Hieracium L. – Hawkweed s. str. (Hieracium subgen. Hieracium, without Pilosella)
Hieracium s. str. belongs to the most diverse genera of the plant kingdom. This species richness is obviously related to apomictic seed formation, which has been known for a long time in Hieracium s. str. (Murbeck 1904, Ostenfeld & Raunkiær 1903, Ostenfeld 1904 & 1906). The type of apomixis is autonomous diplospory: the embryo sac develops from the spore-forming tissue, the archespore. No fertilization is necessary for the development of the endosperm.
In Germany, there are only two sexual, constantly diploid taxa: H. intybaceum (Schlaginweitia intybaceum) and H. umbellatum. Despite the great morphological variability in the genus (Zahn 1921-1923 & 1922-1938), particularly the occurrence of "intermediate species" − which combine characters of "principal species" − indicate intensive hybridization, sexual reproduction in apomictic Hieracium species has not been shown in Germany so far. Hybridization is also very unlikely due to embryo sac development prior to the opening of flowers (Nogler 1984). Outside of Germany, hybrids exist between diploid species (Merxmüller 1975, Mráz & al. 2005) and between pollen-producing polyploids and diploids. Fehrer & al. (2009) assume that a larger number of extinct diploid species are responsible for the emergence of the overwhelming diversity of polyploid Hieracium species. Hand et al. (2015) demonstrated the meiotic formation of megaspore-tetrads in several tri- or tetraploid species in a maximum of a few percent of the megaspore mother cells. Whether these can develop into embryos, however, is still unknown.
The genus is extraordinarily species-rich. For Europe, Gottschlich (1996) estimated 10,000 to 15,000 taxa. The hardly comprehensible variety of forms has led to an unconventional solution in Central Europe, mainly worked out by Zahn (1906, 1921-1923 & 1922-1938). Principal species have been identified, which are characterized by their unique characters and large-scale areas. Intermediate species form links between one or more principal species without original distinguishing characters. These relationships are expressed in formulas that indicate the position of the intermediate species (e.g. H. porrectum: bifidum < valdepilosum or H. rapunculoides: lachenalii ≤ prenanthoides). All other taxa that can only be distinguished by subtle morphological characteristics are assigned to the principal and intermediate species as infraspecific taxa − subspecies, varieties, sub-varieties, forms or sub-forms. According to this system, in which the species level is used in Rothmaler (Bräutigam 2011), about 90 species occur in Germany. Beyond Germany, this “Zahn system” is applied less and less and, as in other apomictic groups, only the species level is used. As a rule of thumb, it can be said that in Hieracium "the subspecies are the species". If we apply the criteria used in other apomictic groups for species delimitation, we can expect over a thousand species in Germany for Hieracium. In his synopsis of the taxa recorded for Germany, Gottschlich (2020) already lists 101 collective species (principal and intermediate species, see below) with 849 subspecies. Meanwhile, the fine-scale species concept is also beginning to establish in Hieracium, for example Müller (2004) described new taxa on this basis from the surrounding area of Jena. For Gottschlich (1996), the cleaning up of Zahn's "subtle taxonomy" and the "peeling out of morphologically, geographically, and locally tangible taxa" is a wish program for the realization of which there are currently in Central Europe hardly any "means in sight". In particular, the "highly polymorphic" species, such as H. bifidum, H. murorum, H. lachenalii and H. laevigatum can be divided into a multitude of taxa by the application of the micro-species concept.
The separation of Hieracium and Pilosella, which had already been proposed by Schultz & Schultz (1862), became increasingly accepted, although there were still opposing votes. After molecular genetic investigations (Fehrer & al. 2007 & 2009) Schlaginweitia, with S. huteri and S. intybacea, was separated from the genus Hieracium, which had not yet been performed by Bräutigam (2011).
The majority of German Hieracium species inhabit rock habitats in the Alps and low mountain ranges. But many species also find suitable habitats in forest margins and sparse forests. Grassland and ruderal places are rather avoided.
Hieracium is extremely widespread in the northern hemisphere. The area stretches over Central America and even South America. The highest number of species is found in the mountains (Alps, Balkans, Carpathians, Pyrenees).
All types are perennials with erect, usually branched stems. A basal leaf rosette exists in most species. Stem leaves are often only present in small numbers in species with a basal leaf rosette, while often numerous in species without a basal leaf rosette. The leaf blade is always simple and often of lanceolate shape, although there is considerable variability. Single flowers are arranged in heads surrounded by involucral bracts. The super-inflorescences consisting of several heads are usually bifurcate. The involucral bracts are arranged imbricately to almost in two rows. The receptacular scales (bracts of a single flower) are missing. But the cavities in which the flowers, later the fruits, stand usually have tooth-shaped scales at their edges. The ray flowers are without exception yellow. The color of styles varies from yellow to green to mostly blackish. The achenes are cylindrical and generally black-brown. The pappus is dentate and dirty-white to light brown.
There are no modern identification keys available that represent the entire variety of forms of the genus Hieracium. The determination of the " principal and intermediate species" is possible with the keys developed by Bräutigam (2011, Germany), Gottschlich (1996, Baden-Württemberg; 2008, Austria) or Schuhwerk & Lippert (1991, Bavarian Forest).
In order to estimate the variability, 3-5 well-developed plants should always be collected. The occurrence (and collection) of basal leaves is worthy of respect. Style color and leaf coloration, which change during drying, should be noted in the field. Plants with late shoots or late flowers are unsuitable for determination.
For species without a basal leaf rosette, a foliage index is used, which is calculated by dividing the number of cauline leaves by the height of the plant in cm.
A powerful magnifying glass, or better a stereo microscope, is necessary for the determination in order to be able to reliably recognize the proportions of the different hair types.
All taxa mentioned in the 22nd edition of the Rothmaler-Exkursionsflora by Bräutigam (2021) as well as Hieracium entleutneri were included here. Taxa summarized by Bräutigam (2021) with other species are treated separately as far as possible, but are assigned to the corresponding species from the Rothmaler edition in the taxonomic tree. So far, it has not been possible to find reliably determined specimens of all taxa treated in the portal. In the digitized specimens provided, care was taken to ensure that as many subspecies as possible occurring in Germany are presented. For many species, however, only a small part of the subspecies occurring in Germany and their diversity could be taken into account.
Our thanks go to Günter Gottschlich (Tübingen) for providing and revising a large number of specimens. The Bavarian State Collection (M) provided a large share of the specimens, further material we received from Münster (MSTR) and Vienna (W).
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