The taxonomy of the genus Taraxacum is generally considered to be extremely difficult and complex. Reasons for this are the weak morphological differentiation within the very species-rich and widespread genus, the high proportion of agamospermic representatives, the frequent coexistence of agamospermic and sexual species, complex hybridizations, and polyploidy (Kirschner et al. 2003, Záveská Drábkovà et al. 2009, Štěpánek & Kirschner 2012a, Zeisek et al. 2015).

In agamospermy, seed formation takes place without fertilization of the egg cell. It thus corresponds to the apomixis definition of Nogler (1984: apomixis = asexual reproduction by seeds, "seed apomixis "), which is why both terms are treated in the following as synonyms (see Richards 2003). In Taraxacum, agamospermic seed formation occurs through the development of the female gametophyte (embryo sac) from an unreduced embryo sac mother cell, which is formed by a non-reducing form of meiosis (restitution nucleus formation), and the subsequent parthenogenetic development of the egg cell (diplospory-parthenogenesis, diplospory of the Taraxacum-type; see Nogler 1984).

Multiple hybridization events, particularly involving diploid and polyploid, sexual and agamospermic taxa, play an important role in the evolutionary history of most Taraxacum taxa (King 1993, Kirschner & Štěpánek 1996, Kirschner et al. 2015). Experiments have shown that the offspring from the crossing of a sexual diploid (2n = 16) and a sexual tetraploid (2n = 32) species were triploid (2n = 24) and predominantly sterile (Kirschner & Štěpánek 1996). The authors interpret these offspring as "raw material" for the development of agamospermic groups, whereby sterility is overcome by the development of agamospermy. Taxa with higher ploidy levels may have resulted from spontaneous duplications of chromosome sets (autopolyploidy) or crossings with apomictic plants of higher ploidy levels (allopolyploidy). Crossings between sexual and agamospermic taxa are possible because sexual species can be pollinated by pollen from apomicts.

The majority of Taraxacum species are representatives (microspecies) of polyploid-apomictic, interlinked swarms of forms, which are classified as sections (previously treated as aggregates) (Uhlemann 2001, Uhlemann et al. 2016). In addition to a few groups with purely sexual species, regarded as phylogenetically early splitting lineages, there are some evolutionarily recent sections with exclusively polyploid apomictic representatives (in Germany e.g. sect. Celtica, sect. Cucullata, sect. Hamata, sect. Naevosa) and several sections comprising apomictic as well as sexual species (e.g. sect. Taraxacum, sect. Erythrosperma, sect. Rhodocarpa (=Alpestria), sect. Obliqua, sect. Palustria; sexual representatives of the latter three are only found outside of Germany; within sect. Erythrosperma, the occurrence of sexual species in Germany is questionable; Kirschner et al. 2015, Uhlemann et al. 2016).

A frequent phenomenon within the genus is the so-called geographical parthenogenesis: apomictic species have larger distributional areas than their sexual relatives, reaching further north and higher altitudes (Bierzychudek 1986, Hörandl 2006, Kirschner et al. 2015). In Northern Europe, North America, and Siberia, agamospermy is therefore the dominant reproductive system within the genus (Kirschner & Štěpánek 1996). The Pleistocene Ice Ages are discussed as one of the main causes for this distribution pattern and also for the formation of apomictic taxa. Hörandl (2006) assumes the origin of the apomicts as being predominantly in the peripheral areas of the Pleistocene glaciers, where extensive fluctuations in range expansion offered favorable conditions for hybridization and polyploidization. The faster seed development and the higher number of seeds, as well as independence on pollinators and the production of genetically identical offspring, are also seen as adaptive advantages of agamospermic species, which have enabled them to colonize the ice-free areas more quickly during the retreat of the glaciers and which still favor them over sexual taxa at higher latitudes and altitudes (Nijs & Sterk 1984, Hörandl 2006). In Europe, the distribution limits of the sexual diploid Taraxaca largely coincide with those of the Pleistocene ice-free areas (Uhlemann 2001).

In Germany, three reproduction systems can be distinguished within the genus: (i) obligate agamospermic species, (ii) facultative agamospermic species and (iii) sexual species (Uhlemann 2001, Uhlemann et al. 2016). Polyploid, obligate apomicts occur throughout Germany, and in most parts of the country (North German Lowlands, most of the low mountain ranges except South West German Scarplands) they are the only representatives of the genus. Diploid, obligate sexual species are restricted to Baden-Württemberg, South Hesse (Odenwald) and South West Bavaria, with the exception of T. bessarabicum, wich occurs inconsistently near Mainz. In the rest of Bavaria, east of a line Frankfurt (Main)-Augsburg-Innsbruck (Jenniskens et al. 1984), facultative apomictic representatives can be found in addition to the obligate agamospermic Taraxaca (see Map 3 in Uhlemann 2001). These triploid individuals develop 10-15% sexual flowers per head (Jenniskens et al. 1984).

An unambigous determination of Taraxacum species is only possible in areas with exclusively obligate apomictic taxa (Uhlemann 2001, Uhlemann et al. 2016). In the other regions, in addition to stable agamospermic species, hybrids between sexual and obligate agamospermic or rather, between facultative and obligate agamospermic taxa also occur.

Section Palustria (marsh dandelions) includes, in addition to predominantly agamospermic, also two sexual species (T. raii, T. tenuifolium; Kirschner & Štěpánek 1998). These occur in southern France and in the northwestern catchment area of the Adriatic Sea (NW-Italy, W-Slovenia, Croatian, and Bosnian Adriatic coasts). Only obligate apomicts are known from Germany within this section so far. A partially sexual or rather, facultative agamospermic reproduction probably takes place in Eastern European populations of T. vindobonense (Kirschner & Štěpánek 1998).

The genus Taraxacum currently comprises approx. 2,800 species and about 60 sections (Kirschner et al. 2015, Zeisek et al. 2015). Section Palustria contains approx. 125 species.

The section is the most important supraspecific taxon within the genus. The genus’ division into sections, however, is partly problematic since there are not only principal species which correspond to the section’s descriptions, but also probably hybridogenic species which are morphologically intermediate between two or more sections (Uhlemann 2002, 2003, Uhlemann et al. 2016). These could be classified as taxa of an uncertain systematic position or treated as morphologically uniform groups with preliminary working names (Uhlemann 2002, 2003).

According to the 11th edition of the Critical Volume of Rothmaler Field Flora (Müller et al. 2016), there are 412 described Taraxacum species known in Germany (estimated ≈ 30% of the real number of species), which are assigned to 13 sections and at least three further groups with possible sectional rank (Uhlemann et al. 2016). With 29 species, the marsh dandelions (sect. Palustria) represent the third largest section of the German Taraxacum flora, which may also be due to their good status of research.

A group frequently separated from the core Palustria is T. subalpinum group (Hudziok group, palustroids). The group comprises five species in Germany (as well as a larger number of undescribed or unidentified species) and is morphologically and ecologically intermediate between the sections Palustria and Taraxacum. In contrast to the species of the section Palustria, these taxa differ by a more robust habit and more deeply lobed leaves (Uhlemann et al. 2016). With the exception of T. copidophyllum Dahlst., Kirschner & Štěpánek (1998) treat all species in this group as representatives of the Palustria section. In his treatment of the marsh dandelions of southern Germany, Schmid (2003) considers T. subalpinum Hudziok to belong exclusively to the section, since its outer involucral bracts, which have only a narrow membranous margin, at least correspond in shape and size to those of the typical representatives of the Palustria section. Uhlemann et al. (2016) treat the entire group separately from the Palustria section. Nowadays, T. subalpinum , together with some other species not found in Germany, is assigned to the section Austropaludosa, newly described by Štěpánek & Kirschner (2021).

The genus Taraxacum occurs worldwide in temperate climate zones, but has a distributional focus on the temperate to subarctic regions of the Northern Hemisphere (Kirschner et al. 2015, Vašut & Trávníček 2004). Their representatives colonize a multitude of different habitats (Richards 1970). The center of diversity, which Doll (1982) also considers to be the origin of the genus, is found in the mountains of Central Asia.

The section Palustria is native to Europe and the northern Near East, whereby most species can be found in southern Central and Southern Europe (Kirschner & Štěpánek 1998). The species colonize mainly low-competitive, seasonally damp to wet sites on mineral-rich soils. These include among others extensively used, damp and wet meadows, calcareous swamps and lowland moors (fens) and inland salt meadows (Kirschner & Štěpánek 1998, Schmid 2003, Jung & Huck 2007, Horn 2010). Most of these habitats are endangered, which is why most of the species in the section are threatened.

Taraxacum species are perennial, herbaceous, latex-bearing plants with a single-headed, hollow stalk and taproot-like turnips. The leaves are entire, dentate or lobed, and arranged in a basal rosette. The head, consisting of many ray flowers, has a two-rowed involucre. The inner involucral bracts are linear and always upright, the outer ones shorter and usually broader, adjacent to the inner ones or recurved. The diaspores are subdivided into three parts: the colored fruit (achene), the uncolored rostrum ("umbrella stem") and the pappus consisting of a wreath of unfeathered hairs. The cylindrical to spindle-shaped achenes consist of an usually prickly achene body with an unarmed, conical or cylindrical tip (pyramid).

The species of sect. Palustria are delicate, small to medium-sized plants (5-30 cm). Their unspotted leaves are entire, dentate, sinuate, curved, or have only a few small lobes (almost all other native Taraxacum species usually have deeply lobed leaves). The petioles are narrow and usually wingless, rarer slightly winged. The flower heads stand upright during florescence. Their adjacent to upright protruding outer involucral bracts consist of three zones: a darkly colored centre, a lighter colored area towards the margin, and a narrow transparent membranaceous margin. The flat ligulate flowers are light- to deep yellow, their styles dirty greenish-yellow (yellowish stylodium with darkly pigmented bristles), light grayish-yellow (yellowish stylodium with unpigmented bristles), or dark green. The gray to straw-colored achenes usually have ± cylindrical, rarer almost conical pyramids. The pappus of the marsh dandelions is pure white.

(see Zehm & Horn 2009, Schmid 2003, Uhlemann 1992, 2003, Uhlemann et al. 2016)

Taraxacum specimens should only be collected during the main flowering period: April-May (lowlands and low mountain ranges), June-August (very high mountain sites and Alps). In no case should fruiting specimens or autumn specimens exclusively be collected, as the leaf morphology changes at late stages of development. It is best to cut off the plants directly under the rosette so that the rosette and flower head remain connected, but also that regrowth from the rootstock is possible. For species conservation reasons Zehm & Horn (2009) recommended to only remove plants from the population of marsh dandelions that have several individuals (10-20) in the vicinity. Ideally, the plants should have fresh leaves, one opened and one unopened inflorescence, and, a ripe infructescence. For this reason, 2-3 intact plants from a population should be collected. Only approx. 5 leaves are kept on the rosette for the herbarium voucher since the leaf characteristics of complete leaf rosettes are difficult to recognize due to overlapping and the plants then also dry worse. In general, Taraxacum specimens are usually very damp and the drying paper, must therefore either be changed frequently or their drying is supported by a fan. After collecting, they should also be transferred to the press very quickly, as the leaves can fold in the collection bag. If necessary, the leaves must be unfolded after a pre-press. When pressing, moderate pressure should be used because otherwise the involucral bracts will soon no longer be clearly discernible.

For Taraxacum, 30-50 individual characters are commonly used to characterize a taxon. The following is a list of the most important characters relevant for determination (cf. Fig. 2 Uhlemann 2003), whereby the characters particularly important for the Palustria section are highlighted in bold:

• Leaf (hairiness, color, spotting, shape, rippling, lobes)
• Petiole (color, wing)
• Leaf midvein (hairiness, color, presence of stripe pattern)
• Leaf end lobes (shape, size)
• Leaf side lobes (orientation, shape, teeth, cleft)
• Leaf sinus (color, shape, rippling, teeth)
• stalk (hairiness, color)
• Flower heads (size)
• Involucre (shape, pruinescence, color)
• Outer involucral bracts (number, orientation, margin, width, color, shape, length, callosity)
• Flowers (color, coloring of the stylodia, coloring of the teeth, shape, presence of pollen)
• Fruit (color, shape, size, teeth) (Note: always determine characteristics on ripe fruits)
• Pyramid (shape, length)
• Rostrum (thickness, length)

The seasonal variability of leaf morphology has already been pointed out. Furthermore, it should be noted that some characteristics may also be subject to local modifications. According to Schmid (2003), this applies to the marsh dandelions, for example:

• Leaf morphology – stronger lobation and dentation in dry habitats vs. more frequently unlobed leaves in flooded specimens
• Indumentum of stalks – in some species stronger in dry locations
• Colour of stalk and petiole – many species tend to be more pale at damp and nutrient-rich locations
• Flower heads – tend to be larger at nutrient-rich sites
• Outer involucral bracts – at very nutrient-rich locations they can be slightly protruding to loosely attached in all species
• Fruits – often larger, more prickly, more intensively colored and with a longer rostrum at more damp and nutrient-rich locations

The fruits of Taraxacum also vary within a fructescence. The outer achenes are larger, thicker, and very prickly.

The portal contains all species of the section Palustria treated by Uhlemann et al. (2016) as well as Taraxacum ciliare Soest recorded for Germany in 2009 (Meierott 2017). The given specific characters are essentially taken from Schmid 2003, Kirschner & Štěpánek 1998 and Uhlemann et al. 2016. In addition, the studies of Dahlstedt (1905, 1933), van Soest (1942, 1956, 1961, 1965), Haglund (1946), Hudziok (1965, 1967, 1969), Kirschner & Štěpánek (1986, 1992, 1994) as well as Štěpánek & Kirschner (2012b) were consulted.

The profiles of the individual species contain links to the respective species pages on FloraWeb. We would like to point out that in the case of Taraxacum, the photo pages linked to FloraWeb contain several misidentifications.

We would like to thank the Herbarium of the State Museum of Natural History in Stuttgart (STU), the Herbarium of the Martin-Luther University in Halle (HAL), and the Botanical State Collection in Munich (M) for providing instructive specimens.

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Datenbankeintrag zum Gattungstypus

Cichorieae Portal

Wesenberg, J. & Uhlemann, I. 2016 (aktualisiert 2024). Taraxacum F. H. Wigg. sect. Palustria (H. Lindb.) Dahlst. In: Dressler, S., Gregor, T., Hellwig, F. H., Korsch, H., Wesche, K., Wesenberg, J. & Ritz, C. M. Bestimmungskritische Taxa zur Flora von Deutschland. Herbarium Senckenbergianum Frankfurt/Main, Görlitz & Herbarium Haussknecht Jena. [online] https://bestikri.senckenberg.de