Cirsium

Cirsium is a genus of perennial and biennial flowering plants in the Asteraceae, one of several genera known commonly as thistles. They are more precisely known as plume thistles. These differ from other thistle genera (Carduus, Silybum and Onopordum) in having feathered hairs to their achenes. The other genera have a pappus of simple unbranched hairs.[2]

Cirsium
Cirsium vulgare (spear thistle)
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Asterales
Family: Asteraceae
Subfamily: Carduoideae
Tribe: Cynareae
Subtribe: Carduinae
Genus: Cirsium
Mill.
Synonyms[1]
  • Cephalonoplos (Neck. ex DC.) Fourr.
  • Onotrophe Cass.
  • Lophiolepis (Cass.) Cass.
  • Eriolepis Cass.
  • Acarna Hill
  • Breea Less.
  • Cephalanophlos Fourr.
  • Erythrolaena Sweet
  • Cnicus L.
  • Cephalanoplos Neck.
  • Epitrachys (DC. ex Duby) K.Koch
  • Hemisteptia Bunge
  • Echenais Cass.
  • Orthocentron (Cass.) Cass.

They are mostly native to Eurasia and northern Africa, with about 60[3] species from North America (although several species have been introduced outside their native ranges).

Thistles are known for their effusive flower heads, usually purple, rose or pink, also yellow or white. The radially symmetrical disc flowers are at the end of the branches and are visited by many kinds of insects, featuring a generalised pollination syndrome.[4] They have erect stems and prickly leaves, with a characteristic enlarged base of the flower which is commonly spiny. The leaves are alternate, and some species can be slightly hairy. Extensions from the leaf base down the stem, called wings, can be lacking (Cirsium arvense), conspicuous (Cirsium vulgare), or inconspicuous. They can spread by seed, and also by rhizomes below the surface (Cirsium arvense). The seed has tufts of tiny hair, or pappus, which can carry them far by wind.

Cirsium thistles are used as food plants by the larvae of some Lepidoptera species - see list of Lepidoptera that feed on Cirsium. The seeds are attractive to small finches such as American goldfinch.

Most species are considered weeds, typically by agricultural interests. Cirsium vulgare (bull thistle, common thistle, or spear thistle) is listed as a noxious weed in nine US states.[5] Some species in particular are cultivated in gardens and wildflower plantings for their aesthetic value and/or to support pollinators such as butterflies. Some species dubbed weeds by various interest groups can also provide these benefits. Cirsium vulgare, for instance, ranked in the top 10 for nectar production in a UK plants survey conducted by the AgriLand project which is supported by the UK Insect Pollinators Initiative. Bull thistle was also a top producer of nectar sugar in another study in Britain, ranked third with a production per floral unit of (2323 ± 418μg).[6] Not only does it provide abundant nectar, it provides seeds and floss for birds, such as the American goldfinch, Spinus tristis, and supports the larvae of a Painted Lady butterfly, Vanessa cardui.[7] A great many native North American plants have weed in their common names, despite their beneficial qualities, such as Asclepias tuberosa, commonly known as butterflyweed. Some other common species are: Cirsium lanceolatum, Cirsium palustre, Cirsium oleraceum.

Some ecological organizations, such as the Xerces Society, have attempted to raise awareness of the benefits of thistles, to counteract the general agricultural and home garden labeling of thistles as unwanted weeds. The monarch butterfly, Danaus plexippus for instance, was highlighted as relying upon thistles such as Tall thistle, Cirsium altissimum, for its migration, as a very important nectar source.[8] Although such organizations focus on the benefits of native thistles, non-native thistles, such as Cirsium vulgare in North America, may provide similar benefits to wildlife. Some prairie and wildflower seed production companies supply bulk seed for native North American thistle species, for wildlife habitat restoration, although availability tends to be low. Thistles are particularly valued by bumblebees for their high nectar production.

Certain species of Cirsium, like Cirsium monspessulanum, Cirsium pyrenaicum and Cirsium vulgare, have been traditionally used as food in rural areas of southern Europe. Cirsium oleraceum is cultivated as a food source in Japan and India.

The word 'Cirsium' derives from the Greek word kirsos meaning 'swollen vein'. Thistles were used as a remedy against swollen veins. The flower blooms April to August.

Species
Hybrids
  • Cirsium × canalense – canal thistle
  • Cirsium × crassum – thistle
  • Cirsium × erosum – glory thistle
  • Cirsium × iowense – Iowa thistle
  • Cirsium × vancouverense – Vancouver thistle
  • Cirsium arizonicum (Arizona thistle)
  • Cirsium canum (Queen Anne's thistle)
  • Bumblebee on thistle a flowerhead (Cirsium arvense)
  • Cirsium vulgare (bull thistle, common thistle, or spear thistle)
  • Cirsium pyrenaicum cut and ready to cook
  • Texas purple thistle
  • Dried Cirsium in Canadian autumn

References
  1. Flann, C (ed) 2009+ Global Compositae Checklist Archived 2014-11-14 at Archive.today
  2. Rose, Francis (1981). The Wild Flower Key. Frederick Warne & Co. pp. 377–380. ISBN 0-7232-2419-6.
  3. "Cirsium". Flora of North America.
  4. Van Der Kooi, C. J.; Pen, I.; Staal, M.; Stavenga, D. G.; Elzenga, J. T. M. (2015). "Competition for pollinators and intra-communal spectral dissimilarity of flowers". Plant Biology. 18 (1): 56–62. doi:10.1111/plb.12328. PMID 25754608.
  5. "PLANTS Profile for Cirsium vulgare (bull thistle) USDA PLANTS". USDA Plant Database. USDA. Retrieved 2008-07-15.
  6. Hicks, DM; Ouvrard, P; Baldock, KCR (2016). "Food for Pollinators: Quantifying the Nectar and Pollen Resources of Urban Flower Meadows". PLOS ONE. 11 (6): e0158117. Bibcode:2016PLoSO..1158117H. doi:10.1371/journal.pone.0158117. PMC 4920406. PMID 27341588.
  7. "Which flowers are the best source of nectar?". Conservation Grade. 2014-10-15. Retrieved 2017-10-18.
  8. Eckberg, James; Lee-Mäder, Eric; Hopwood, Jennifer; Foltz Jordan, Sarah; Borders, Brianna (2017). "Native Thistles: A Conservation Practitioner's Guide". The Xerces Society. The Xerces Society. Retrieved 27 August 2018.
  9. English Names for Korean Native Plants (PDF). Pocheon: Korea National Arboretum. 2015. p. 412. ISBN 978-89-97450-98-5. Archived from the original (PDF) on 25 May 2017. Retrieved 22 December 2016 – via Korea Forest Service.

Further reading
  • Everitt, J.H.; Lonard, R.L.; Little, C.R. (2007). Weeds in South Texas and Northern Mexico. Lubbock: Texas Tech University Press. ISBN 0-89672-614-2
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