Hieracium

Orange hawkweed Hieracium aurantiacum, photographed by Orchi.

Belongs within: Cichorieae.

Hieracium, the hawkweeds, is a large cosmopolitan genus of composite-flowered herbs. Due to their often apomictic breeding system, recognition of species within Hieracium has been the subject of some controversy, with authors differing significantly in how many species should be recognised. A number of species of Hieracium are regarded as invasive weeds in pasture. Flowers are most commonly yellow; exceptions include the North American H. albiflorum with white flowers, and the originally European H. aurantiacum with orange-red flowers (Hickman 1993).

Characters (from J. L. Strother): Perennials, (5–)20–150+ cm; taprooted (rootstocks sometimes woody, branched; stolons produced in some taxa). Stems usually 1, usually erect, usually branched distally, sometimes throughout, sometimes scapiform, glabrous or hairy (induments often complex). Leaves basal, basal and cauline, or cauline; petiolate or sessile; blades mostly elliptic, lanceolate, oblanceolate, oblong, or spatulate, margins entire, denticulate, or dentate (occasionally laciniate to pinnatifid; faces glabrous or hairy, induments often complex). Heads borne singly or in corymbiform, paniculiform, thyrsiform, umbelliform, or nearly racemiform arrays. Peduncles (terminal and axillary) not inflated, often bracteate. Calyculi 0 or of 3–13(–16+), deltate to lanceolate or linear bractlets (in 1–2+ series; sometimes intergrading with phyllaries). Involucres hemispheric or campanulate to cylindric, 3–9[–12+] mm diam. Phyllaries 5–21(–40+) in 2+ series, lanceolate to linear, subequal to unequal (reflexed in fruit), margins usually little, if at all, scarious, apices obtuse to acute or acuminate. Receptacles flat, pitted, glabrous, epaleate. Florets 6–150+; corollas usually yellow, sometimes white or ochroleucous, sometimes tinged with cyan or red, rarely orange (then often drying scarlet or purplish). Cypselae usually red-brown or black (rarely tan), usually more or less columnar or prismatic, sometimes more or less urceolate (slightly bulbous proximally and narrower distally) or nearly fusiform, not distinctly beaked, ribs (or grooves) usually 10, faces glabrous; pappi persistent (fragile), of 20–80+, distinct, white, sordid, stramineous, or rufous, more or less equal or unequal, barbellulate bristles in 1–2+ series. x = 9.

<==Hieracium
    |--H. albidum C55a
    |--H. albiflorum H93
    |--H. amplexicaule C55b
    |--H. annae-toutoniae V98
    |--H. argutum [incl. H. argutum var. parishii] H93
    |--H. aurantiacum C55b
    |--H. bifidum V98
    |    |--H. b. ssp. bifidum V98
    |    `--H. b. ssp. toutonii V98
    |--H. bolanderi H93
    |--H. camkorijense GR98
    |--H. chilense D03
    |--H. chondrilloides C55a
    |--H. glanduliferum C55a
    |--H. gracile H93
    |--H. greenei H93
    |--H. gronovii J87
    |--H. horridum H93
    |--H. jacquini C55a
    |--H. pieroides C55a
    |--H. pilosella AC93
    |--H. piloselloides H91
    |--H. praealtum AC93
    |--H. rotundatum H09
    |--H. scouleri [incl. H. scouleri var. nudicaule] H93
    |--H. tomiasae GR98
    |--H. toutonianum V98
    `--H. umbellatum D51

*Type species of generic name indicated

REFERENCES

[AC93] Atkinson, I. A. E., & E. K. Cameron. 1993. Human influence on the terrestrial biota and biotic communities of New Zealand. Trends in Ecology and Evolution 8 (12): 447–451.

[C55a] Candolle, A. de. 1855a. Géographie Botanique Raisonée: Ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle vol. 1. Librairie de Victor Masson: Paris.

[C55b] Candolle, A. de. 1855b. Géographie Botanique Raisonée: Ou exposition des faits principaux et des lois concernant la distribution géographique des plantes de l’époque actuelle vol. 2. Librairie de Victor Masson: Paris.

[D51] Dobzhansky, T. 1951. Genetics and the Origin of Species 3^rd ed. Columbia University Press: New York.

[D03] Dusén, P. 1903. The vegetation of western Patagonia. In: Scott, W. B. (ed.) Reports of the Princeton University Expeditions to Patagonia, 1896–1899 vol. 8. Botany pp. 1–34. The University: Princeton (New Jersey).

[GR98] Greuter, W., & T. Raus (eds.) 1998. Med-Checklist Notulae, 17. Willdenowia 28: 163–174.

[H09] Heltmann, H. 2009. Der Königstein (Piatra Craiului), die Perle der Burzenländer Gebirge. Mauritiana 20 (3): 515–527.

[H93] Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

[H91] Hubálek, Z. 1991. Biogeographic indication of natural foci of tick-borne infections. In: Dusbábek, F., & V. Bukva (eds) Modern Acarology: Proceedings of the VIII International Congress of Acarology, held in České Budĕjovice, Czechoslovakia, 6–11 August 1990 vol. 1 pp. 255–260. SPB Academic Publishing: The Hague.

[J87] Judd, W. S. 1987. Floristic study of Morne La Visite and Pic Macaya National Parks, Haiti. Bulletin of the Florida State Museum—Biological Sciences 32 (1): 1–136.

[V98] Vogt, R. 1998. Das Hieracium-Herbar von Karl Touton. Willdenowia 28: 253–262.

Last updated: 2 June 2019.