Common Names in English:
Bristly Thistle, Bull Thistle, Horrid Thistle, Purple Thistle, Spiny thistle, Yellow Thistle
The largest family of flowering plants , the Compositae (Asteraceae), comprising about 1,100 genera and more than 20,000 species and characterized by many small flowers arranged in a head looking like a single flower and subtended by an involucre of bracts. A head may consist of both ray flowers and disk flowers, as in the sunflower, of disk flowers only, as in the burdock, or of ray flowers only, as in the dandelion.
, 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 horridulum
Biennials or perennials, (± fleshy
cm; stout taproots
and a fascicle of fleshy lateral roots
by root sprouts. Stems 1-several, usually erect
often stout, glabrous
to densely tomentose
; branches 0-many, spreading
, short, stout. Leaves: blades
or oblong-elliptic, 10-40 × 2-10 cm, unlobed and spiny-dentate
to deeply pinnatifid
spiny-dentate or coarsely lobed
spines stout, 5-30 mm, abaxial
subglabrous to loosely tomentose,
glabrous to ± densely villous
basal present at flowering, spiny
principal cauline sessile, well distributed, often not much reduced
distally, bases often ± auriculate-clasping
; distal cauline
often spinier than the proximal
. Heads 1-20 in subcapitate
arrays (each closely subtended by an involucre-like
of spiny-margined bracts). Peduncles 0-5 cm. Involucres
, 3-5 × 3-8 cm. Phyllaries
in 5-9 series, subequal
to imbricate, light green to stramineous
lanceolate to linear, distally often with reddish margins
faces without glutinous
, often ± thinly tomentose, often
; outer and middle
bodies usually reddish-tinged, margins setulose-ciliolate, apices
acuminate, spines 1-2 mm, weak; apices of inner straight, flat. Corollas
white to yellow, pink, purple, or red, 30-47 mm, tubes
6-10 mm, lobes 7-10 mm; style tips
straw-colored to tan, 4-6 mm, apical collars
pappi 25-35 mm. 2n = 32, 33, 34, 35. [source]
Although several variants have been given taxonomic recognition as species, these seem at most races. Flower color varies greatly, sometimes within populations and sometimes on a populational or regional basis. Herbarium specimens are sometimes difficult to assign to variety. [source]
Flowers: Bloom Period: June, July, August, September. • Flower Color: cream, mauve , pale pink, pale yellow, purple, rose, tan
Size: 36-48" tall.
Typically found at an altitude of 0 to 2,500 meters (0 to 8,202 feet).
Duration: Annual , Biennial
Culture: Space 12-15" apart.
Soil: Minimum pH: 6.1 • Maximum pH: 7.8
Sunlight: Sun Exposure: Full Sun .
Moisture: Drought Tolerance: High
Temperature: Cold Hardiness: 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b. (map)
- Whittaker & Margulis,1978
- Haeckel, 1866
- Cavalier-Smith, 1981
- Sinnott, 1935 ex Cavalier-Smith, 1998
- Vascular Plants
- Brongniart, 1843
- Takhtajan, 1967
- Takhtajan Ex Reveal, 1992
- Order: Asterales () - Lindley, 1833
- Superorder: Campanulanae () - Takhtajan Ex Reveal, 1992
- Subclass: Asteridae () - Takhtajan, 1967
- Class: Spermatopsida () - Brongniart, 1843
- Subphylum: Euphyllophytina ()
- Phylum: Tracheophyta () - Sinnott, 1935 ex Cavalier-Smith, 1998 - Vascular Plants
- Subkingdom: Viridaeplantae () - Cavalier-Smith, 1981
- Kingdom: Plantae () - Haeckel, 1866 - Plants
Status: Accepted Name
Comment: Data Providers: CONABIO, Caribbean Checklist , New Zealand Plant Name Database, Govaerts World Compositae Checklist A-G, IPNI, Tropicos, LCR Editor. GCC LSID: urn :lsid:compositae.org:names:7A398CDE-453A-4A0C-A3BD-A53FFDE3995D
Last scrutiny: 21-Aug-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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- Ruggiero M., Gordon D., Bailly N., Kirk P., Nicolson D. (2011). The Catalogue of Life Taxonomic Classification, Edition 2, Part A. In: Species 2000 & ITIS Catalogue of Life: 2011 Annual Checklist (Bisby F.A., Roskov Y.R., Orrell T.M., Nicolson D., Paglinawan L.E., Bailly N., Kirk P.M., Bourgoin T., Baillargeon G., Ouvrard D., eds). DVD; Species 2000: Reading, UK.
- USDA, ARS, National Genetic Resources Program. Germplasm Resources Information Network - (GRIN) [Online Database]. National Germplasm Resources Laboratory, Beltsville, Maryland. URL (April 24, 2008)
Accessed through GBIF Data Portal November 24, 2007:
- Comisión nacional para el conocimiento y uso de la biodiversidad, Herbario del Instituto de Ecología, A.C., México
- Fairchild Tropical Botanic Garden, Fairchild Tropical Botanic Garden Virtual Herbarium Darwin Core format
- Missouri Botanical Garden, Missouri Botanical Garden
- USDA PLANTS, USDA PLANTS Database
- University of Alabama Biodiversity and Systematics, Herbarium
- Biodiversity Heritage Library NamebankID: 2657829
- Catalogue of Life Accepted Name Code: Ast-7113
- Global Biodiversity Information Facility Taxonkey: 2494459
- Globally Unique Identifier: urn:lsid:ipni.org:names:195474-1
- GRIN Nomen Number: 406927
- Integrated Taxonomic Information System (ITIS) Taxonomic Serial Number (TSN): 36379
- Natural Heritage Network Species Identifier: PDAST2E1E0
- U.S.D.A. Plant Symbol: CIHOV
- Zipcode Zoo Species Identifier: 13866
- 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 = 92.670 meters (304.035 feet), Standard Deviation = 200.090 based on 409 observations. Altitude information for each observation from British Oceanographic Data Centre. [back]