Monocarpy

“Semelparity” and “Big-bang reproduction” redirect here. For crises that recur, see Business cycle.

Monocarpy is the habit of flowering and setting seed only once and then dying. A plant with this habit is monocarpic; one that flowers and fruits repeatedly is polycarpic. The corresponding terms of ecology, applied to animals as well, are semelparity and iteroparity.¹² Annuals and biennials are monocarpic, and so are perennials that live for years or decades before their only flowering, such as the century plant (Agave), the talipot palm and many bamboos.³⁴⁵⁶

A model published by Lamont Cole in 1954 implied, in the words of a later review, that “the world should be filled with annuals dying after reproduction”; since it is not, the conclusion became known as Cole’s paradox. Later theory resolved it by taking account of the different mortality of young and adults: where the young die far more often than adults, as they usually do, repeated reproduction is to be expected.⁷¹ Many monocarpic plants flower only once they have reached a threshold size, and store reserves for years beforehand; when they flower, the reserves are spent at once.⁸⁹⁵¹⁰

Some monocarpic bamboos flower in synchrony after intervals of decades, set vast quantities of seed and die, and the glut can feed an explosion of rats.⁶ In the Mizo Hills of north-eastern India the flowering of Melocanna baccifera, called mautam, was followed by a famine in 1959–60. A relief organisation of those years, the Mizo National Famine Front, became the Mizo National Front, which led an armed uprising in 1966 and signed a peace accord twenty years later.¹¹¹²

Giant hogweed is a monocarpic perennial: it grows as a rosette for several years and flowers once, usually at three to five years old and in one recorded case at twelve, then dies.⁸ Cutting its leaves does not kill it, but postpones its flowering and so prolongs its life; see hydra effect.¹³ Common hogweed, by contrast, can flower in several successive years.¹⁴

Terms

Monocarpic and polycarpic

The terms appear in the Théorie élémentaire de la botanique (1813) of Augustin Pyramus de Candolle, the father of Alphonse de Candolle. His monocarpiens could fruit only once and died after fruiting, as wheat does; his polycarpiens could fruit several times, either from a persistent stem, as in the pear (caulocarpiens), or from new stems sent up by the root, each fruiting once, as in the banana (rhizocarpiens).¹⁵ In the second edition, of 1819, he divided the monocarps into annuals, biennials and plants that flower only after many years and then die.³

Lindley adopted the terms in English in 1832 as monocarpous. His monocarpous plants were annuals, biennials, and plants that live many years before flowering but die straight afterwards, such as Agave americana; the last group, he remarked, had no English name.⁴ B. D. Jackson’s Glossary of Botanic Terms (1905) records perennial monocarp as Möbius’s term for such plants.¹⁶

Semelparity and iteroparity

Semelparity and iteroparity are often credited to Lamont Cole, who used them in 1954.⁷ According to Hughes, Cole was the first to sort life histories into these two classes: a semelparous organism is one that “dies upon producing seed”, while iteroparous organisms range from those with two or three litters in a lifetime to trees that produce thousands.¹ The Latin semel means “once”.¹⁷

Gadgil and Bossert (1970) called the two strategies of perennial organisms those of “repeated reproducers” and “big-bang reproducers”. Big-bang reproducers put no effort into reproduction for many ages and then make a single “suicidal” reproductive effort; their examples were the Pacific salmon and “the bamboo tree”.² Later reviews use the term in the same sense.⁷

Hapaxanthic and pleonanthic

Prantl’s Lehrbuch der Botanik, in the ninth edition of 1894, edited by Pax, calls annuals and biennials hapaxanthisch, or monokarp, because they flower only once, and perennial herbs and woody plants that flower and fruit periodically polykarpisch. Some perennial herbs behave hapaxanthically, among them Echium vulgare and the umbellifer Angelica sylvestris, and so does the palm Corypha.¹⁸ Jackson’s glossary derives hapaxanthic from the Greek hapax, “once”, and anthos, “flower”.¹⁶

Palm botanists apply the word to the shoot. Tomlinson and Moore (1968) set palms whose lateral inflorescences do not stop the stem from growing, called pleonanthic by Corner, against hapaxanthic palms, in which a reproductive axis replaces vegetative growth entirely. Only in single-stemmed palms, such as Corypha, does this end the life of the individual; in clustering palms, suckers replace the dead stems, and the individual is polycarpic.¹⁹

Plietesial and mast seeding

According to Janzen (1976), Bremekamp coined plantae plietesiae, or plietesials, for perennial monocarpic plants that flower in synchrony; Janzen thought the word unnecessary.⁶ It is still applied to species of Strobilanthes that flower at long intervals.²⁰ For bamboos Janzen preferred mast seeding, the synchronised production of seed at long intervals by a population, to the traditional gregarious flowering; mast-seeding bamboos and Strobilanthes, he noted, are usually monocarpic.⁶

Theory

Cole’s paradox

For an annual species, Cole concluded, the gain in the intrinsic rate of population growth from switching to a perennial habit would be, in his words as quoted by Gadgil and Bossert and by Hughes, “exactly equivalent to adding one individual to the average litter size”.²¹ Since a parent that sacrificed itself could surely produce more than one extra offspring, dying after reproduction should be widely favoured; yet perennial, iteroparous life is common.⁷¹

Gadgil and Bossert traced the paradox to Cole’s assumption that nothing dies in its first year of life. Juvenile mortality, they argued, is typically far higher than adult mortality; if roughly one daughter of an annual parent survives to the age of one, switching to a perennial habit is worth about as much as doubling the average litter.² Charnov and Schaffer (1973), as summarised by Varpe and Ejsmond and by Hughes, added separate juvenile and adult mortality to Cole’s model: semelparity should then evolve when juveniles and adults face the same risk of death, and since juvenile survival is usually much lower, iteroparity is to be expected.⁷¹

Size and timing

In monocarpic plants the timing of flowering seems more closely tied to size or stage of development than to age.⁸ In teasel (Dipsacus fullonum) a rosette formed a flowering stalk only after reaching a critical size, and its size predicted its fate better than its age did; the same held for four so-called biennials, among them Oenothera biennis and Daucus carota.²¹²² Size is not simply a measure of stored reserves: in a Japanese dune population of Oenothera erythrosepala, which completed its life as a winter annual when fertilised, only rosettes more than 9 cm across bolted, whatever their age or the reserves in their taproot.²³ The threshold also varies: in three populations of Cynoglossum officinale it was highest where rosettes survived and grew best.²⁴

The single reproduction

In Gadgil and Bossert’s model, reproductive effort at a given age brings a “profit”, in reproduction at that age, and a “cost”, in lower survival and smaller size at later ages. Selection adjusts the effort at each age to maximise fitness over the whole life, and the shapes of the two curves decide whether repeated or big-bang reproduction is best.²a ledger kept in offspring

For a monocarpic plant, the “decision” when to flower is a trade-off between flowering as early as possible and accumulating more resources for a larger seed set, at a greater risk of dying before it reproduces. The strategy depends, in the words of Pergl and colleagues, on the balance between the risk of death and “the profit from delayed reproduction”, and so on habitat and management.⁸²⁵

Monocarpy can also be favoured where fitness rises more than proportionally with size. In foxglove (Digitalis purpurea), a facultative biennial, seed number rose in proportion to plant size, and seed size and the percentage and speed of germination also rose with the size of the mother.²⁶ The same plant, mostly biennial or perennial and iteroparous, becomes semelparous when its resources in the first year are high (Sletvold, as cited by Hughes); Hughes argues that parity is better treated as a continuum than as a dichotomy.¹

Occurrence

Annuals, the extreme monocarps, make up only about 6 per cent of plant species, according to an assignment of life cycles to some 235,000 species, half as many as had been thought. They are favoured in hot, dry regions, and the authors predict more annuals in 69 per cent of the world’s ecoregions by 2060.²⁷

Long-lived woody monocarps are uncommon. Tomlinson and Soderholm (1975) knew of some palms, Agave, a few dicotyledons and a branched tree of New Caledonia, Cerberiopsis candelabrum; otherwise, they wrote, comparable reproductive strategies are found only in annual weeds.²⁸ In 1977 Foster described Tachigalia versicolor, a large, much-branched canopy tree of Panama, Costa Rica and Colombia, as “suicidal”: within a year of flowering its leaves drop, its fruit is released and it dies. Its reproduction is synchronised at intervals of several years, though not all large trees flower and die at once.²⁹ Its seedlings grew and survived better under dying parent trees than under other trees.³⁰

Examples

Century plants

The popular name of Agave americana, the century plant, comes from a belief, recorded in 1886, that it blooms only after a hundred years. That year a greenhouse plant at Auburn, New York, bought in 1837 when it was twelve years old, came into bloom at about sixty-one, with a stalk 27 feet (about 8.2 m) high and about 4,000 buds; the account called the shoot the plant’s “dying effort”.³¹

In Mexico, the same account reported, the century plant was made “a profitable investment” to its owners. Once the flowering stalk had reached its full growth it was cut down, and the sap that filled the hollow at its base was ladled out and fermented into “agave wine”, or pulque; a tapped plant could yield a quart of sap a day.³¹the owners harvest the savings

Agave deserti, of the north-western Sonoran Desert, flowers after about 50–55 years. Its rosettes must exceed about 1,000 g of dry mass to flower, unless they are joined by a rhizome to a large flowering rosette, in which case they flower early.⁹ During flowering the nonstructural carbohydrate in the leaves fell from 38 to 6 per cent of their dry mass, and stored reserves supplied 70 per cent of the carbon for the 1.53 kg inflorescence.⁹ Small rosettes that flowered early could finish their inflorescence only with carbon from a connected large rosette, whose share fell from 74 per cent for a connected rosette of 0–30 g dry mass to 35 per cent for one of 200–600 g.⁹financed by the parent An inflorescence can produce about 65,000 seeds, yet over 29 years at one field site only the seed of 1967 and 1982 germinated and went on to establish.³²

Queen of the Andes

Puya raimondii, a bromeliad of the high Andes of Peru and Bolivia, grows slowly for decades, according to a Peruvian government research institute, while it accumulates the nutrients and energy to build a rosette about three metres tall; then it flowers, and after fruiting it withers and dies.³³ Its age at flowering has been estimated variously: 40–100 years according to one genetic study, the end of a life cycle of 80–100 years or more according to another, 80–100 years to maturity according to the institute, and 80–150 years in the wild according to a botanical garden.^34353336 In cultivation it has flowered at 28 years, at Berkeley in 1986, and at 33, in San Francisco in 2006.³⁶

Whole-genome data from 200 plants in nine populations show populations that are highly divergent and inbred, with an exceptionally high genetic load. The species has declined continuously since a bottleneck in the Pleistocene, whereas the iteroparous P. macrura recovered from it; the authors call the queen of the Andes “genetically fragile and fragmented” and ask whether this is “a consequence of long generation time and semelparity”.³⁴

Talipot palm

Hodge called the inflorescence of the talipot palm, Corypha umbraculifera, “nature’s biggest bouquet”: a terminal flower cluster often 20–30 feet (about 6–9 m) high and as broad, bearing countless thousands of small flowers, larger than that of any other flowering plant.⁵ Flowering comes after 30–40 years of steady growth, in which starch for the single reproductive event is stored in the soft pith of the trunk; people extract it as edible sago, felling the tree to do so. The palm’s early life, Hodge wrote, is spent “in building up food reserves sufficient for this mighty blossoming splurge”. As the food moves from the trunk into the inflorescence, the leaves wither and collapse, and when the fruits have ripened, after about a year, the palm dies.⁵saved for decades, spent at once

At Peradeniya, in Ceylon, twenty talipots were planted in an avenue in 1881. Seven began to flower in June 1918, at 37 years of age, and eight more in June 1922, at 41; the fruit of these ripened towards the end of 1923, and by June 1924 they were dead.³⁷ Seifriz concluded that the timing was an inherited tendency rather than a response to drought. He also noted that people habitually cut the leaves of young talipots for umbrellas and other uses, so that a palm might take twenty years or more to form a stem.³⁷

A palm of another species, Corypha elata, flowered in Miami in June 1971 after 44 years of growth from seed. Its inflorescence carried in the order of 10 million flowers and ripened about a quarter of a million fruits, weighing 545–817 kg dry. The palm had put some 15–22 per cent of the dry matter it produced in its life into this one reproduction, where annual weeds typically put 14–35 per cent (Harper and Ogden, as cited by the authors); despite its size, the authors concluded, it functions essentially as an “annual weed”.²⁸ For C. umbraculifera, J. B. Fisher estimated 24 million flowers on one plant.³⁸

Bamboos

Nearly all bamboos, Janzen found, have one of two life histories. Some, mostly outside the tropics of India and Asia, flower and seed every year for many years; in the others, after growing for a period of 3 to 120 years fixed for each species, nearly all the plants of a species in an area flower, set large quantities of seed and die.⁶ Phyllostachys bambusoides seeded en masse in China in 919 and 1114, in Japan between 1716 and 1735 and again in 1844–1847, and in the late 1960s both in transplanted stocks in England, Alabama and Russia and in the parent stock in Japan: a cycle of about 120 years.⁶ Veller and colleagues, citing Kawamura, also give 120 years but date the earliest record to 999.³⁹ The timing is set by an internal calendar rather than by the weather, and transplanted plants flower with their parent populations even in quite different climates.⁶¹¹³⁹

Janzen’s explanation was that seeding in synchrony after long waits satiates the seed predators at the level of the whole population; for bamboos these are typically rats, birds and pigs.⁶³⁹ The quantities are large. In 1867 a surveyor working in a 6,000-square-mile patch of Melocanna in India reported that the pear-sized fruits fell so thickly that they broke his plane tables and theodolites, and a mast of two Madagascar bamboos was estimated at 50 kg of seed per hectare over 100,000 ha.⁶flooding the market

After a mast in Madagascar an estimated 40–60 million rats moved into 10,000 ha of crops, which they destroyed before starving to death; rats have litters of six to twelve and mature in two to three months. A Burmese source quoted by Janzen says that after bamboo seeding rats can become so numerous that sowing field crops becomes impossible, and that famine and epidemics follow.⁶

Neelakurinji

Neelakurinji, Strobilanthes kunthiana, an undershrub of the Western Ghats in southern India, flowers en masse every twelve years; according to the records cited by Bera and colleagues, mass flowerings have followed at twelve-year intervals since 1838, and the authors, who saw the bloom of 2018, expect the next in 2030.²⁰

Bamboo flowering in Mizoram

Mautam

The bamboo Melocanna baccifera is Mau to the Mizo and muli elsewhere in India; mautam is its masting and the mass death that follows, tam meaning death. Its forests cover more than 26,000 km² of north-eastern India and extend into Myanmar and Bangladesh.¹¹ The species lives about 48 years, according to Aplin and Lalsiamliana; other sources give cycles of 40–50, 45–50 or 30–50 years, and the dates given for past mautams differ: 1815, 1863, 1911 and 1959 in sources cited by Aplin and Lalsiamliana, but 1862, 1911, 1956 and 2007 in Nag’s list.^11404142

M. baccifera has the largest fruit of any bamboo or grass, up to 300 g.⁴¹ In 2007–08, according to measurements cited by Aplin and Lalsiamliana, the fruit that fell on quadrats of 25 m² amounted to 25.6–83.6 tonnes a hectare; where farmers kept cutting the regrowing culms, the rhizomes still flowered.¹¹ According to Aplin and Lalsiamliana, the glut of nutritious fruit in the dry season sets the black rat (Rattus rattus) and other forest rats breeding early, so that their numbers build up several months earlier than in other years, and the ripening rice is damaged mainly by very young rats; litters are no larger, but breeding goes on out of season.¹¹

The famine of 1959–60

Famine had followed flowering before: British forces entering the Lushai Hills in the early 1880s found one attributed to rats that had multiplied on bamboo seed, in which about 15,000 people may have died (according to sources cited by Aplin and Lalsiamliana and by Nag).¹¹⁴² According to the Mizo record-keeper Rokhuma, as cited by Aplin and Lalsiamliana, Melocanna flowered gregariously in the east in 1958 and generally in 1959, when the increase in rats was “beyond imagination”; the harvest of October 1959 would last only until February 1960.¹¹ A local Anti-Famine Campaign Organization had been preparing since 1951, but the government of Assam, openly sceptical of the prediction, did not support its measures.¹¹ In October 1958 the Mizo District Council asked the governor of Assam for 150,000 rupees for precautions; the Assam government refused, dismissing the prediction as “a tradition of the primitive people” (Nag, as cited by Das).¹² Relief began only when famine was widespread, late in 1959, and for many communities it came too little and too late.¹¹ The government spent about 8.96 million rupees on famine relief in 1959–60 and 1960–61.⁴³

The number of deaths was not accurately recorded. Local estimates put the excess deaths at around 10,000, about 5 per cent of a population of some 200,000, with high infant mortality and outbreaks of cholera (as cited by Aplin and Lalsiamliana); other sources give 10,000–15,000 deaths across north-eastern India in 1959.¹¹⁴¹⁴⁰ In the Assam Legislative Assembly on 5 March 1966 the chief minister, B. P. Chaliha, said that the government’s spending and hard work had saved the Mizo people from “complete disaster”.⁴⁴ Nag writes that people contrasted the relief given by the British with the indifference of the Indian state in 1958, and that the insurgency in Mizoram began only after that famine.⁴²

The Mizo National Front

The Mizo Cultural Society, first formed in 1955, was renamed the Mautam Front in March 1960 and soon afterwards the Mizo National Famine Front (MNFF), which proved effective at distributing relief and at drawing attention to the plight of the Mizo.¹¹ Its young cadres collected donations from house to house and helped the district administration with relief.¹² The dates differ: the gazetteer has the society founded in 1959, and the famine front is dated to 1959, 1959–60, 1960 or, under the name MNFF, September 1960. Its founders are described variously as the Cultural Society, “some former Mizo soldiers” and a section of the Mizo Union.^434412454647

In October 1961 the MNFF became the Mizo National Front (MNF), whose declared aim was independence for a Greater Mizoram.¹¹ Das dates the change to 22 October, when the front dropped the word “famine” from its name; the gazetteer, to the night of 28 October, at the residence of Laldenga, a former soldier of the Indian army, who became its chairman.¹²⁴³⁴⁶the front outlived the famine On the night of 28 February 1966 large-scale violence broke out in many centres, among them Aizawl and Lunglei, in what was code-named Operation Jericho; on 1 March it became known that the MNF had declared independence, in a declaration signed by Laldenga and sixty others.¹¹¹²⁴⁶

The insurgency lasted twenty years.¹¹ The Mizo Hills became a Union Territory in 1972, on 22 January according to Das and on 21 January according to the gazetteer.¹²⁴³ A peace accord was signed in June 1986, on 25 June according to Das; Chandhoke dates it to 1985.⁴⁶¹²⁴⁷ Under it the MNF renounced violence and secession, and Laldenga became chief minister.⁴⁸ Mizoram became the 23rd state of the Indian Union on 20 February 1987, although one account dates statehood to 1986.¹¹⁴⁷⁴⁸ Chandhoke calls it the only case in India in which an insurgency ended with a peace accord; Aplin and Lalsiamliana remark that armed conflict has rarely ended so favourably for the insurgents, and that no other political movement can “trace its origin to an infestation of rats”.⁴⁷¹¹

The mautam of 2006–08

The most recent mautam is dated 2006–08, 2005–09, 2004–08 or 2004–09; gregarious flowering began in Mamit District in January 2005 and spread through Mizoram in 2007 and into 2008.¹¹⁴¹⁴⁰ Jhum rice production across the state fell to just over 10,000 tonnes, against more than 60,000 in each of the five preceding years, and almost no maize was harvested; in 2007, 1,400,000 rat tails were handed in, at 2 rupees each.¹¹ This time, thanks largely to a much improved road network, food relief usually reached those in need, and most people came through relatively unscathed. Farmers who had grown cash crops such as turmeric in place of jhum rice, however, found no market for them.¹¹the market did not come Mizo people link tlawmngaihna, a social obligation to be hospitable, unselfish and helpful, to Tampui Mitthi, the Great Famine, which stands for the recurrent hardships of bamboo flowering.¹¹

In giant hogweed

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A rosette for years

Giant hogweed (Heracleum mantegazzianum) lives as a vegetative rosette for several years, flowers once and dies; it does not reproduce vegetatively and relies entirely on seed.⁴⁹⁸ Pergl and colleagues aged plants by counting the annual rings in their roots. All 302 flowering plants they aged were at least three years old, and the median age at flowering was three years on unmanaged sites in the Czech Republic, where the plant is invasive, four on unmanaged sites in its native range in the western Greater Caucasus, and five on pastures in both.⁸ Flowering in the second year was seen only in a watered experimental garden, in 22 of 70 plants raised from seed (unpublished data cited by Pergl and colleagues), and never in the field.⁸²⁵

The oldest flowering plant found was twelve years old. It grew at an extremely dry, unmanaged Czech site that was left out of the statistics as an outlier, since most of its plants flowered between their fifth and eighth year.⁸ Under unfavourable conditions, on poor, shaded or dry sites or under regular grazing, the Best Practice Manual says, plants “can live for at least 12 years”; a later chapter says that they can postpone flowering “up to 12 years”.⁴⁹⁵⁰

Size, stress and cutting

See also: Hydra effect and Control of giant hogweed § Mowing and strimming

The reproductive output of a plant, scored on a scale corresponding to about 10,000–25,000 seeds, was unrelated to its age, which the authors read as a “threshold in the amount of resources” needed to trigger flowering.⁸ Studies in Germany and the Czech Republic, cited by Pergl and colleagues, suggest that the trigger is the plant’s size in the previous year, and that 90–100 per cent of the plants that reach the minimum size flower.⁵⁰ On pastures most plants flowered around their fifth year, probably because grazing and trampling injure them and they need more time to accumulate resources; the Best Practice Manual counts the ability to postpone flowering under stress, until enough reserves are stored, among the traits that make the species a successful invader.⁸⁴⁹

Cutting has the same effect. Cutting rosettes above ground, Pyšek and colleagues write, “will not kill plants, but extends their life span by postponing the time of flowering”; vegetative plants can be killed only by cutting the root.¹³postponed, not cancelled The manual explains repeated cutting and grazing as working by depleting the reserves of nutrients and energy stored in the root.⁴⁹

One flowering

Once flowering has begun, the plant dies. In 2004 twenty plants in a garden at Průhonice were cut at ground level, ten soon after the flowering stem appeared and ten when the terminal bud opened, and all regrowth was removed for the rest of the season; none survived to the following year.¹³ In the field the roots of flowering plants always died in mid-summer. Earlier reports of plants that survived flowering are thought to be misreadings of clumped plants: a young plant beside last year’s dead stem is easily taken for a resprouting rootstock.⁸²⁵ Among the myths overturned by the Giant Alien project were that the plant is biennial, which in the field it almost never is, and that it is polycarpic.¹⁰

Because the plant can store resources for years, they are “suddenly available for rapid utilization” when it flowers, to build a large, productive flowering structure; none of its herbivores or pathogens, at the densities observed, affects this flowering significantly, so that the plant in effect escapes them.¹⁰ An average plant at Slavkovský les produced 20,671 fruits, 44.6 per cent of them from the single terminal umbel.⁵¹ The strategy has a cost. Of 521 historical localities in the Czech Republic, the species persisted at only 124, or 23.8 per cent, against more than 70 per cent for clonal invaders under similar control; the authors link this partly to its reproduction, as a short-lived monocarp that depends on seed and a short-term seed bank, and so on disturbance.⁵²

Other hogweeds

Sosnowsky’s hogweed is also monocarpic, but Persian hogweed is a polycarpic perennial, which in northern Norway flowers year after year from the same root.⁵³⁵⁴ Most hybrids between giant and common hogweed did not die after flowering.²⁵¹⁴ Common hogweed, which Flora Europaea described as a biennial or short-lived perennial, did not usually behave as a biennial in Stewart and Grace’s garden: more than half of its plants survived five years, and many flowered in each of the four seasons observed.¹⁴

See also

• Giant hogweed § Life cycle
• Hydra effect
• Seed bank
• Umbel
• Apiaceae § Silphium
• Lag phase