Herb. Cirsium arvense is an herbaceous perennial in the aster family . It occurs in nearly every upland herbaceous community within its range , and is a particular threat in grassland communities and riparian habitats . C. arvense is shade intolerant and can tolerate soils with up to 2% salt content . It grows on all but waterlogged, poorly aerated soils, including clay , clay loam, silt loam , sandy loam, sandy clay, sand dunes, gravel , limestone, and chalk , but not peat. It spreads primarily by vegetative means, and secondarily by seed. The seeds spread as a contaminant in agricultural seeds in hay and in cattle and horse droppings and on farm machinery. It produces an abundance of bristly-plumed seeds that are easily dispersed by the wind and they may also be transported by water. Nuzzo (1997) reports that American Indians purportedly used an infusion of C. arvense roots for mouth diseases. The Chippewa considered it to be a "tonic, diuretic, and astringent". Young shoots and roots "can be used in the same ways as asparagus," and were eaten in Russia and by Native Americans. The nectar of its flowers is also said to make good honey. Zouhar (2001) reports that the weed has been used by native people in the northeastern United States in remedies for worms and poison-ivy (Toxicodendron radicans) and was used to make a mouthwash for children, a treatment for tuberculosis, and a tonic for gastrointestinal ailments.
- Cirsium arvense is one of the most economically important agricultural weeds in the world. It was introduced to North America in the 1600s and soon was recognized as a problem weed. Weed control legislation against the species was passed by the Vermont legislature in 1795 (R. J. Moore 1975). Canada thistle is now listed as a noxious weed in most areas where it occurs. It has very high seed production , and the runner roots readily survive the fragmentation that accompanies cultivation. [source]
- Honeybees and bumblebees get a lot of bang for their buck on thistles. Being a composite flower, there are hundreds of tiny florets per plant, each one containing a nectar reward.
- Canada thistle was introduced to the United States, probably by accident, in the early 1600s and, by 1954, had been declared a noxious weed in forty three states. In Canada and the U.S., it is considered one of the most tenacious and economically important agricultural weeds, but only in recent years has it been recognized as a problem in natural areas.
Click on the language to view common names.
Common Names in English:
Californian Thistle, California Thistle, Canada Thistle, Canadian Thistle, Corn Thistle, Creeping Thistle, Field Thistle, Perennial Thistle
Common Names in French:
Chardon Des Champs, Chardon Du Canada, Cirse Des Champs
Common Names in Portuguese:
, biennials, or perennials
, 5-400 cm, spiny
. Stems (1-several) erect
, branched or simple
, sometimes narrowly spiny-winged. Leaves basal and cauline; finely bristly-dentate to coarsely dentate
or 1-3 times pinnately lobed
, teeth and lobes
green and glabrous
or densely gray-canescent, usually eglandular
. Heads discoid
, borne singly, terminal
and in distal axils, or in racemiform
, or corymbiform
arrays. ( Peduncles with ± reduced leaflike bracts.) Involucres cylindric
or spheric, (1-6 Ã—) 1-8 cm. Phyllaries many in 5-20 series, subequal
or weakly to strongly, outer and middle
and apices spreading
to erect, usually spine-tipped, innermost usually with erect, flat, often twisted, entire or dentate, usually spineless apices (distal portion of phyllary
in many species with elongate
, usually milky
in fresh material
but dark brown to black when dry) . Receptacles flat to convex
, epaleate, covered with tawny
to white bristles
. Florets 25-200+; corollas white to pink, red, yellow or purple, ± bilateral
long, slender, distally bent, throats
short, abruptly expanded. cylindric, lobes linear
bases sharply short-tailed, apical appendages
linear-oblong; style tips
elongate (as measured in descriptions
including the slightly swollen nodes, long cylindric fused portions of style branches and very short distinct portions) . Cypselae ovoid, ± compressed
, with apical rims, smooth
, not ribbed
, glabrous, basal attachment scars
; pappi persistent
or falling in rings
, in 3-5 series of many flattened, plumose
bristles or plumose, setiform scales (longer
bristles shorter than corollas except in C. foliosum and C.
arvense) . x = 17.
Species ca. 200: North America, Eurasia , n Africa.
Only three genera in Cynareae are represented by native species in the New World, and of these Cirsium is by far the most widely distributed and diverse . Native species of Cirsium range from sea level to alpine and from boreal regions of Canada to the tropics of Central America. Members of the genus occur in a myriad of habitats including swamps , meadows, forests , prairies, sand dunes, and deserts.
Preliminary molecular phylogenetic studies by D. G. Kelch and B . G. Baldwin (2003) indicated that this diversity is the product of a rapid evolutionary diversification based upon a single initial introduction from Eurasia. Relationships among the North American species are apparently complex , and molecular studies have only begun to provide an outline of phylogeny for these plants . Although there has been a remarkable evolutionary and morphologic diversification in North American Cirsium, it has not been accompanied by very much divergence in the base sequences of genes commonly used to elucidate phylogenetic relationships. This suggests either that the diversification has been very rapid or that genetic markers in North American Cirsium mutate more slowly than in most other lineages .
Chromosomal diversification has accompanied the morphologic radiation of North American Cirsium. Many New World Cirsium species share the chromosomal base number of x = 17 that also predominates in most Eurasian species. Among the North American thistles, however, is a mostly descending dysploid series with chromosome numbers ranging from n = 18 to n = 10. Very few instances of polyploidy are known among New World Cirsium.
Cirsium species of remarkably different morphologies often are able to hybridize . Although in some hybrid combinations fertility is reduced, in others the formation of complex hybrid swarms indicates a lack of breeding barriers and the potential for emergence of novel character combinations. In the absence of adequate sampling and field observations, hybrids may go unrecognized, treated as distinct taxa or as variants of non-hybrid taxa, or left occupying the indeterminate folders of herbaria. In other cases hybridization has been invoked without much evidence as an explanation for Cirsium variants encountered in herbaria or in the field. Hybrid combinations are listed herein when evidence is convincing. Additional hybrids are likely to be found where the ranges of Cirsium species overlap. I have seen no documentation of hybridization between native American Cirsium species and introduced Eurasian taxa.
Much of the geographic range currently occupied by New World Cirsium species was greatly affected by the events of the Quaternary . Large areas were glaciated and other areas were vastly different during glacial episodes. The ancestors of thistles that currently occupy the high mountains of western North America were undoubtedly displaced elevationally and/or latitudinally during the recurrent glacial and interglacial episodes of the Pleistocene . Taxa that are currently isolated may have been in contact during glacial episodes with the opportunity for hybridization and genetic interchange. Episodes of prehistoric hybridization may have led to some of the character combinations found in modern American thistles, particularly in the western half of the continent. Current isolation and localized selection or genetic drift apparently have promoted differentiation of populations separated on mountaintop islands.
One of the most challenging aspects for a taxonomist studying New World Cirsium is the presence of species complexes that are apparently evolutionary works in progress. Some of the thistles, especially in the mountainous western part of North America, are frustratingly polymorphic with much overlapping variability and intergradation of characters. Early taxonomists, basing their work on a limited sampling of the morphologic diversity, named many of the forms as species, and the literature is rife with species names . The infilling that results from more collectors visiting more localities within the ranges of these complexes has blurred the boundaries between many of the proposed species and often added forms that do not "fit" the characteristics of named species. As I faced the challenges of preparing this treatment, I recognized that maintaining some of the named entities as species would, for consistency, require a further proliferation of species names. I have chosen to go the other way. Instead of proposing yet more ill-defined microspecies, I have chosen to recognize that the groups in question are rapidly evolving, only partially differentiated assemblages of races that have not reached the level of stability that is usually associated with the concept of species. Certainly much of such variation within the genus deserves a level of taxonomic recognition, or at least should be mentioned, but for those assemblages I think it much more prudent to recognize varieties -- entities that may be expected to freely intergrade -- rather than species.
Many problems remain to be worked out in North American Cirsium. Further investigation will undoubtedly reveal the need for refinement or major revision within some of the species groups. Studies that focus on variation within and among populations and on the biological basis for the variations are much needed. The field is open and the challenges are many.
Preparation of a workable key to Cirsium species has been frustratingly difficult. Extensive and overlapping ranges of variation in morphologic characteristics often require that a species be keyed two or more times. The resulting key is longer and more complex than I would prefer, and I have no doubt ignored, overlooked, or been completely unaware of variants that will not key out. Caveat clavitor!
The reputation of Cirsium has suffered greatly as a result of the introduction to North America of a few invasive weedy species from Eurasia. Cirsium vulgare (bull thistle) and C. arvense (Canada thistle€”a misnomer) have long been despised as noxious weeds . In recent years C. palustre (European swamp thistle) has joined their ranks . Additionally, weedy Eurasian species of Carduus, Onopordum, Centaurea, etc. , add to the public perception that all thistles are bad. Most North American native Cirsium are not at all weedy, and many are strikingly attractive plants. All are spiny plants that command respect, but they deserve a better reputation as one of North America€™s evolutionary success stories.
Native Cirsium species have come under threat from biocontrol programs instituted to suppress populations of weedy introduced thistles. Beginning in 1968 the seedhead weevil Rhinocyllus conicus has been widely introduced in various areas of the United States and Canada, primarily to control weedy species of Carduus. S. M. Louda et al. (1997) reported that R. conicus has crossed over to several native species of Cirsium. They observed that the number of viable cypselae in infested heads was greatly reduced; e.g. , heads of C. canescens infested by R. conicus produced 14.1 percent of the number of viable cypselae as in uninfested heads. Not all taxa are impacted as much as C. canescens, particularly those with later flowering phenology (Louda 1998) . R. W. Pemberton (2000) reported that 22 Cirsium taxa in North America are known hosts of R. conicus. I suspect that the number is higher. During my field work I have observed that the heads of many Cirsium species are heavily parasitized, although I have not determined which of these are infested by R. conicus and which by native seedhead parasites. The long-term impacts of R. conicus and other biocontrol agents on native thistles, particularly rare taxa, remain to be determined.
Species Cirsium arvense
Canada thistle is an herbaceous perennial
stems 1½-4 feet
tall, prickly leaves and an extensive creeping
. Stems are
branched, often slightly hairy
, and ridged
. Leaves are lance-shaped,
and are borne singly
and alternately along the stem. Rose-purple, lavender, or sometimes
white flower heads
appear from June through October, generally, and
occur in rounded
, umbrella-shaped clusters
The small, dry, single-seeded fruits of Canada thistle, called achenes, are 1-1½ inches long and have a feathery structure attached to the seed base . Many native species of thistle occur in the U.S., some of which are rare. Because of the possibility of confusion with native species, Canada thistle should be accurately identified before any control is attempted.
Perennials, dioecious or nearly so, 30-120(-200) cm; colonial from deep-seated creeping roots producing adventitious buds. Stems 1-many, erect, glabrous to appressed gray-tomentose; branches 0-many, ascending . Leaves: blades oblong to elliptic , 3-30 × 1-6 cm, margins plane to revolute , entire and spinulose , dentate , or shallowly to deeply pinnatifid , lobes well separated, lance-oblong to triangular-ovate, spinulose to few-toothed or few-lobed near base, main spines 1-7 mm, abaxial faces glabrous to densely gray-tomentose, adaxial green, glabrous to thinly tomentose ; basal absent at flowering, petioles narrowly winged , bases tapered; principal larger cauline proximally winged-petiolate, distally sessile, well distributed, gradually reduced, not decurrent; distal cauline becoming bractlike, entire, toothed, or lobed, spinulose or not. Heads 1-many, borne singly or in corymbiform or paniculiform arrays at tips of main stem and branches. Peduncles 0.2-7 cm. Involucres ovoid in flower, ± campanulate in fruit, 1-2 × 1-2 cm, arachnoid tomentose, ± glabrate . Phyllaries in 6-8 series, strongly imbricate, (usually purple-tinged), ovate (outer) to linear (inner), abaxial faces with narrow glutinous ridge , outer and middle appressed, entire, apices ascending to spreading , spines 0-1 mm (fine) ; apices of inner phyllaries flat, ± flexuous , margins entire to minutely erose or ciliolate . Corollas purple (white or pink) ; staminate 12-18 mm, (remaining longer than pappus when head is fully mature ), tubes 8-11 mm, throats 1-1.5 mm, lobes 3-5 mm; pistillate 14-20 mm, (overtopped by pappi in fruit), tubes 10-15 mm, throats ca. 1 mm, lobes 2-3 mm; style tips 1-2 mm. Cypselae brown, 2-4 mm, apical collar not differentiated; pappi 13-32 mm, exceeding corollas. 2n = 34. Flowering summer (Jun-Oct). [source]
Numerous variants of Cirsium arvense have been named based upon such features as pubescence , extent of leaf division, and spininess. Although extreme variants can be strikingly different, they are connected by such a web of intermediates that there seems to be little value in according any of them formal taxonomic recognition. [source]
Flowers: Bloom Period: April, May, June, July, August. • Flower Color: cream, lavender, magenta, purple, tan, violet
Size: 24-36" tall.
, pastures, roadsides, forest
Nuzzo (1997) cites that C. arvense occurs in nearly every upland herbaceous community within its range , and is a particular threat in prairie communities and riparian habitats . Throughout its range it is common on roadsides, in oldfields, croplands, and pastures, in deep, well-aerated, mesic soils. In eastern North America, it occasionally occurs in relatively dry habitats, including sand dunes and sandy fields, as well as on the edges of wet habitat, including stream banks, lakeshores, cleared swamps , muskegs and ditches. It is shade intolerant . It grows on all but waterlogged, poorly aerated soils, including clay , clay loam, silt loam , sandy loam, sandy clay, sand dunes, gravel , limestone, and chalk , but not peat. Zouhar (2001) reports that it can tolerate soils with up to 2% salt content . It grows best between 0 - 32 °Celsius. It tolerates annual precipitation ranging from 305-1015 mm per year and grows best with 400-750 mm of precipitation per year.
Canada thistle grows in barrens , glades , meadows, prairies, fields, pastures, and waste places. It does best in disturbed upland areas but also invades wet areas with fluctuating water levels such as streambank sedge meadows and wet prairies.
Typically found at an altitude of 0 to 2,848 meters (0 to 9,344 feet).
- Nuzzo (1997) states that C. arvense threatens natural communities by directly competing with and displacing native vegetation, decreasing species diversity , and changing the structure and composition of some habitats . Species diversity in an "undisturbed" Colorado grassland was inversely proportional to the relative frequency of C. arvense. It presents an economic threat to farmers and ranchers. Infestations reduce crop yield through competition for water, nutrients and minerals, and through interference with harvest . In Canada, the major impact of C. arvense is in agricultural land, and in natural areas that have been disturbed or are undergoing restoration . In the United States, it is a host for bean aphid and stalk borer , insects that affect corn and tomatoes, and for sod-web worm, which damages corn. In Bulgaria, C. arvense is a host for the cucumber mosaic virus. In addition to reducing forage and pasture production , it may scratch grazing animals, resulting in small infections . Zouhar (2001) reports that it has been identified as a management problem in many national parks and on TNC (The Nature Conservancy) preserves in the upper Midwest, the Great Plains states, and the Pacific Northwest. Infestations of C. arvense may contribute to the elimination of endangered and/or endemic plant species, such as the Colorado butterfly plant in Wyoming.
- Natural communities that are threatened by Canada thistle include non-forested plant communities such as prairies, barrens , savannas , glades , sand dunes, fields and meadows that have been impacted by disturbance . As it establishes itself in an area, Canada thistle crowds out and replaces native plants, changes the structure and species composition of natural plant communities and reduces plant and animal diversity . This highly invasive thistle prevents the coexistence of other plant species through shading, competition for soil resources and possibly through the release of chemical toxins poisonous to other plants .
- Canada thistle is declared a "noxious weed " throughout the U.S. and has long been recognized as a major agricultural pest, costing tens of millions of dollars in direct crop losses annually and additional millions costs for control. Only recently have the harmful impacts of Canada thistle to native species and natural ecosystems received notable attention.
- Management of Canada thistle can be achieved through hand-cutting, mowing, controlled burning , and chemical means, depending on the level of infestation and the type of area being managed. Due to its perennial nature, entire plants must be killed in order to prevent regrowth from rootstock . Hand-cutting of individual plants or mowing of larger infestations should be conducted prior to seed set and must be repeated until the starch reserves in the roots are exhausted. Because early season burning of Canada thistle can stimulate its growth and flowering, controlled burns should be carried out late in the growing season for best effect.
- In natural areas where Canada thistle is interspersed with desirable native plants, targeted application of a systemic herbicide such as glyphosate (e.g. , Roundup® or Rodeo®), which carries plant toxins to the roots, may be effective. For extensive infestations in disturbed areas with little desirable vegetation, broad application of this type herbicide may be the most effective method. Repeated applications are usually necessary due to the long life of seeds stored in the soil.
Canada thistle produces
of bristly-plumed seeds which
are easily dispersed by the wind. Most of the seeds germinate
a year, but some may remain viable in the soil for up to twenty years
or more. Vegetative reproduction in Canada thistle is aided by a
capable of sending out lateral
as deep as 3
feet below ground
, and from which shoots
sprout up at frequent intervals.
It also readily regenerates from root fragments less than an inch
Nuzzo (1997) states that the weed spreads primarily by vegetative means (by its root), and secondarily by seed. The root system can be extensive, growing horizontally as much as 6 m in one season , and individual roots live up to two years. Most patches spread at the rate of 1-2 m/year. Under good growing conditions, female plants produce an average of 29 flowering shoots/square meter, each with an average of 41 heads/shoot and 59 seeds/head. A single plant produces an average of 1500 and up to 5300 seeds. Multiple plants produced 100-64,300 viable seeds/m2 in Australia and up to 30,200/m2 in Holland.
Germination may be affected by ecotype, temperature , day length , depth of seed burial, substrate stratification , and seed freshness. Seeds from "male" plants are smaller and percent germination is lower. Seeds germinate best in warm temperatures 20 - 40 degrees Celsius, with alternating light and dark periods. At lower temperatures germination is aided by high light intensity . Germination at higher temperatures can help ensure that maximum germination takes place during warmer periods of the year. Seeds are somewhat tolerant of heat, and some were still viable after 10 minutes at 102 degrees Celsius and 2 minutes at 262 degrees Celsius, although viability was decreased at these temperatures compared to unheated controls . The seeds germinate over a wide range of soil moisture.
Duration: Biennial, Perennial
Culture: Space 15-18" apart.
Soil: Minimum pH: 5.1 • Maximum pH: 9.0
Sunlight: Sun Exposure: Full Sun .
Moisture: Drought Tolerance: High
Temperature: Cold Hardiness: 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a. (map)
- Whittaker & Margulis,1978
- Haeckel, 1866
- Cavalier-Smith, 1981
- Sinnott, 1935 ex Cavalier-Smith, 1998
t communities of Beaverhead, Silver Bow, and
- Brongniart, 1843
- Takhtajan, 1967
- Takhtajan Ex Reveal, 1992
- Order: 8-19. () - Lindley, 1833
- Superorder: Campanulanae () - Takhtajan Ex Reveal, 1992
- Subclass: Asteridae () - Takhtajan, 1967
- Class: t communities of Beaverhead, Silver Bow, and () - Brongniart, 1843
- Subphylum: Euphyllophytina ()
- Phylum: Tracheophyta () - Sinnott, 1935 ex Cavalier-Smith, 1998
- Subkingdom: Viridaeplantae () - Cavalier-Smith, 1981
- Kingdom: Plantae () - Haeckel, 1866 - Plants
Breea arvensis (L.) Less. • Carduus arvensis (L.) Robson • Cephalonoplos arvense (L.) Fourr. • Cirsium arvense var. argenteum (Vest) Fiori • Cirsium arvense var. horridum Wimmer and Grab. • Cirsium arvense var. integrifolium Wimmer and Grab. • Cirsium arvense var. mite Wimmer and Grab. • Cirsium arvense var. vestitum Wimmer and Grab. • Cirsium incanum (Gmel.) Fisch. • Cirsium setosum (Willd.) Bess. Ex Bieb. • Cnicus arvensis (L.) Hoffm. • Serratula arvensis L.
Status: Accepted Name
Last scrutiny: 17-Nov-09
Members of the genus Cirsium
ZipcodeZoo has pages for 146 species, subspecies, varieties, forms, and cultivars in this genus. Here are just 100 of them:
C. altissimum (Roadside Thistle) · C. amblylepis (Mt. Tamalpais Thistle) · C. andersonii (Anderson's Thistle) · C. andrewsii (Franciscan Thistle) · C. araneans (Jeweled Thistle) · C. arcuum (Powderpuff Thistle) · C. aridum (Cedar Rim Thistle) · C. arizonicum (Arizona Thistle) · C. arizonicum var. arizonicum (Arizona Thistle) · C. arizonicum var. nidulum (Arizona Thistle) · C. arvense (Californian Thistle) · C. barnebyi (Barneby's Thistle) · C. brevifolium (Palouse Thistle) · C. brevistylum (Clustered Thistle) · C. calcareum (Cainville Thistle) · C. californicum var. californicum (California Thistle) · C. callilepis var. callilepis (Fringebract Thistle) · C. canalense (Canal Thistle) · C. canescens (Platte Thistle) · C. canovirens (Gray Green Thistle) · C. canum (Queen Anne's Thistle) · C. carolinianum (Carolina Thistle) · C. chellyense (Queen Thistle) · C. chuskaense (Monarch Thistle) · C. ciliolatum (Ashland Thistle) · C. clavatum (Fish Lake Thistle) · C. clokeyi (Charleston Mountain Thistle) · C. congdonii (Rosette Thistle) · C. crassicaule (Slough Thistle) · C. crassum (Thistle) · C. cymosum (Peregrine Thistle) · C. diacanthus (Ivory Thistle) · C. discolor (Field Thistle) · C. douglasii (Douglas Thistle) · C. douglasii var. breweri (Douglas' Thistle) · C. douglasii var. breweri (Petr.) Keil & C.Turner (Douglas' Thistle) · C. douglasii var. douglasii (Douglas' Thistle) · C. douglasii var. douglasii DC. (Douglas' Thistle) · C. drummondii (Drummond Thistle) · C. eatonii (Eaton Thistle) · C. eatonii var. eatonii (Eaton's Thistle) · C. edule (Edible Thistle) · C. engelmannii (Engelmann Thistle) · C. eriophorum (Woolly Thistle) · C. erosum (Glory Thistle) · C. flodmanii (Flodman Thistle) · C. foliosum (Drummond's Thistle) · C. fontinale (Fountain Thistle) · C. fontinale (Greene) Jeps. var. campylon (H.K.Sharsmith) Pilz ex Keil & C.Turner (Fountain Thistle) · C. fontinale var. campylon (Mt Hamilton Thistle) · C. fontinale var. fontinale (Fountain Thistle) · C. fontinale var. obispoense (Chorro Creek Bog Thistle) · C. gilense (Gila Thistle) · C. grahamii (Graham's Thistle) · C. griseum (Gray Thistle) · C. hallii (Hall's Thistle) · C. helenioides (Melancholy Thistle) · C. heterophyllum (Curly Head) · C. hillii (Hill's Thistle) · C. hookerianum (Hooker Thistle) · C. horridulum (Bristly Thistle) · C. horridulum Michx. var. vittatum (Small) R.W.Long (Yellow Thistle) · C. horridulum var. horridulum (Yellow Thistle) · C. horridulum var. vittatum (Yellow Thistle) · C. humboldtense (Humboldt County Thistle) · C. hydrophilum (Suisun Thistle) · C. hydrophilum var. hydrophilum (Suisun Thistle) · C. hydrophilum var. vaseyi (Vasey's Thistle) · C. inornatum (Cloudcroft Thistle) · C. iowense (Iowa Thistle) · C. japonicum (Japanese Thistle) · C. japonicum 'Pink Beauty' (Japanese Thistle) · C. kamtschaticum (Kamchatka Thistle) · C. laterifolium (Porcupine Thistle) · C. lecontei (Le Conte's Thistle) · C. loncholepis (La Graciosa Thistle) · C. longistylum (Long-Styled Thistle) · C. mendocinum (Mendocino Thistle) · C. mexicanum (Mexican Thistle) · C. modestum (Lacy Thistle) · C. mohavense (Mohave Thistle) · C. murdockii (Murdock's Thistle) · C. muticum (Swamp Thistle) · C. navajoense (Navajo Thistle) · C. neomexicanum (Lavender Thistle) · C. neomexicanum var. neomexicanum (New Mexico Thistle) · C. neomexicanum var. utahense (Utah Thistle) · C. nuttallii (Nutalls Thistle) · C. occidentale (Cobweb Thistle) · C. occidentale (Nutt.) Jeps. var. californicum (Gray) Keil and C.Turner (California Thistle) · C. occidentale var. californicum (Cobwebby Thistle) · C. occidentale var. compactum (Compact Cobwebby Thistle) · C. occidentale var. occidentale (Cobwebby Thistle) · C. occidentale var. venustum (Cobwebby Thistle) · C. ochrocentrum (Yellow-Spine Thistle) · C. olivescens (Summer Thistle) · C. oreophilum (Crow Thistle) · C. osterhoutii (Osterhout's Thistle) · C. ownbeyi (Ownbey's Thistle) · C. pallidum (Pale Thistle)
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Accessed through GBIF Data Portal November 18, 2007:
- Jyväskylä University Museum - The Section of Natural Sciences, Vascular plant collection of Jyvaskyla University Museum
- Marine Science Institute, UCSB, Paleobiology Database
- Missouri Botanical Garden, Missouri Botanical Garden
- Oregon State University, Vascular Plant Collection
- The Danish Biodiversity Information Facility, Botany registration database by Danish botanists
- The Swedish Museum of Natural History
- , Herbarium of Oskarshamn
- The Swedish Museum of Natural History
- , Lund Botanical Museum
- The Swedish Museum of Natural History
- , Plants
- UK National Biodiversity Network, Botanical Society of the British Isles - Vascular Plants Database
- UK National Biodiversity Network, Environment and Heritage Service - EHS Species Datasets
- UK National Biodiversity Network, Joint Nature Conservation Committee - Vegetation surveys of coastal shingle in Great Britain
- University of Alaska Museum of the North, University of Alaska Museum of the North Herbarium
- University of Washington Burke Museum, Vascular Plant Collection - University of Washington Herbarium
- Utah Valley State College
- , Utah Valley State College Herbarium
- Biodiversity Heritage Library NamebankID: 2657795
- Catalogue of Life Accepted Name Code: Ast-244
- Global Biodiversity Information Facility Taxonkey: 2494459
- Globally Unique Identifier: urn:lsid:ipni.org:names:78011-3
- GRIN Nomen Number: 100755
- Integrated Taxonomic Information System (ITIS) Taxonomic Serial Number (TSN): 36335
- Natural Heritage Network Species Identifier: PDAST2E090
- U.S.D.A. Plant Symbol: SEAR12
- Zipcode Zoo Species Identifier: 12785
- Plant Conservation Alliance's Alien Plant Working Group. Least Wanted http://www.nps.gov/plants/alien/fact/ciar1.htm [back]
- David J. Keil "Cirsium". in Flora of North America Vol. 19, 20 and 21 Page 57, 66, 82, 83, 93, 95, 96, 97, 100, 102, 1. Oxford University Press. Online at EFloras.org. [back]
- Mean = 91.180 meters (299.147 feet), Standard Deviation = 168.400 based on 20,000 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]