Pollen diversity in the genus Carlina L. (subtribe Carlininae, Compositae) and its systematic significance
Introduction
Carlina L is a well-defined genus belongs to the tribe Cardueae, subtribe Carlininae of Compositae. The Cardueae are known commonly as “thistles” and plants of Carlina are known as “carline thistles.” The genus is medium-sized, comprising a number of species and infrageneric taxa with estimates of 28 species, 12 subspecies, and 14 varieties according to Kovanda (2002) and Susanna and Garcia-Jacas (2007), and 34 accepted species, 12 subspecies, and 7 varieties, according to The Plant List (2013). The genus is distributed from the Canary Islands and the Mediterranean (across Europe and northern Africa) to temperate Asia (central Siberia and northwestern China) (Kovanda, 2002, Peng et al., 2012). Meusel and Kästner (1994) divided the genus Carlina into five subgenera, Carlina, Carlowizia, Heracantha, Lyrolepis, and Mitina, with an underlying hierarchy of sections and subsections.
In their monograph of the genus, Meusel and Kästner, 1990, Meusel and Kästner, 1994 provided a review of Carlina that covered their leaf morphology, inflorescence, flower and fruit, chorology, ecology, karyology, embryology, palynology, chemistry of secondary compounds, and taxonomy. A molecular phylogeny of the genus has been established (Susanna et al., 2006, Wahrmund et al., 2010).
Palynological studies have been helpful tools in taxonomical revisions of numerous genera of Compositae and the Cardueae in particular (Bolick, 1978, Bordbar and Mirtadzadini, 2015, De Leonardis et al., 1984, Garnatje and Martín, 2007, López, 1981, Osman, 2009, Ozler et al., 2009, Pehlivan, 1995, Petit et al., 2001, Punt and Hoen, 2009, Shabestari et al., 2013, Skvarla et al., 1977, Skvarla and Turner, 1966, Stix, 1960, Velari, 1982, Wagenitz, 1976, Wagenitz, 1955).
To date details of pollen morphology are limited to only a few species of Carlina as part of studies at the family and tribal level and in the description of certain species (Beug, 2004, Dimon, 1971, Dittrich, 1977, La-Serna Ramos et al., 1999, Meusel et al., 1984, Petit, 1997, Punt and Hoen, 2009, Stix, 1960, Terrab et al., 2001, Tormo et al., 1984, Valdés et al., 1987).
In this study, we detail pollen morphological characters of 24 taxa of Carlina (19 species, 4 subspecies, and 1 variety). From this data set we assess pollen morphological support for the current infrageneric classification of Carlina. Provision of an identification key to species using pollen is aimed at further applications in other taxonomic studies as well as expanding the palynological knowledge base of the Compositae.
Section snippets
Pollen materials
Pollen grains of the studied species of Carlina were extracted from fertile anthers of flowers in anthesis and/or from buds in pre-anthesis, derived from 26 herbarium specimens of 24 taxa deposited in MSB Herbarium at the Ludwig–Maximilians–Universität München, Germany (herbarium acronyms follow Thiers, 2017) (Table 1). Nomenclature of the studied species was updated according to APG III (2009) and the Kew Garden plantlist website (The Plant List, 2013).
Light microscopy (LM)
For light microscopy, pollen material was
General pollen morphology
Pollen grains of the studied taxa of Carlina are quite homogeneous in their characters. Main features of the analyzed pollen grains of 19 species, 4 subspecies, and 1 variety of Carlina are summarized in detail in Table 2, Table 3, Table 4, Table 5 and Plate I, Plate II, Plate III, Plate IV, Plate V.
Pollen grains are monads and 3-zonocolporate. Most of the studied taxa of Carlina have a sub-spheroidal shape. Among other taxa, prolate (C. acanthifolia, C. biebersteinii subsp. brevibracteata, C.
Discussion
Pollen of the taxa of Carlina studied are consistently 3-zonocolporate monads with elongate ectoapertures and echinate ornamentation. The taxa are diverse in shape (sub-spheroidal, sub-prolate, prolate, or prolate-spheroidal), polar view area (small, medium, or large), length of ectocolpus, tectum ornamentation pattern, and P/E ratio. These results are in agreement with the findings of Tormo et al. (1984) and Punt and Hoen (2009).
Although morphologically pollen grains of the studied taxa of
Conclusion
This study contributes to the understanding of pollen diversity in Carlina with substantial variation across a range of characters. The palynological characters of the studied taxa serve for the identification and classification of taxa at the specific level. The qualitative and quantitative pollen characters provide a helpful taxonomic key for the isolation of closely related species. Further work will be required to determine if the significant differences between single samples of the
Declaration of Competing Interest
The authors declare that there is no conflict of interest regarding the publication of this article.
Acknowledgments
We would like to express our deep gratitude to the director of MSB Herbarium for allowing the study of their specimens. Sincere thanks to Dr. Murray Fagg, Australian National Herbarium & Australian National Botanic Gardens, Canberra, Australia, Dr. W.R. (Bill) Barker and Dr. Robyn Barker, the State Herbarium of South Australia for their diligent proofreading and comments which improved this manuscript. Sincere thanks and deepest appreciation to Dr. Jennifer A. Tate, Senior Lecturer in Plant
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