and Arisaema peninsulae show, reached by a different route.

2025: two seasons on film

The trouble with all of this was that the behavior had never been systematically recorded. Visits are so rare in the wild that the pollinator lists were built almost entirely from counting corpses, and the few direct watches recorded how gnats arrive, fall in or climb out, not what a male does once he is drawn to the plant. Then a handful of potted Arisaema serratum in an Okayama experimental plot — five plants in 2022 and three in 2023 — turned out to be visited constantly, and were filmed for two seasons.

And a twist: they arrive in crowds

The observation that complicates the sexual-deception reading is social. Nearly half of all scored visits — 825 out of 1,760 — had more than one male on the inflorescence at once, and as many as six were recorded together. Gnats stayed longer when others were present, and a second gnat already in place shortened the wait for the next one to arrive.

That is not what a female-mimicking decoy produces; a fake female should be a prize one male monopolizes. It is what a lek looks like — males gathering, signaling, and drawing in more males. So the current proposal is that the flower may be copying an aggregation pheromone rather than a sex pheromone: not here is a mate, but here is where everyone is. The genital extension and wing-fanning would then be the gnats’ own signaling, dispersing their pheromone from a stage the plant built.

One thing they are not doing: learning

A lethal trap ought to select hard for avoidance, and visits do fall off late in the season. But the decline tracked the inflorescences visibly wilting, and it coincided with a neighboring plant coming into flower and drawing the crowd away. More tellingly, individual visits got longer as the season went on — the opposite of what a gnat learning to be careful would do. There is still no evidence that fungus gnats learn to avoid Arisaema.

2024: the trap is a nursery

Working on Arisaema thunbergii on Yakushima, a team collected spathes with the insect corpses still inside, then did something nobody had thought to do: they incubated the dead inflorescences and waited to see what came out.

And there was a stranger detail. Forty-four of those offspring came from five inflorescences that contained no adult corpses of their own species at all. Something had laid eggs in those spathes and then left. Since the inflorescences in question had been sealed to imitate a female, that is indirect evidence that some females lay and then climb out through the top.

2024 again: and in the sister species, nearly all of them do

Arisaema urashima was the obvious next test, because it lacks the abrupt swelling at the base of the appendix that stops gnats climbing. Here the escape was not an inference.

The methodological sting

This is the part with consequences beyond one genus. For a hundred years, the pollinators of Arisaema have been identified by collecting the bodies out of the spathe. It is a sensible method for a plant whose visitors are so seldom seen arriving. But it has a blind spot so obvious in hindsight that it is painful: a pollinator that escapes leaves no corpse, and therefore does not appear on the list. Sciophila yokoyamai was invisible for a century because it was good at getting out.

2025: and in China, a grimmer version

The habit is not confined to two Japanese species. Work published in 2025 reports fungus gnats breeding inside the traps of four Chinese species, named here under the broad Flora of China concept of each group — Arisaema erubescens, Arisaema lobatum, Arisaema bockii and Arisaema wattii — and adds a detail that closes the loop unpleasantly: the larvae feed on the corpses of the trapped adults.

If that holds, the female inflorescence is not merely a nursery that happens to kill. The killing is what stocks the larder. The dead pollinators become the food supply for the next generation of pollinators, and the plant gets its pollen moved either way.

Nearly seven thousand checks were made across 159 plants in a Montreal wood over three weeks, each inflorescence opened and searched several times a day. The yield averages out to well under one insect per flower per day across a flowering period that runs the better part of a month.

Those are the male and the female plants of a single season. The same workers carried the count on — the bisexual plants of that season added back in, then a second year and a second Montreal population — to 355 insects from 12,086 inflorescence surveys across 437 Arisaema triphyllum plants. The 133 sits inside that total rather than beside it, and the two cannot be added. The larger count also states the case more bluntly than any rate can: in the first wood, across 185 plants and a whole flowering cycle, 63 per cent of male, 72 per cent of female and 80 per cent of bisexual inflorescences were visited by nothing at all.

The reading offered is that the long flowering period evolved secondarily, as insurance: at high latitude, under weather that can shut down insect activity for days at a stretch, a flower that stays open for three weeks will eventually catch a warm afternoon. The stigmas seem to stay receptive for something like thirteen to sixteen days, though that was judged by eye from the way the stigma surface changed, not measured.

The timing that does hold

Two thirds of everything caught — 67 per cent — arrived during the days when pollen was actually being released, and traffic collapsed the day after it finished: 8.6 insects a day during pollen release, 3.4 a day afterwards. The first insects of the season appeared on the same day the plants first smelled of anything. Whatever the scent is doing, it is doing it on schedule.

The species that would not cooperate — until it did

In the botanical gardens of Berlin-Dahlem, during the fieldwork behind the foundational survey, one species failed completely. Arisaema serratum attracted nothing at all, produced no smell the observers could detect, and did so while Arisaema amurense flowering a few meters away filled with gnats overnight. The authors put it down to some physiological deficiency in those particular plants and moved on.

The two results are not necessarily in conflict, and the page does not claim the earlier observers were mistaken. Different continents, different plants, a quarter-century apart — and the 2025 team are careful to say that their own plants are unusually attractive, far more so than Arisaema serratum in the wild. What can be said is that nobody has run the experiment that would explain either extreme, and that a genus whose visits are this rare will look like it has no pollinators at all if you watch the wrong plant in the wrong year.

Why kill the pollinator?

Two explanations are on the table, and they are not mutually exclusive.

The first is straightforward: with no way out, the gnat spends longer scrambling around the stigmas, so more pollen ends up where it is wanted. Retention as a mechanism for thoroughness.

The second is less comfortable: a dead gnat cannot go on to pollinate a rival female. On this reading the killing is not about the plant’s own seed set at all, but about denying a competitor.

Is the wild seed set healthy or catastrophic?

In New York State, Arisaema triphyllum populations were found setting so little seed — 60 to 80 per cent of females with no seed at all in any given year, and an average of about seven seeds per female per year, against hand-pollinated plants producing more than ten times as much — that the researcher wondered aloud whether the whole pollination system might now be maladaptive: a machine that worked better in the evolutionary past than it does today. The counter-argument is that gnat numbers depend on how good the previous autumn’s mushroom crop was, so bad years are simply normal and good years make up for them. Both positions are defensible. Neither has been tested across enough seasons to settle it.

What the killing costs, over generations

The same question can be put demographically: what does a population do, across many years, when its flowers keep killing the insects that serve them? That has been modeled — a population model of this system, built on published field data rather than measured in any one wood — and two of its results are worth carrying. The first is that being too attractive is dangerous. Where the flower pulls male gnats in hard enough, plant and insect can go down together: the trap destroys the population it lives on, and follows it. The second is that what holds the plant in place is not pollination at all. In the model the populations that persist are the ones that bud off daughter cormlets and move from male to female quickly; take those away and the population fails however well the flowers perform. A plant that kills its pollinators keeps its place by clonal increase and turnover rather than by seed.

Two things temper it. The model assumes the flower is imitating a female insect, which is the reading Part VI’s 2025 evidence complicates. And it predicts an effect on the gnats that has not been weighed in the field: the authors point to the very low visit rates reported from wild populations, then say plainly that the quantitative evidence for it has not been established.

The list of things not yet measured

The scent of the species the deception hypotheses are about has hardly been analyzed. The sexual-deception and aggregation-pheromone hypotheses both stand or fall on floral chemistry. Detailed volatile data exist for the one mushroom mimic, Arisaema sikokianum (nine plants); the same study sampled Arisaema japonicum (eight plants) and seven more species at one to four plants each, Arisaema angustatum among them, but only to compare them with mushrooms. Beyond that the published record offers a general statement that Arisaema scents contain short-chain aldehydes and alcohols, not tied to particular species.

Nobody knows whether the pollinator produces the pheromone the plant is supposed to be copying. The insect side of the deception has simply not been studied.

Heat has been measured in one species. Six plants, one Quebec population, one May. The Himalayan species flowering near the snowline and the tropical Asian ones are untested.

The African species have no pollination study. Eight species survive on East African mountains — in Ethiopia, Uganda, Tanzania, the Ruwenzori — thousands of kilometers from the rest of the genus, and the nearest thing to a record of their pollination is a single photograph of Arisaema enneaphyllum in Ethiopia with a gnat, most probably a fungus gnat, imprisoned in the spathe, and a note that its male spathe has an exit hole. Most of the Himalayan species have little more than a list of what was found inside them.

Nobody knows how far the nursery habit reaches. It has been predicted for the species that lack the swollen appendix base, and it has now turned up in four Chinese species as well. Whether it is a rare exception or a widespread and simply unlooked-for feature of the genus is exactly the sort of question that was settled wrongly for a century because nearly everyone was counting corpses.

1. Vogel, S. & Martens, J. (2000). A survey of the function of the lethal kettle traps of Arisaema (Araceae), with records of pollinating fungus gnats from Nepal. Botanical Journal of the Linnean Society 133: 61–100. The foundation, and Parts I, II and III entire: the wax gliding surface and the clogged mycetophilid foot pads, the mechanical filter that lets ants and short-horned flies walk away, the basal exit recorded across two dozen species and six sections, the three exceptions (fargesii, flavum, tortuosum), the nectaries of Arisaema consanguineum, and the argument that an unswitchable wax wall is what forced the second door into existence. Also the comparisons to Arisarum, Pinellia and Zomicarpa. Grade: multi-season field collections across nine species in Nepal, plus direct observation and SEM on cultivated plants in European gardens; the pollination sequence itself is watched, not experimental. Note: the only surviving scan carries a heavy watermark that corrupts binomials and digits, so no number is taken from it that has not been read off the page images.
2. Barriault, I., Gibernau, M. & Barabé, D. (2009). Flowering period, thermogenesis, and pattern of visiting insects in Arisaema triphyllum (Araceae) in Quebec. Botany 87: 324–329. Part IV entire, and most of Part VIII: the only measurement of spadix temperature ever made in this genus, and the source of the negative result the page is built around. Also the twenty-day flowering period, the 133-insects-in-6,983-surveys visitation rate, the 67 per cent pollen-release peak, the gall midges, and the ozone-or-mushrooms scent. Grade: measured, instrumented, with the right control — appendix against petiole, not merely against air, and every inflorescence shaded to remove sunlight. n=6 plants for temperature, 159 for visitation.
3. Barriault, I., Barabé, D., Cloutier, L. & Gibernau, M. (2010). Pollination ecology and reproductive success in Jack-in-the-pulpit (Arisaema triphyllum) in Québec (Canada). Plant Biology 12(1): 161–171. The sister paper to the entry above, and the larger count that finishes Part VIII: 355 insects from 12,086 inflorescence surveys across 437 plants, two years and two Montreal populations, and the proportions that matter most — in the first wood, across 185 plants, 63 per cent of male, 72 per cent of female and 80 per cent of bisexual inflorescences receiving nothing at all across a whole flowering cycle. Also the breeding system, the pollen loads, the bagging experiment and the hand-pollinations, and the flies determined to genus where the earlier paper stopped at family. Grade: measured — 437 plants across three surveys, with experiments. Its first season is the same fieldwork as the entry above: the 133 insects in 6,983 surveys there are the male-and-female part of the 147 in 8,112 here, so the two totals can never be added. It carries no temperature and no scent data of its own, and the ten to twelve days it gives for the flowering period cannot be reconciled with the twenty measured in the 2009 paper, which is the figure this page uses.
4. Kakishima, S., Tuno, N., Hosaka, K., Okamoto, T., Ito, T. & Okuyama, Y. (2019). A specialized deceptive pollination system based on elaborate mushroom mimicry. bioRxiv 819136. The mushroom mimicry of Part VI, first-hand: the visitors of Arisaema sikokianum — Mycodrosophila at 66.7 per cent and Mycodrosophila gratiosa alone at 37.2 per cent, both sexes of a fly that feeds on nothing but fungi — the near-total separation from the visitors of the sympatric Arisaema japonicum, the eight-carbon and terpene chemistry that points at wood-decaying polypores rather than mushrooms in general, and an appendix removal that dropped visits to Arisaema sikokianum from about 1.5 to about 0.8 insects per male inflorescence per day without changing which flies arrived. Grade: measured — visitor assemblages across two sympatric species, a volatile analysis and an appendix-removal experiment — but a preprint, carrying bioRxiv’s own notice that it has not been certified by peer review. It is the source of the mixed-sex catch that Part VI uses to separate the genus’s two deceptions, and of the scent samples from Arisaema japonicum and seven more species that Parts VI and IX cite; that is as much weight as it is asked to carry here. Its compound identities are taken from the text; the percentages in its volatile table are not used.
5. Suetsugu, K., Sato, R., Kakishima, S., Okuyama, Y. & Sueyoshi, M. (2021). The sterile appendix of two sympatric Arisaema species lures each specific pollinator into deadly trap flowers. Ecology 102(2): e03242. The male-bias data of Part VI, first-hand: the principal pollinator of Arisaema angustatum (Cordyla murina) was 98.3 per cent male, and both principal pollinators of Arisaema peninsulae were 100 per cent male — against a roughly even sex ratio emerging from the mushrooms nearby, that last figure the authors’ own unpublished emergence data, cited inside the paper. Also the removal experiment showing that each species’ principal pollinator answers its appendix and nothing else’s, and the size arithmetic of the door: gnats about a millimeter wide against an exit of about two. Grade: measured — trapped assemblages plus a two-species appendix-removal experiment. The authors state plainly that these traits are insufficient to confirm sexual deception, and this page keeps their hedge.
6. Suetsugu, K. (2022). Arisaema: pollination by lethal attraction. Plants, People, Planet 4: 196–200. The review that reopened the question, and the backbone of Part VI: the case that mushroom mimicry cannot be general because most Arisaema scents are imperceptible to humans while genuine mimics broadcast detectable eight-carbon compounds; the sexual-deception alternative; and the Sarracenia convergence. Grade: review — it argues, it does not measure. The Arisaema sikokianum mimicry evidence, the male-bias counts and the exit-hole manipulation are all taken from the primary studies — see the entries above and below.
7. Suetsugu, K., Nishigaki, H., Fukushima, S., Ishitani, E., Kakishima, S. & Sueyoshi, M. (2022). Thread-like appendix on Arisaema urashima (Araceae) attracts fungus gnat pollinators. Ecology 103: e3782. The appendix manipulation carried through to seed. Cutting the thread off the appendix cut Mycetophila visits significantly while leaving other visitors alone, and dropped fruit set from 79 to 42 per cent and seed set from 37 to 11 per cent. Grade: measured field experiment with three treatments and stated sample sizes — small n on the fruit-set arm (five and seven plants), and the page says so wherever it uses those figures.
8. Suetsugu, K., Nishigaki, H., Kakishima, S., Sueyoshi, M. & Sugiura, S. (2024). Back from the dead: a fungus gnat pollinator turns Arisaema lethal trap into nursery. Plants, People, Planet 6: 536–543. Half of Part VII: the 69 Leia ishitanii reared out of decaying Arisaema thunbergii inflorescences, the larvae eating spadix and mold without touching the ovules, and the 44 offspring from five spathes containing no adults of their own species. Grade: measured, three field seasons, 106 inflorescences incubated; the escape itself is inferred here, not watched — it is watched in the next entry.
9. Suetsugu, K., Nishigaki, H., Sato, R., Kakishima, S., Ishitani, E., Fukushima, S., Sugiura, S. & Sueyoshi, M. (2024). Fungus gnat pollination in Arisaema urashima: the interplay of lethal traps and mutualistic nurseries. Plant Biology 26: 1–8. The rest of Part VII, and the methodological warning the page ends on: Sciophila yokoyamai escaping female spathes under direct observation, 73 adults emerging from more than 22 inflorescences none of which held a conspecific corpse, and the authors’ own conclusion that a century of corpse-based sampling has been systematically blind to pollinators that survive. Grade: measured — 416 inflorescences incubated, plus a filmed cage experiment. The paper carries an internal inconsistency in the cage sample sizes, so this page prints no n for that experiment and reports only the qualitative outcome.
10. Nishigaki, H., Matsumoto, T. K., Miyazaki, Y., Hirobe, M., Kakishima, S., Okuyama, Y. & Suetsugu, K. (2025). Ethological evidence for sexually exploitative pollinator attraction by Arisaema serratum (Araceae). Journal of Plant Research. The newest work on the page and the whole back half of Part VI: 2,459 visits by male Cordyla sixi in 64 observation hours, the first ethogram in the genus — genital exposure, wing-fanning, zig-zag flight, and no ejaculation recorded in two years — the co-visitation data that point at an aggregation pheromone rather than a fake female, and the finding that the seasonal decline is senescence rather than learned avoidance. Grade: measured, two seasons, video-recorded, with mixed models; but eight plant-years in total, and the authors themselves caution that the morphology results rest on too few plants.
11. Kubo, T., Matsumoto, T. K., Miyazaki, Y. & Yano, O. (2024). Pollinators of Arisaema nambae (Araceae), endemic to Okayama and Hiroshima prefectures, western Japan. Journal of Asia-Pacific Biodiversity 17: 191–195. The independent check on the size filter in Part III: 113 insects from 24 spathes across three populations of an endangered endemic, with fungus gnat body widths measured against the roughly two-millimeter exit, and Arisaema pollen found on gnats taken from female spathes — direct evidence that they arrived from a male one. Grade: measured visitation with morphometrics and pollen loads.
12. Schaffner, J. H. (1922). Control of the sexual state in Arisaema triphyllum and Arisaema dracontium. American Journal of Botany 9(2): 72–78. Part V entire, and the oldest experiment on the page: root pruning drove female plants to male, and corms that recovered reverted to female in a later season — sex expression under resource control, reversible in both directions. Grade: manipulative experiment with controls, and it still stands. The only surviving scan is lossy and its figures cannot be read reliably, so this page reports the direction of every result and none of the counts. (The counts have since been read off the page images — of 25 female plants root-pruned, 21 went male — and the direction-only wording above stands by choice, not necessity.)
13. Barnes, E. (1935). Some observations on the genus Arisaema on the Nilgiri Hills, South India. Journal of the Bombay Natural History Society 37(3): 630–639. The first description of the one-way door, quoted in Part III: the overlapping spathe edges arching apart into a roundish orifice of one to two millimeters in male inflorescences, and its absence in females, with the outer edge thickened and pressing down instead. Grade: careful field description by a resident botanist; no experiment. Note on the date: the paper is usually filed as 1934, but the offprint carries no date on any page, and the number penciled on its opening sheet is a collection stamp, not a page number. Vogel & Martens (2000) and Kubo and colleagues (2024) independently cite it as 1935, volume 37, pages 630–639, which fits the paper’s own footnote describing a 1934 publication as already out. That is the citation used here.
14. Bierzychudek, P. (1982). The demography of jack-in-the-pulpit, a forest perennial that changes sex. Ecological Monographs 52(4): 335–351. The census behind Part V’s lifespan — “its long (15–25 yr) life is typical of most forest herbs” — and the hard numbers behind how rarely the wild cross happens: 60 to 80 per cent of females set no seed at all, an average of seven seeds per female per year, and hand-pollinated plants outproducing naturally pollinated ones of the same size by more than an order of magnitude. Also the finding that mortality falls sharply once a plant reaches flowering size and then differs neither between sexes nor among sizes. Grade: measured — three years, two populations, size-classified transition matrices. Her own methodological point is that the matrices varied too much between years to quote a single population growth rate, and none is quoted here.
15. Pettit, J. L. (2009). Pollinator deception and plant reproductive success in jack-in-the-pulpit. MSc thesis, Indiana State University, Terre Haute. The exit-hole experiment of Part IX, first-hand: a 1–2 mm hole cut into female spathes — against cotton-plugged cuts and unmanipulated plants — produced no detectable difference in fruit set. Grade: manipulative field experiment with the right controls and a small sample — the author says so, and fruit set was strongly bimodal — so it weakens the retention hypothesis without disproving it, which is exactly how Part IX uses it. Also in the thesis: 57 per cent of female plants set fruit, and thrips — found on under a third of plants — judged minor beside the fungus gnats.
16. Nakazawa, T., Matsumoto, T. K. & Katsuhara, K. R. (2024). When is lethal deceptive pollination maintained? A population dynamics approach. Annals of Botany 134: 665–682. The demographic argument in Part IX: a population model of the trap run forward in time — plants passing from juvenile to male to female and back again, both sexes throwing cormlets, insects breeding in mushrooms, decaying wood and litter, and pollination happening only when a male gnat that has already been inside a male plant enters a female one. It carries the co-extinction result, the finding that cormlets and a quick route to femaleness are what keep the plant in the system, and the two conservation results this page states: that removal for horticulture bites whichever sex is taken, and that loss of forest habitat came out weaker than the other disturbances modeled. Grade: theory — a mathematical model calibrated on published field data, not a measurement of any population. It assumes the plant is imitating a female insect, the hypothesis Part VI’s 2025 evidence complicates, and the authors say plainly that the quantitative evidence that a trap depresses its own gnat population has not been established.
17. Huang, W. & Yang, C.-F. (2025). Trapped fungus gnats oviposit in the lethal kettle of Arisaema while corpses provide essential food for larval development. Bulletin of the Ecological Society of America 106(3): e70028. The closing paragraph of Part VII — and the weakest citation on this page, deliberately flagged. This is a four-page photo gallery, not a research paper. It documents fungus gnats breeding in the traps of four Chinese species and larvae feeding on trapped adult carcasses, and that is all this page claims from it. Grade: photographic record only. The study it illustrates — Huang, Li, Wang, Yang & Ågren 2025, Scavenging contributes to larval food intake in fungus gnats using the Arisaema kettle trap as a brood site, Ecology — is not used here, and no figure from it appears.
18. Killian, C. (1929). Développement et biologie de l'Ambrosinia Bassii L. Bulletin de la Société d'Histoire Naturelle de l'Afrique du Nord 20: 257–278. (In French.) Cited for one clause only, in Part VIII: that Ambrosina bassii holds its inflorescence far longer than Arisaema triphyllum does. p. 260 — the inflorescence “se maintient fraîche pendant trois mois, se fane au cours du quatrième”, from a series dated 30 November to 10 March. Grade: single observation (n = 1), and Killian notes the timing is moisture-dependent — a month earlier on clay, and lifting an inflorescence off the ground advanced desiccation by weeks. An independent corroboration exists (Vignoli 1939 found inflorescences still freschissime two months after the spathe opened) but is not otherwise used on this page. Ambrosina does not keep “comparable hours” to Arisaema; it holds its inflorescence far longer.
19. Murata, J. (1990). Three subspecies of Arisaema flavum (Forssk.) Schott (Araceae). The Journal of Japanese Botany 65(3): 65–73. The protologue of ssp. tibeticum, and the source for Part III’s account of how the three subspecies differ. Spathe blade: ssp. tibeticum 1.5–4.0 × 1.5–2.5 cm, ssp. flavum 3.5–5.6 × 1.6–2.8 cm, ssp. abbreviatum 1.0–2.5 × 0.6–1.4 cm (pp. 71–72). Ssp. tibeticum is paradioecious, male or bisexual by size — 24 of 57 flowering specimens from one Tibetan collection were male — while the other two are always bisexual (pp. 67–68). Chromosomes 2n = 28 against 2n = 56, and the hypothesis that the tetraploids arose from the diploid (p. 68). Grade: herbarium measurement across the range, field observation of two Tibetan populations, and cultivated plants.
20. Kakishima, S. & Okuyama, Y. (2018). Pollinator assemblages of Arisaema heterocephalum subsp. majus (Araceae), a critically endangered species endemic to Tokunoshima Island, Central Ryukyus. Bulletin of the National Museum of Nature and Science, Series B 44(4): 173–179. The Tokunoshima visitor survey used in the Opening. Grade: measured trapped-visitor survey; pollinator status inferred. Sciaridae and Mycetophilidae dominated the catch, and the authors inferred that they were the major pollinators. They called it probably the first report for section Clavata.
21. Scholten, J., Sprenger, A., Hullihen, O. & Specht, C. D. (2025). A bookend in the Arisaema japonicum (Araceae) taxonomic debate: morphological and genetic evidence for synonymization. Phytotaxa 725(1): 1–10. The caveat in Part VI on the name Arisaema japonicum: 13 plants from five sites in Ehime Prefecture, Shikoku, were sequenced, the plants keyed as Arisaema japonicum were not set apart from those keyed as Arisaema serratum, and the authors place the name in synonymy under Arisaema serratum. Grade: a taxonomic ruling from one regional sample; it holds no pollination, scent or visitor data.
22. Aroid-L mailing list, Guy Gusman, August 29th, 2002 The apomixis report in Part III: a reply to a question about seed on a lone plant, in which the writer, co-author of The Genus Arisaema (2002), describes fertile seed on a purely female spadix without crossing, noticed once in more than ten years of observation, on a very early-flowering form of Arisaema consanguineum. Grade: a single first-hand observation by a specialist grower, with no germination or cytology test reported. Apomixis is his own reading, inferred from no other Arisaema being in flower in his garden at the time, and the page keeps it as that.
23. Aroid-L mailing list, George R. Stilwell, Jr., February 3rd, 1997 The neuter stage in Part V: a reply on how Arisaema changes sex, giving the course as neuter, then male in the second season, then female in a couple of years in good conditions, with poor conditions sending a plant back to male and, in the worst case, holding it dormant for a whole season, and inadequate moisture as probably the principal problem. Grade: a grower’s summary offered as general understanding, with a short reading list, not an observation or measurement of his own. The second-season timing is one grower’s generalization and is not used as a rule.
24. Aroid-L mailing list, George R. Stilwell, Jr., June 3rd, 1997 The same account in brief, in Part V: a reply about growing Arisaema sikokianum seedlings in Zone 5, describing Arisaema as neuter at birth, male in youth, female with maturity and back to male when stressed. Grade: the same writer restating the same account, so it adds a second message but not an independent report.
25. Aroid-L mailing list, Susan, July 12th, 2000 The cotton-candy scent in Part VI: a note, in a thread on how regularly Amorphophallus come into bloom, that a pink form of Arisaema candidissimum was the first aroid to sprout and bloom for the writer in each of two years and smelled like cotton candy. Grade: the impression of a grower who signs only a first name; subjective and unmeasured.
26. Aroid-L mailing list, Susan, June 23rd, 2007 The scent not everyone detects, in Part VI: a message in a thread on the smell of Amorphophallus bulbifer, saying that her Arisaema candidissimum smells like cotton candy to her, that her husband cannot smell it at all, and that some people simply cannot smell these aroids. Grade: again a first-name-only impression, subjective and unmeasured; signed the same way as the July 12th, 2000 message but not confirmed as the same writer.
27. Scholten, J. T. & Specht, C. D. (2026). Does size matter? The integrated roles of light, adaptive sex expression, and hybridization in a widespread Arisaema (Araceae) species from western Japan. Plant Ecology and Evolution 159(2): 197–207. The Shikoku survey in Part V: 305 flowering plants of five Arisaema species at five sites on north-western Shikoku in May 2024. In Arisaema serratum (114 plants) neither height nor pseudostem diameter predicted sex and light did; in Arisaema ehimense (56 plants), Arisaema tosaense (86), Arisaema ringens (30) and Arisaema iyoanum (19) both size measures predicted sex and light did not. The authors set the Arisaema serratum result against a Nagano study that found larger plants more likely to be female. Grade: measured — one cross-sectional survey in one season, with light read once at flowering and no prior-year, corm or age data, so it shows that light predicts sex in that sample and does not show that light causes the change.
28. Zeng, L., Shu, W.-J., He, H., Li, T., Yang, X.-C. & Li, L. (2023). Post-pollination barriers contribute to coexistence of partially pollinator-sharing Arisaema species (Araceae). Ecology and Evolution 13: e10696. The Hunan visitor census in Part IX: at Badagongshan National Nature Reserve in 2022, floral visitors aspirated from 60 Arisaema bockii, 64 Arisaema lobatum and 79 Arisaema erubescens (588, 315 and 697 arthropods), with fungus gnats the most frequent visitors of all three (49.84–88.09 per cent); and hand crossings of all three, with conspecific fruit set of 85.55–93.26 per cent (n = 514, 415 and 434 fruits for Arisaema erubescens, Arisaema lobatum and Arisaema bockii). Grade: measured — one reserve, one season; the census counts the visitors caught and does not show which of them carry pollen.