Hieracium

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Hieracium
Yellow Hawkweed.jpg
Hieracium caespitosum
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Cichorieae
Genus: Hieracium[1]
L.
Synonyms
  • Chlorocrepis[2]
  • Crepidopsis Arv.-Touv.
  • Pilosella Vaill.[3]

Hieracium /h.ərˈæsiəm/,[4] known by the common name hawkweed[1] and classically as hierakion (from ancient Greek hierax 'hawk'),[5] is a genus of the sunflower (Helianthus) family Asteraceae (or Compositae), and closely related to dandelion (Taraxacum), chicory (Cichorium), prickly lettuce (Lactuca) and sow thistle (Sonchus),[6] which are part of the tribe Cichorieae. Hawkweeds, with their 10,000+ recorded species and subspecies,[7] do their part to make Asteraceae the second largest family of flowers.[8] Some botanists group all these species or subspecies into approximately 800 accepted species,[9] while others prefer to accept several thousand species. Since most hawkweeds reproduce exclusively asexually by means of seeds that are genetically identical to their mother plant (apomixis or agamospermy), clones or populations that consist of genetically identical plants are formed and some botanists (especially in UK, Scandinavia and Russia) prefer to accept these clones as good species (arguing that it is impossible to know how these clones are interrelated) whereas others (mainly in Central Europe and USA) try to group them into a few hundred more broadly defined species. What is here treated as the single genus Hieracium is now treated by most European experts as two different genera, Hieracium and Pilosella, with species such as Hieracium pilosella, Hieracium floribundum and Hieracium aurantiacum referred to the latter genus. Many members of the genus Pilosella reproduce both by stolons (runners like those of strawberries) and by seeds, whereas true Hieracium species reproduce only by seeds. In Pilosella, many individual plants are capable of forming both normal sexual and asexual (apomictic) seeds, whereas individual plants of Hieracium only produce one kind of seeds. Another difference is that all species of Pilosella have leaves with smooth (entire) margins whereas most species of Hieracium have distinctly dentate to deeply cut or divided leaves.

Description[edit]

Flowers and flower-heads[edit]

Hieracium or hawkweeds, like others in the Asteraceae family, have mostly yellow,[11] tightly packed flower-heads of numerous small flowers[8] but, unlike daisies and sunflowers in the same family, they have not two kinds of florets but only strap-shaped (spatulate) florets, each one of which is a complete flower in itself, not lacking stamens,[11] and joined to the stem by leafy bracts. As in other members of the tribe Cichorieae, each ray corolla is tipped by 3 to 5 teeth.[8]

Bracts, stems and leaves[edit]

Erect single, glabrous or hairy stems, sometimes branched away from the point of attachment, sometimes branched throughout.

The hairiness of hawkweeds can be very complex: from surfaces with scattered to crowded, tapered, whiplike, straight or curly, smooth to setae; "stellate-pubescent" or surfaces with scattered to crowded, dendritically branched (often called, but seldom truly, "stellate") hairs; and "stipitate-glandular" or surfaces with scattered to crowded gland-tipped hairs mostly. Surfaces of stems, leaves, peduncles, and phyllaries may be glabrous or may bear one, two, or all three of the types of hairs mentioned above.[12]

Like the other members of the Chicory tribe, hawkweeds contain a milky latex.[11]

Ecology[edit]

The Large Yellow Underwing (Noctua pronuba) feeds on Hieracium species.

Distribution[edit]

Hieracium species are native to Africa,[12]Asia, Europe, North America,[13] Central America and South America.

Species[edit]

The classification of Hieracium into species is notoriously difficult. One reason is the apomictic reproduction (in which plants asexually produce seeds), which tends to produce a lot of minor geographical variation. Over 9000 species names have been published in Hieracium but some botanists regard many of those as synonyms of larger species.[12]

Europe[edit]

North America[edit]

The list below is a selection of species that have been accepted by the USDA Natural Resources Conservation Service[1] and Canada.[14] A more complete list is given in the list of Hieracium species.

Plant pest[edit]

All species of the genus Hieracium are classed as invasive species throughout New Zealand. They are banned from sale, propagation and distribution under the National Pest Plant Accord. Hieracium is a pasture weed that reduces available feed for livestock and displaces the indigenous plants.[15] It is a particular threat in alpine ecosystems previously dominated by native tussocks, though it will colonise habitats from bare ground, to exotic pine forest, to native Southern Beech forest.[16]

In the United States, many species of Hieracium have been introduced and all species present are considered noxious weeds in one or more states.[17]

References[edit]

  1. ^ a b c Natural Resources Conservation Service (2007). "Classification for Kingdom Plantae Down to Genus Hieracium L.". The PLANTS Database. USDA, Baton Rouge, LA 70874-4490 USA. Retrieved 2007-12-18. 
  2. ^ International Organization for Plant Information (IOPI). "Vascular Plants of Russia and Adjacent Countries as of 26.10.96". Provisional Global Plant Checklist. International Organization for Plant Information (IOPI). Retrieved 2007-12-17. 
  3. ^ Germplasm Resources Information Network. "Genus: Hieracium L.". (GRIN) Online Database. USDA, ARS, National Genetic Resources Program. Retrieved 2007-12-23. 
  4. ^ "Guide to the Pronunciation of Specific, Generic and Family Names". Southern California Wildflowers. Retrieved 2007-12-22. 
  5. ^ Charters, Michael L. "HI-HY". California Plant Names: Latin and Greek Meanings and Derivations A Dictionary of Botanical Etymology. Retrieved 2007-12-26. 
  6. ^ Cooperative extension service, Matthew J. Rinella and Roger L. Sheley (December 2002). "Orange and Meadow Hawkweed, 199816". MontGuide fact sheet (Reprint ed.). Department of Land Resources and Environmental Sciences, Montana State University - Bozeman. Retrieved 2007-12-22. 
  7. ^ International Organization for Plant Information (IOPI). "Plant Name Search Results". International Plant Names Index. Retrieved 2007-12-17. 
  8. ^ a b c Peterson Field Guide, Theodore F. Niehaus (1976). Pacific States Wildflowers. The Peterson Field Guide Series. Illustrations by Charles L. Ripper. New York, New York 100003: Houghton Mifflin Company. pp. 102, 220. ISBN 0-395-91095-1. 
  9. ^ International Organization for Plant Information (IOPI). "Details for: Hieracium". Provisional Global Plant Checklist. Retrieved 2007-12-17. 
  10. ^ Edsall, Marion (2007-12-15) [1985]. Roadside Plants and Flowers A Traveler's Guide to the Midwest and Great Lakes Area. Cover design: Bruce Gore. 114 North Murray Street, Madison, Wisconsin 53715: University of Wisconsin Press. p. 46. ISBN 0-299-09704-8. Dewey 582.0977. "A dry roadside dotted with small, 3/4 inch red orange flowers, interspersed with very similar yellow ones, and often the white of daisies, is a good sign that you are in Hawkweed country." 
  11. ^ a b c Mrs M. Grieve (1933). "Hawkweed, Wood". A Modern Herbal. botanical.com. Retrieved 2007-12-16. 
  12. ^ a b c John L. Strother. "Hieracium in Flora of North America". FNA Vol. 19, 20 and 21. efloras.org. pp. Page 219, 278, 279. Retrieved 2007-12-16. 
  13. ^ Natural Resources Conservation Service (2007). "PLANTS Profile for Hieracium L.". The PLANTS Database. USDA, Baton Rouge, LA 70874-4490 USA. Retrieved 2007-12-18. 
  14. ^ Key to Indentification of Invasive and Native Hawkweeks (Hieracium spp.) in the Pacific Northwest, BC Ministry of Forests
  15. ^ "Hieracium species Detailed information sheet". The Weedbusters Management Committee (www.weedbusters.co.nz). Retrieved 2010-05-02. 
  16. ^ "Genetic diversity in tussock hawkweed (Hieracium lepidulum) and use of allele frequencies for identifying patterns of spread". 
  17. ^ "Hieracium L._hawkweed_USDA NRCS". 

Further reading[edit]

  • Espie, Peter (2001). Hieracium in New Zealand: ecology and management. Mosgiel: AgResearch. ISBN 0-478-20900-2. 
  • McCosh, D. and Rich, T.C.G. 209. Hieracium proximum (Caithness Hawkweed) in Ireland. Ir. Nat J. 30: 54.
  • Rich, T.C.G., Cotton, D.C.F., Hood, R.L.I.B., Houston, L., McCosh, J. and Jackson, M.B.W. 2009. Conservation of Ireland's biodiversity: status of the Irish endemic Hieracium basalticola Pugsley (Basalt Hawkweed) (Asteraceae). Ir. Nat J. 30: 79 - 89.

External links[edit]