# Xanthium spinosum

Common-Names: Spiny Clotbur, Spanish Thistle, Dagger ,Cocklebur,
Daggerweed, Spiny Burweed, Thorny Burweed, Bathurst Burr

The following description of *Xanthium spinosum* is adapted from Abrams
(1940), Jepson (1951), Munz and Keck (1973), Robbins et al. (1970), and
Holm et al. (1977).

*Xanthium spinosum* is an erect, rigid, much-branched annual herb, 3-10
dm tall and up to 15 dm or more wide. Stems are striate, yellowish or
brownish gray, and finely pubescent. The cotyledons are
linear-lanceolate in shape, differing in appearance from later
developing leaves. True leaves are lanceolate, entire, toothed or lobed,
3-8 cm long, 6-26 mm wide, glabrous or strigose above, and
silvery-tomentulose beneath. They are dull gray-green above with a
conspicuous white midrib and short petioles (1 cm). Each leaf base is
armed at the axil with yellow three-pronged spines 2-5 cm long, often
opposite in pairs.

Flower heads are in axillary clusters or often solitary. Flowers are
inconspicuous, greenish, and monoecious; male flowers in almost globular
heads in axils of upper most leaves, and female flowers in axils of
lower leaves, developing into a bur. The bur is two-celled, oblong,
nearly egg-shaped, slightly flattened, 10-13 mm long, 4 mm wide, pale
yellowish, more or less striate, glandular, covered with slender,
hooked, glabrous spines from more or less thickened bases, with the two
apical beaks short and straight. Each bur contains two flattened,
thick-coated, dark brown or black seeds, the lower germinating first.

*Xanthium* is derived from the Greek word 'xanthos', meaning \"yellow\"
and is thought to refer to a yellow dye obtainable from some species
(Parsons 1973).

Unlike cocklebur (*X. strumarium*), spiny clotbur has conspicuous
narrower leaves tapering at both ends, short petioles, conspicuous
three-pronged spines at the leaf base, and egg-shaped burs covered with
hooked, thorny prickles.

*Xanthium spinosum*, a native of South America, has now spread to at
least 39 countries throughout the world, occurring between latitudes 43
degrees S and 50 degrees N. It is widely distributed in the
Mediterranean region and Europe, throughout most of Australia, in some
coastal African countries, and in southern parts of South America and
the United States. It is seldom found in the tropics (Holm et al. 1977).
In California, spiny clotbur is common at low elevations throughout the
state (Munz and Keck 1973). It was introduced to the state, probably by
way of Europe, sometime before 1870 (Robbins 1940).

*Xanthium spinosum* does not exhibit the morphological diversity of *X.
strumarium* and is considered the more genetically stable species (Love
and Dansereau 1959). It is a weed of open areas and waste places. The
plant grows along roads, in pastures, meadows, roadsides and disturbed
areas. It is sometimes common around waterholes and along floodplains,
canals, ditches, creek flats, river terraces, and other moist places.

*Xanthium spinosum* has not been as extensively studied as *X.
strumarium*, but the two species share many characteristics. In the
Northern Hemisphere, spiny clotbur flowers between July and September,
and fruits are produced from September to November. Most plants die in
early winter (Parsons 1973). They produce an average of 150 seeds per
plant.

The spiny bur has two elongated cavities, each containing one seed. The
lower seed has a shorter dormancy period and germinates first. Dormancy
of the upper seed has been found to be due to low

permeability of the seed coat to oxygen (Crocker 1906, Davis 1930).
Higher temperatures (32-38 C) or higher oxygen partial pressures can
overcome dormancy. Both upper and lower seeds germinate readily if the
seed coat is removed. The lower seed may germinate promptly or within a
few months after maturity, but the upper seed may not germinate for
several months or even years. This staggered germination means that the
seedlings may emerge at any time over a period of several years during
favorable growing conditions (Redosevich and Holt 1984).

Spiny clotbur has a high water requirement and does best on warm, moist
soils. The seeds tend to germinate during the summer rains or whenever
soil moisture is adequate. Sometimes seeds germinate out of season, and
the resulting plants produce fruits out of season.

*Xanthium spinosum* was probably spread around the world by clinging to
the hair or wool of animals, to clothing, or to feedsacks, muddy tools,
etc. The seeds are sometimes dispersed in impure seedstocks and in weedy
hay (Holm et al. 1977). The seeds float and can be spread by water.
Parsons (1973) relates an unusual method of seed dispersal for spiny
clotbur: \"Some years ago an enterprising advertiser used the fruit of
Bathurst burr as the bodies of imitation butterflies with paper wings
bearing an advertisement, the idea being that the butterfly would be
thrown by passers-by to carry his message far and wide. This not only
spread the message but effectively spread the weed.\" In Argentina,
*Xanthium spinosum* has reportedly been used as a medicinal plant (Holm
et al. 1977).

Spiny clotbur is one of the world\'s worst weeds (Holm et al. 1977). It
is a serious weed in many agricultural crops and in animal production.
Spiny clotbur seeds are easily spread, due to their ability to float and
to \"hitchhike\" on humans and animals. The plants can quickly become
dominant in an area due to prolific seed production and high germination
and survival rates. The presence of two seed types in each bur also
increases its survival chances.

The plant invades pastures and grazing lands, causing reduced forage
production. It is not palatable to stock and becomes entangled in the
wool of sheep and pets. *Xanthium* species are toxic to most domestic
animals, particularly swine and horses. The poisonous compound in *X.
strumarium* (and presumably in *X. spinosum*), carboxyatractyloside, is
present in seeds (Cole et al. 1980). When ingested at 0.3 percent of an
animal\'s body weight, the seed will cause toxicity; but this situation
rarely occurs because the spiny burs are not palatable to animals.

When seedlings are in the cotyledonary stage, they are palatable but
also have the highest toxicity. Poisoning generally results when these
leaves are eaten. This situation occurs most often at the edges of
ponds, lakes, floodplains, or other bodies of water where shallow
flooding followed by recession of the waterline occurs. Under such
conditions seeds germinate readily, constantly supplying new generations
of potentially poisonous seedlings as the water source dries out.
Animals are attracted to such areas because of their need for drinking
water. The problem is accentuated because *Xanthium* seeds have a
natural dormancy and can germinate over long periods of time. Ingestion
of cotyledons to 0.75 to 1.5 percent of the animal\'s body weight will
cause toxicity.

Toxicity decreases rapidly as true leaves are formed. Evidence of
poisoning appears in about 12 to 48 hours, the symptoms being nausea,
vomiting, lassitude, depression, weakened muscles, and prostration.
Sever poisoning may result in convulsions and spasmodic running
movements. Ruminants may not vomit, but death may occur within a few
hours or days. Fatty substances such as milk, lard, or linseed oil have
been recommended as antidotes (Kingsbury 1964). The toxic agent

in *Xanthium* may also be responsible for allelopathic effects (Cutler
1983).

With the right combination of control measures, it should be possible to
eliminate spiny clotbur from selected areas. Constant monitoring will be
necessary since it can quickly re-establish from seeds. In shaded areas,
drier sites, and where competition from other plants is strong,
cocklebur control will be easier. Conversely, where light, soils, and
water levels are appropriate, the weed will be much more difficult to
eliminate.

Monitoring is needed to determine the effectiveness of cocklebur control
measures. These will vary depending upon the degree of the problem on a
given preserve.

*Xanthium spinosum* has not been studied as thoroughly as *X.
strumarium*. Research is needed pertaining to control measures, e.g.,
effects of prescribed burning on the plants and seed germination, and on
biological control.

Control of *Xanthium spinosum* requires active management once it
becomes established in an area. Control measures should aim at
preventing seeding for at least three years (Parsons 1973).

Frequent cultivation of fields can control *Xanthium spinosum* (Holm et
al. 1977). Physical removal of the plants by hand pulling or hoeing is
effective if done prior to flowering. Since the dormant seed can remain
viable for several years, periodic inspection of the area will be
necessary, and grubbing may have to be carried out to deal with
subsequent germination. Hoed or pulled plants on which the burs are
already formed should be removed and burned as the seed can mature

even on cut stalks (Australia Dept. of Agriculture 1974). Mowing or
rotary slashing will give effective control, but here again it should be
carried out before burs are formed. There is a danger also that after
cutting some burs will be formed on the cut stems close to the ground
(Parsons 1973).

Prescribed burning is an effective means to destroy *Xanthium spinosum*
seeds, but prescribed fire has not often been used for this purpose.

A fair amount of research has been conducted on insects associated with
spiny clotbur. Most of the insect associates of *Xanthium* in California
are polyphagous species. Twenty-one species

have been found associated with spiny clotbur in southern California
(Hilgendorf and Goeden 1983). Eleven of these species are also major or
minor pests of cultivated plants. Seven species associated with spiny
clotbur are endophagous (Diptera) and apparently are host specific to
*Xanthium* (Hilgendorf and Goeden 1983). The fruit fly, E. bullans, like
its only known host plants (Robbins 1940), is apparently an accidental
introduction from South America.

Little is known about *Oedopa capito*, which is widely distributed in
North America (Cole 1969). *O. capito* may have followed *Xanthium* into
California or it may be an undescribed native species that transferred
from unknown composites other than ragweeds and Helianthus species.
Hilgendorf and Goeden (1983) suggest that *Oedopa* sp. is probably the
only insect species worthy of study as a potential biocontrol agent for
*Xanthium*.

Studies of insects associated with spiny clotbur have also been
conducted in Kansas (Kelly 1931) and Texas (Wilson 1960). Six species
were introduced to Australia in an unsuccessful attempt to control
*Xanthium* (Wapshere 1974). Insect associates of *Xanthium* have also
been studied in India (Wilson 1960) and Pakistan (Baloch et al. 1968).
Neither area provided useful biocontrol agents. Baloch and Ghani (1969)
suggest that using a combination of several insects species with
different feeding habits would improve the chance of suppressing
*Xanthium* populations.

The rust *Puccinia xanthii* Schw. is an obligate parasite of species of
*Xanthium* and *Ambrosia* and occurs throughout the United States,
southern Canada, parts of Europe, and India (Conners 1967, Hasan 1974,
Alcorn 1975, Jaghav and Somani 1978). It attacks all aerial parts of the
plant except the flowers. Infected plants mature more rapidly than
healthy plants and show decreased transpiration, dry weight, bur
production, and percent germination (Hasan 1974, Julien et al. 1979).
The spores overwinter on dead plant parts.

Fungal and bacterial pathogens have had some success in controlling
*Xanthium strumarium* in India (Deshpande 1982). *Orobanche ramosa* L.
(broom rape) is a parasitic plant found on a variety of cultivated and
weedy plants, including *Xanthium* (King 1966, Polunin 1966, Munz and
Keck 1973).

Weaver and Lechowicz (1983) list 14 species of fungi that infect
*Xanthium* in the U.S. and Canada. *Colletotrichum xanthii* has caused
death of *X. spinosum* in areas of summer rainfall in New South Wales,
Australia (Wilson 1960, Nikandrow et al. 1984). The disease is favored
by wet weather during summer and autumn. Seedling plants may be killed
before the four-leaf stage, and in older plants, lesions are formed on
stems which may be girdled. Seed production may be only 10 to 20 percent
of normal, and viability may be reduced. The disease

can be established artificially in the field and will then persist
naturally. The fungi zinnia mildew (*Erysiphe cichoracearum*) and
*Verticillium dahliae* are also reported to infest *Xanthium spinosum*
(Holm et al. 1977).

Because of its toxicity and unpalatability, grazing is not a useful
control method for *Xanthium spinosum*.

Spiny clotbur is susceptible to a wide variety of soil- and
foliar-applied herbicides commonly used for the control of broad-leaved
weeds (Weaver and Lechowicz 1983). Near streams or lakes, particular
caution should be taken when using herbicides. Dr. Jim McHenry (1985),
of the University of California, Davis, recommends the following
herbicides for cocklebur control on California\'s preserves:

2,4-D is a phenoxy-type herbicide used for broadleaf weed control (it
does not affect grasses) that acts as a selective hormone or growth
regulating type. The chemical is non-corrosive and is generally
considered non-harmful to wildlife. It persists in the soil for 1-4
weeks. For spiny clotbur control 2,4-D ester should be applied to the
plants at the 3-5 leaf stage of growth. It is more effective than the
amine form in penetrating the cuticular wax on the leaves. Application
should be at the rate of 1-1.5 lbs/100 gallons of water with 1 quart of
surfactant/100 gallons.

Banvel (dicamba) is a broad-spectrum herbicide used against perennial
broadleaf weeds. It is non-flammable and non-corrosive and has a low
order of toxicity to fish and wildlife. It persists in the soil for 8
weeks. It is usually mixed at 4 lb/gal. Dicamba is more selective than
2,4-D.

Herbicides can be applied uniformly over an area (for large
infestations) or by spot spraying only the individual plants. Dr.
McHenry recommends using a flat-fan nozzle (Spraying Systems Co. #8003
or 8004 nozzle tip) rather than the cone nozzles available on most
garden sprayers. Cone sprayers produce greater atomization of the
chemicals and increase the chance of drift into unwanted areas. Spraying
should be done on calm days with dry plants

(dew or rain will dilute the herbicide, reducing its effectiveness).
When spraying large areas, a horizontal boom (6-8 feet long) made from
aluminum tubing will improve herbicide coverage.

*Xanthium spinosum* is a common annual weed spread by water and by
contact with humans or animals. It is native to South America, but has
spread throughout the world. Spiny clotbur is a weed of open places,
particularly sites with warm, moist soils. It reproduces from seeds that
are viable for up to several years. Biological control measures are
currently being investigated and may prove effective in the future.
Simple mechanical removal prior to flowering is recommended for control.
If pulled following flowering, the plants should be burned. Monitoring
should be continued on the sites for several years.

CITED REFERENCES

Abrams, L. 1940. Illustrated flora of the Pacific States. Stanford
University Press, Stanford. 4 volumes.

Alcorn, J.L. 1975. A new disease of Noogoora burr. Queensland
Agricultural J. 101:162. Australia Dept. of Agriculture, Agronomy
Division. 1974. Bathurst Burr, *Xanthium* spinosum, declared noxious
need. Tasmanian J. Agric. 45:207-209.

Baloch, G.M. and M.A. Ghani. 1969. The present status of biological
control of *Xanthium* (Compositae). PANS 15:154-159.

Baloch, G.M., A.I. Mohyuddin, and M.A. Ghani. 1968. *Xanthium
strumarium* L.\--insects and other organisms with it in West Pakistan.
Commonwealth Institute Biological Control Technical Bulletin 10:103-111.

Cole, F.R. 1969. The Flies of western North America. University of
California Press, Berkeley.

Cole, R.J., B.P. Stuart, J.A. Lansden, and R.H. Cox. 1980. Isolation and
redefinition of the toxic agent from cocklebur (*Xanthium strumarium*).
J. Agric. Food Chemistry 28:1330-1332.

Conners, I.L. 1967. An annotated index of plant diseases in Canada.
Agric. Canada Res. Br. Publication 1251. Ottawa, Ontario. 381 pp.

Crocker, W. 1906. Pole of seed coat in delayed germination. Botanical
Gazette 42:265-291.

Cutler, H.G. 1983. Carboxyatractyloside: a compound from *Xanthium
strumarium* and Atractylis gummifera with plant growth inhibiting
properties. The probable \"Inhibitor A.\" J. Natural Products
46:609-613.

Davis, W.E. 1930. The development of dormancy in seed of cocklebur
(*Xanthium*). American Journal of Botany 17:77-87.

Deshpande, K. 1982. Biocontrol of *Parthenium hysterophorus* L. and
*Xanthium strumarium* L. through phytopathogens. P. 48 in Abstracts of
Papers, Annual Conference of Indian Society of Weed Science.

Hasan, S. 1974. Recent advances in the use of plant pathogens as
biocontrol agent of weeds. Pest Articles and News Summaries 20:437-443.

Hilgendorf, J.H. and R.D. Goeden. 1983. Phytophagous insect faunas of
spiny clotbur, *Xanthium spinosum*, and cocklebur, *Xanthium
strumarium*. Environmental Entomology 12:404-411.

Holm, L.G., D.L. Pluncknett, J.V. Pancho, and J.P. Herberger. 1977. The
world\'s worst weeds. University Press of Hawaii, Honolulu. 609 pp.

Jadhav, A.N. and R.B. Somani. 1978. *Puccinia xanthii*\--a report from
India. Indian Phytopathology 31:369-371.

Jepson, W.L. 1951. Manual of the flowering plants of California.
University of California Press, Berkeley. 1238 pp.

Julien, M.H., J.E. Boradbent, and N.C. Matthews. 1979. Effects of
*Puccinia xanthii* on *Xanthium strumarium* (Compositae). Entomophaga
24:29-34.

Kelly, S.G. 1931. The control of Noogoora and Bathurst burr by insects.
J. Counc. Sci. Ind. Res. (Australia) 4:161-172.

King, L.J. 1966. Weeds of the world, biology and control. Interscience
Publications, New York. 526 pp.

Kingsbury, J.M. 1964. Poisonous plants of the U.S. and Canada.
Prentice-Hall, Inc., Englewood Cliffs, NJ. 626 pp.

Love, D. and P. Dansereau. 1959. Biosystematic studies on *Xanthium*:
taxonomic appraisal and ecological status. Canadian J. Botany
37:173-208.

McHenry, J. 1985. University of California, Davis, CA. Personal
communication.

Munz, P.A. and D.D. Keck. 1973. A California flora and supplement.
University of California Press, Berkeley. 1905 pp.

Nikandrow, A., G.J. Weidemann, and B.A. Auld. 1984. Mycoherbicide
co-operative project. P. 129 in R.W. Madin (ed.), Proceedings of the 7th
Australian Weeds Conference. Vol. 1. Perth, Australia.

Parsons, W.T. 1973. Noxious weeds of Victoria. Inkata Press, Ltd.,
Melbourne, Australia. 300 pp.

Polunin, N. (ed.) 1966. Weeds of the world: biology and control.
Grampian Press, Inc., London. 526 pp.

Redosevich, S.R. and J.S. Holt. 1984. Weed ecology. John Wiley & Sons,
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Robbins, W.W. 1940. Alien plants growing without cultivation in
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Robbins, W.W., M.K. Bellue, and W.S. Ball. 1970. Weeds of California.
State of California, Dept. of Agriculture. 547 pp.

Wapshere, A.J. 1974. An ecological study of an attempt at biological
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Research 25:275-92.

Weaver, S.E. and M.J. Lechowicz. 1983. The biology of Canadian weeds.
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Wilson, F. 1960. A review of the biological control of insects and weeds
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OTHER (UNCITED) REFERENCES

Gaines, X.M. and D.G. Swan. 1972. Weeds of eastern Washington and
adjacent areas. Camp-Na-Bor-Lee Association, Davenport, Washington. 349
pp.

Hilgendorf, J.H. and R.D. Goeden. 1982. Phytophagous insects reported
worldwide from the noxious weeds spiny clotbur, *Xanthium spinosum*, and
cocklebur, *Xanthium* strumarium. Entomological Society of America
28:147-152.

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