Glossary of hogweed terms

This glossary of hogweed terms defines the botanical, chemical, ecological and editorial terms used in Hogweed.org. Several of these words have acquired other meanings outside botany. In this encyclopedia they are used only in the senses given below.only

Botany

Andromonoecy

The bearing of male flowers and bisexual flowers on the same plant: from andro-, “male”, and monoecious, from Greek monos, “single”, and oikos, “house”, both kinds of flower living in one house. In giant hogweed the share of male flowers rises with the order of the umbel; see Umbel § Division of labour.

Apical dominance

The suppression of side buds by the growing tip (apex) of a shoot, mediated chiefly by the hormone auxin produced at the apex. Removing the apex (decapitation) releases the side buds, which then grow out. In hogweed, cutting off the terminal umbel commonly produces several smaller umbels in its place; see hydra effect.

Bolting

The rapid elongation of a flowering stem from a rosette. Giant hogweed bolts only once, in the final year of its life.

Capitate

Shaped like a head, or gathered into a dense head-like cluster. From Latin caput, “head”.

Crown

The junction of root and stem at or just below the soil surface, from which new shoots arise. Control is permanent only when the crown is destroyed or severed from the root.

Decapitation

In horticulture, removal of the apex of a shoot. It does not kill the plant; it redistributes growth to the side buds. See apical dominance.

Dormancy

A state in which a living seed does not germinate, even in favourable conditions, until a particular requirement — often a period of cold — has been met. See stratification.

Mericarp

One of the two halves into which the dry fruit of the carrot family (Apiaceae) splits when ripe. In hogweed each mericarp holds a single seed and is usually simply called a seed.

Monocarpic

Flowering and setting seed only once, then dying. Giant hogweed is a monocarpic perennial: it may live for several years as a rosette, but its first flowering is also its last.

Pollen donor

A flower, umbel or plant that contributes pollen but sets no seed of its own. In giant hogweed the umbels of the lowest order act only as pollen donors.

Protandry

The maturing of the male parts of a flower before the female parts, so that each flower sheds its pollen before it can receive any. In hogweed the whole umbel passes first through a male phase and then through a female one.

Radical

Arising from the root, or from the crown immediately above it. Radical leaves form the basal rosette. From Latin radix, “root”. In this encyclopedia the word is used only in this sense.

Rosette

A circular cluster of leaves at ground level. Giant hogweed spends most of its life as a rosette, accumulating reserves in the taproot for its single flowering.

Satellite umbel

A secondary umbel on one of the shoots that ring the terminal umbel. The satellites open after it and set less seed.

Self-compatible

Able to set seed with its own pollen. Giant hogweed is fully self-compatible, so a single plant can found a population.

Stratification

Exposure of seeds to a period of cold, moist conditions, which breaks their dormancy. In the wild it is supplied by winter; seed that has not been stratified does not germinate.

Taproot

A large, central root growing vertically downward, from which smaller roots branch. The hogweed taproot stores the reserves from which the plant regrows after cutting.

Terminal umbel

The umbel that ends the main stem: the first to open, the largest, and in giant hogweed the source of nearly half of the plant’s seed. See Umbel.

Umbel

An inflorescence in which the flower stalks (rays) spring from a single point, like the ribs of an umbrella (Latin umbella, “sunshade”). In a compound umbel each ray carries a smaller umbel of its own, the umbellet. See main article.

Umbellet

One of the small umbels borne at the end of each ray of a compound umbel.

Vitta

An oil duct in the fruit wall of the Apiaceae (plural vittae). In hogweed the vittae are conspicuous, dark and club-shaped, and help to identify the seed.

Chemistry

Angelicin

The parent compound of the angular furanocoumarins: the same three rings as psoralen, bent. It binds DNA once but cannot join two strands. Often the largest single furanocoumarin in hogweed.

Furanocoumarin

A class of plant compounds, including psoralen, bergapten and xanthotoxin, which are harmless in the dark but bind to DNA when activated by ultraviolet light. See main article and phytophotodermatitis.

Intercalation

The insertion of a flat molecule between the stacked base pairs of DNA. Furanocoumarins intercalate in the dark and react when light arrives.

Interstrand cross-link

A covalent bridge between the two strands of DNA, which prevents them from separating. A linear furanocoumarin that has formed a monoadduct can absorb a second photon and bind the opposite strand.

Monoadduct

A product in which a molecule has bound to one strand of DNA at one point. A furanocoumarin forms a monoadduct with a thymine after absorbing one photon of ultraviolet A.

Phototoxic

Harmful only in the presence of light. A phototoxic substance does nothing in the dark; see phytophotodermatitis.

Phytoalexin

A defensive compound that a plant makes in response to attack by a fungus or other microbe. Some furanocoumarins are phytoalexins.

Psoralen

The parent compound of the linear furanocoumarins, C₁₁H₆O₃: three rings in a straight row. Its methoxy derivatives are bergapten (5-MOP) and xanthotoxin (8-MOP, methoxsalen).

PUVA

Psoralen plus UVA: photochemotherapy with an oral or topical furanocoumarin followed by ultraviolet A, introduced for psoriasis in 1974. The same reaction that clears the skin can cause skin cancer.

Ultraviolet A

The longest-wavelength ultraviolet light, about 315 or 320 to 400 nm, which passes through the atmosphere in quantity. Hogweed burns are most efficiently caused at 330–335 nm.

Ecology

Catchment

The area of land drained by a river and its tributaries. Because hogweed seed travels downstream, the catchment, not the property, is the natural unit of control.

Colonisation

The establishment of a species in an area where it was not previously present.

Dominance

The degree to which one species controls the conditions of a community through its size, number or cover. A mature hogweed stand is dominated by a single species, which takes most of the light.

Enemy release

The escape of an introduced species from the herbivores and diseases of its native range. See Enemy release hypothesis.

Gini coefficient

A measure of inequality, from 0, when every member of a population has an equal share, to 1, when a single member has everything. Devised for incomes, it has been used since 1984 to describe hierarchies of size and output in plant populations. See Umbel § Inequality.

Hydra effect

An increase in the size of a population in response to an increase in the mortality of its members. See main article.

Hydrochory

Dispersal of seeds by water. Hogweed seeds float and are carried downstream along rivers, streams and ditches.

Invasion debt

The invasions that past introductions have already made certain but that have not yet happened. Across Europe, today’s alien species reflect the economy of 1900 better than that of 2000. See Lag phase.

Invasive species

A species introduced outside its native range whose spread causes harm to the environment, the economy or human health.

Lag phase

The period between the arrival of an invader and the start of its rapid spread. See main article.

Lorenz curve

A graph of the cumulative share of a total against the cumulative share of the population that holds it, ordered from the least to the most. The further the curve sags below the diagonal, the more unequal the distribution.

Monoculture

A community made up of a single species. Nothing else grows in it for long.

Pioneer species

The first species to colonise bare or disturbed ground, beginning the process of succession.

Propagule pressure

The number of individuals introduced to a place and the number of occasions on which they arrive. The more seed is moved, and the more often, the more likely an invasion.

Reproductive assurance

The ability to set seed without a mate, usually by self-pollination. It allows a single plant carried far from its kind to found a population.

Residence time

The time since a species was introduced to a region. The longer it has been present, the more widespread it tends to be.

Seed bank

The reserve of living seeds present in the soil. See main article.

Seed rain

The seeds arriving at a given area in a given period. The seed rain replenishes the seed bank.

Size class

A category into which the members of a population are grouped by size. The class structure of a stand shows whether it is growing, stable or declining.

Succession

The gradual, broadly predictable change in the species of a community over time, for example after disturbance or the removal of a dominant species.

Editorial terms

Citation needed

A tag placed on a claim that is not supported by a reliable source. Claims so tagged may be challenged and removed. Claims about the benefits of hogweed are tagged more often than any others.

Neutral point of view

The principle that articles represent significant views fairly and in proportion to their support in reliable sources. Neutrality between the plant and the people it burns is not required.

Red link

A link to an article that does not exist yet. A red link is not an error: it marks an article that has not yet been written.

See also

• Giant hogweed
• Control of giant hogweed