Hieracium (),[
]
which are part of the tribe Cichorieae. Hawkweeds, with their 10,000+ recorded species and subspecies,[
]
Some botanists group all these species or subspecies into approximately 800 accepted species,[
]
while others prefer to accept several thousand species. Since most hawkweeds reproduce exclusively asexually by means of 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 (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
Flowers and flower-heads
Hieracium or
hawkweeds, like others in the family Asteraceae, mostly have
yellow,
tightly packed flower-heads of numerous small flowers
but, unlike
Bellis perennis and
in the same family, they have not two kinds of
but only strap-shaped (
spatulate) florets, each one of which is a complete
flower in itself, not lacking stamens,
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.
Bracts, stems and leaves
Erect single,
glabrous or hairy
Plant stem, 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; "Trichome" or surfaces with scattered to crowded, 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, peduncle, and bract may be glabrous or may bear one, two, or all three of the types of hairs mentioned above.
Like the other members of the Cichorieae, hawkweeds contain a milky latex.
Ecology
The large yellow underwing moth (
Noctua pronuba) feeds on
Hieracium species.
Distribution
Hieracium species are native to
Africa,
,
Europe,
North America,
and
South America.
Species
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.
Europe
-
Hieracium lachenalii - Common hawkweed
-
Hieracium attenboroughianum – Attenborough’s hawkweed
-
Hieracium bakerianum
-
Hieracium hethlandiae – Cliva Hill hawkweed
-
Hieracium lepidulum Stenstr. ex Dahlst. – tussock hawkweed
-
Hieracium lucidum Guss. – Sicilian sparviere
-
Hieracium insolitum (Zahn) Üksip
-
Hieracium villosum Jacq.
North America
The list below is a selection of species that have been accepted by the USDA Natural Resources Conservation Service
and Canada.
[ Key to Identification of Invasive and Native Hawkweeks ( Hieracium spp.) in the Pacific Northwest , BC Ministry of Forests]
A more complete list is given in the list of
Hieracium species.
-
Hieracium albertinum – houndstongue hawkweed
-
Hieracium albiflorum Hook. – white hawkweed
-
Hieracium × alleghaniense Britt. (pro sp.)
-
Hieracium argutum Nutt. – southern hawkweed
-
Hieracium × atramentarium (Naegeli & Peter) Zahn ex Engl. (pro sp.)
-
Hieracium atratum Fries – polar hawkweed
-
Hieracium bolanderi Gray – Bolander's hawkweed
-
Hieracium × brachiatum Berth. ex DC.
-
Hieracium canadense Michx. – Canada hawkweed
-
Hieracium carneum Greene – Huachuca hawkweed
-
Hieracium × fassettii Lepage
-
Hieracium fendleri Schultz-Bip. – yellow hawkweed
-
Hieracium × fernaldii Lepage
-
Hieracium × fuscatrum Naegeli & Peter (pro sp.)
-
Hieracium glomeratum Froel. – queen-devil hawkweed
-
Hieracium gracile Hook. – slender hawkweed
-
Hieracium greenei Gray – Greene's hawkweed
-
Hieracium greenii Porter & Britt. – Maryland hawkweed
-
Hieracium × grohii Lepage
-
Hieracium gronovii L. – queendevil
-
Hieracium horridum Fries – prickly hawkweed
-
Hieracium kalmii L. – Kalm's hawkweed
-
Hieracium lachenalii K.C. Gmel. – common hawkweed
-
Hieracium laevigatum Willd. – smooth hawkweed
-
Hieracium lemmonii Gray – Lemmon's hawkweed
-
Hieracium longiberbe T.J. Howell – longbeard hawkweed
-
Hieracium longipilum Torr. – hairy hawkweed
-
Hieracium maculatum Sm. – spotted hawkweed
-
Hieracium marianum Willd. – Maryland hawkweed
-
Hieracium megacephalum Nash – coastal plain hawkweed
-
Hieracium murorum L. – wall hawkweed
-
Hieracium paniculatum L. – Allegheny hawkweed
-
Hieracium parryi Zahn in H.G.A. Engler – Parry hawkweed
-
Hieracium piloselloides Vill. – tall hawkweed
-
Hieracium praealtum Vill. ex Gochnat – kingdevil
-
Hieracium pringlei Gray – Pringle's hawkweed
-
Hieracium robinsonii (Zahn) Fern. – Robinson's hawkweed
-
Hieracium rusbyi Greene – Rusby's hawkweed
-
Hieracium sabaudum L. – New England hawkweed
-
Hieracium scabrum Michx. – rough hawkweed
-
Hieracium schultzii Fries – roughstem hawkweed
-
Hieracium scouleri Hook. – Scouler's woollyweed
-
Hieracium scribneri Small – Scribner's hawkweed
-
Hieracium traillii – Maryland hawkweed
-
Hieracium triste Willd. ex Spreng. – woolly hawkweed
-
Hieracium umbellatum L. – narrowleaf hawkweed
-
Hieracium venosum L. – rattlesnakeweed
Some species are now placed in the genus Pilosella:
-
Hieracium aurantiacum L., syn. of Pilosella aurantiaca – orange hawkweed
-
Hieracium caespitosum Dumort., syn. of Pilosella caespitosa – meadow hawkweed
-
Hieracium flagellare Willd., syn. of Pilosella flagellaris – whiplash hawkweed
-
Hieracium floribundum Wimmer & Grab., syn. of Pilosella floribunda – kingdevil hawkweed
-
Hieracium lactucella Wallr., syn. of Pilosella lactucella – European hawkweed
-
Hieracium pilosella L., syn. of Pilosella officinarum – mouse-ear hawkweed
Plant pest
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.
It is a particular threat in alpine ecosystems previously dominated by native tussocks, though it will colonise habitats from bare ground, to exotic
Pinus radiata forest, to
Nothofagus forest.
In the United States, many species of Hieracium have been introduced and all species present are considered noxious weeds in one or more states.
In Australia, hawkweeds are invasive pests in alpine regions, all species of Hieracium are listed or declared under various State Acts.
Further reading
-
-
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
