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Published In: Species Plantarum 2: 799. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 8/10/2009)

 

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36. Hieracium L. (hawkweed)

Plants perennial herbs, with rhizomes or a short, hard rootstock and fibrous roots. Latex white. Stems usually solitary (sometimes few to several in H. caespitosum), erect or strongly ascending, unbranched below the inflorescence, finely ridged, often noticeably spreading-hairy (the hairs with a bulbous or slightly expanded base), at least toward the base, sometimes also with minute, stellate hairs and/or gland-tipped hairs. Leaves basal and sometimes also alternate, hairy or sometimes nearly glabrous, sessile or short- to long-petiolate. Leaf blades unlobed, narrowly oblanceolate to obovate, those of the uppermost leaves sometimes oblong-lanceolate to oblong-ovate, the margins otherwise entire, with 1 main vein visible and often also a pinnate pattern of secondary veins (these sometimes forming a network), occasionally also a faint network of anastomosing tertiary veins. Stem leaves gradually reduced in size, sometimes only produced toward the stem base, without a pair of narrowly triangular, clasping lobes at the base. Inflorescences terminal panicles or racemes, sometimes appearing as loose clusters at the stem tip. Involucre not or only slightly elongating as the fruits mature, narrowly to broadly cup-shaped, the bracts 20–35 or more, arranged variously, generally in 1 or 2 inner series and usually 1 or more additional shorter, outer series, the inner series more or less similar in size, the narrow margins sometimes thin and pale, the tip ascending at flowering. Receptacle with minute, broadly triangular scales around the base of each floret, these fused into an irregular low ridge or wing. Ligulate florets 20 to more than 100 per head. Corollas light yellow to bright yellow (orange to reddish orange elsewhere). Pappus of more or less numerous bristles, these appearing smooth but microscopically barbed, white or straw-colored to light yellowish to orangish brown. Fruits nearly cylindrical to narrowly oblong-elliptic in outline, not beaked, not flattened, circular or finely angled in cross-section, with (8–)10 longitudinal ribs, these appearing smooth or nearly so (microscopically cross-wrinkled), glabrous, purplish brown to nearly black, the pappus attached to a relatively broad but not or only slightly expanded tip. About 100 to many more than 1,000 species, North America to South America, Caribbean Islands, Europe, Asia, Africa.

The species of Hieracium native to North America are generally well behaved biologically, aside from occasional interspecific hybridization. However, in the Old World, particularly in Europe, where polyploidy and apomixis are pervasive, the formal taxonomic description of various minor forms and races as so-called microspecies has led to an incredible nomenclatural proliferation involving thousands of published species epithets. This has tended to preclude precise estimates of species numbers in the genus.

Unfortunately, several of the Old World species have become important weeds of pastures and natural grasslands in the United States. Thus far, only one of these has begun to make inroads into Missouri (see below).

 

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1 1. Stems and leaves with the spreading hairs mostly 1020 mm long ... 3. H. LONGIPILUM

Hieracium longipilum
2 1. Stems and leaves with the spreading hairs 19 mm long

3 2. Fruits 1.52.0 mm long; pappus bristles white; stem leaves only 1 or 2 toward the stem base; plants frequently producing stolons, often appearing in dense patches of rosettes ... 1. H. CAESPITOSUM

Hieracium caespitosum
4 2. Fruits 24 mm long; pappus bristles light yellowish to orangish brown; stem leaves often 3 or more, often extending above the stem base for some distance (sometimes few and nearly basal in H. gronovii); plants not producing stolons, not appearing colonial

5 3. Basal leaves usually present at flowering; ligulate florets 2040; fruits narrowly ellipsoidal, somewhat tapered to a slightly expanded tip ... 2. H. GRONOVII

Hieracium gronovii
6 3. Basal leaves withered at flowering; ligulate florets 40100 or more; fruits more or less cylindrical, not tapered or narrowed at the unexpanded tip ... 4. H. SCABRUM Hieracium scabrum
 
 
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