Taxonomic principles, reproductive systems, population genetics and relationships within selected groups of genus Taraxacum (Asteraceae)

Submitted by vojta on Wed, 11/21/2018 - 16:55

Genus Taraxacum (Asteraceae), having ∼60 sections and 2,800 species, is known for its complicated evolutionary relationships and taxonomy due to processes like frequent hybridization, polyploidization, asexual reproduction, clonality and low structural morphological variability. Various taxonomical concepts and approaches are reviewed, evaluated and discussed from point of view of their ability to deal with such a complicated genera as is Taraxacum. Various processes responsible for the complicated situation within Taraxacum are discussed and reviewed. Section Dioszegia, comprising T. serotinum and its allies, are an exception because only sexuals are reported for all the members of this group. On the basis of the analysis of microsatellite (SSRs) variation, distribution and morphology, we addressed problems related to their mode of reproduction, among-population relationships, taxonomy and withinpopulation variation. As a rule, outcrossing was the dominant mode of reproduction, with one notable exception: T. serotinum subsp. tomentosum (≡ T. pyrrhopappum) was autogamous and not heterozygous. A taxonomic revision of sect. Dioszegia recognizes T. serotinum subsp. serotinum (including an aberrant taxon, newly described as var. iranicum), T. serotinum subsp. tomentosum and T. haussknechtii. There has been a decrease in the ability of biologists to identify their material correctly, particularly plants of complicated genera with common agamospermy, where old clonal entities are accorded the rank of species (microspecies), like Taraxacum. Agamospermous microspecies are taxonomic entities recognizable from one another by a set of minute morphological features. The knowledge of microspecies is confined to a few specialists. A selection of nine widespread, generally recognized agamospermous microspecies of Taraxacum sect. Taraxacum, which are characterized by means of eight microsatellite loci, were used to evaluate the ability of four European Taraxacum specialists to identify these microspecies consistently. With two exceptions (and one unclear result) for 125 plants coming from an area extending from Finland to central Europe, the experts identified the microspecies consistently, exclusively on the basis of morphological differences. The within-species microsatellite variation corresponded to the mutational clone cluster hypothesis, with a single unclear result. Each microspecies consisted of one, more or less dominant, clone and several minority clones, each usually confined to a single plant. The Taraxacum flora of the West Himalaya represents one of the dandelion diversity hotspots, with at least 17 sections and about 150 known species. A number of names published from that region were referred to T. sect.Orientalia Handel-Mazzetti in the literature. All these names are revised and newly interpreted, with emphasis on plants erroneously determined as T. stenolepium. An nrDNA ITS sequence analysis including the only sexual member of T. section Squamulosa and the other sexual taxa known in Taraxacum shows a separate position of T. sect. Squamulosa. The new section is compared with sections Primigenia, Coronata and Orientalia. Taraxacum koksaghyz, dandelion from steppes of Kazakhstan, has been known for long time as potential rubber producer, possibly replacing currently the most popular rubber producing tropical tree Hevea brasiliensis. We evaluate its closely related congener, Taraxacum bicorne. Its taxonomy is reviewed, population genetic characteristic evaluated, and rubber content of the two species is compared. For the rubber extraction we modified existing method to require minimal amount of material. Taraxacum bicorne is shown to be outcrossing sexual diploid and its rubber content is about half of that of T. koksaghyz (∼3.2% vs. ∼7.2%), but because of relatively robust constitution of T. bicorne in comparison to T. koksaghyz, T. bicorne could be used as potential rubber source. The taxonomy, micromorphology, karyology and evolutionary relationships of Taraxacum bithynicum DC. were studied using the original material and new samples from the summit area of Mt. Uludağ, Bursa Province, Turkey. It is sexual with 2n = 16, considerably isolated in outer phyllary and achene characters. The nrDNA ITS NeighborNet analysis shows relationships of T. bithynicum with members of sect. Scariosa. Taraxacum bithynicum is considered as a taxon endemic to the summit area of Uludağ. All these case studies shed more light on the taxonomy, population genetics and undergoing mechanisms within genus Taraxacum — real touchstone of plenty of biological concepts, theories and methods.