Systematics of the Amaranthaceae and evolution of pollen characters
Final Report Abstract
The Amaranthaceae are one of the large families of the flowering plant order Caryophyllales and comprise about 900 species in about 80 genera. The family is largely centered in the tropics and subtropics with most of the species diversity in the Mexican highlands and Mesoamerica, in South America (Andes, Chaco and Cerrado), in tropical East Africa and southern Africa as well as in Australia. Amaranthaceae have adapted to a wide spectrum of habitats as trees, lianas, shrubs and herbs. Amaranthaceae stand out in terms of their diverse pollen morphology. They also exhibit physiological specializations, and comprise a large number of species with C4 photosynthesis. The overall goal of this project was a better understanding of the evolution and diversity of the Amaranthaceae. The project was carried out in collaboration with partners in particular in Bolivia, Ethiopia, Kenya and Mexico. Within the project we have generated a well resolved and statistically supported phylogenetic hypothesis for the Amaranthaceae s.str. The family is monophyletic. The closest relatives are a core clade of Chenopodiaceae and a clade comprising the subfamily Polycnemoideae (of Chenopodiaceae), whereas the respective positions of these three clades remain unresolved. Our combined analysis of sequence data from the trnK group II intron (including the matK gene), the rpl16 group II intron and the trnL-F region (group I intron and spacer) contains nearly all genera and a large proportion of the species. Phylogenetic trees inferred from the nuclear ribosomal ITS region were largely congruent, although less resolved at deeper nodes. The genera Bosea and Chamissoa branch first, whereas the mostly New World Gomphrenoideae constituts the largest clade within the family, followed by the largely African Achyranthoid clade. Time divergence estimates using the molecular phylogenetic trees indicate an origin of the Amaranthaceae s.str in the early Eocene. The Gomphrenoideae started to diversify at c. 28 Ma and the Achyranthoid clade at c. 22 Ma. The metareticulate pollen architecture arose in the common ancestor of the core Gomphrenoideae, after the divergence of the Iresinoid clade. Stellate pore ornamentation is derived multiple times within the Achyranthoid clade. Several pollen character states are synapomorphic for major lineages within the family, and can often be used to diagnose genera and even species. The largely African Achyranthoid clade evolved modified sterile flowers serving epizoochory as adhesive structures. This trait did not influence net species diversification rates. The clade comprising Gomphrena and relatives has evolved inflorescence structures that characterize major species groups as synapomorphies. C4 photosynthesis originated at least five times in Amaranthaceae. A new genus level classification of the Amaranthaceae was published in 2015, and is dynamically updated online using the EDIT platform for cybertaxonomy. Using the Amaranthaceae as a model, this project was instrumental for developing a new classification of the Caryophyllales, building upon an international network of colleagues who work in the respective groups (www.Caryophyllales.org). A comparison to the pre-phylogenetic classification of the 1990ies shows significant progress which led to the acceptance or description of new genera and affected taxon concepts for the majority of genera with the premise to accept well-defined monophyletic taxa as genera. A comprehensive species level treatment in Iresine is complete, but is very advanced also for many other genera and is continuously being added to the online portal. Moreover, many species were described as new for science. In line with new field records, improved annotation of specimens in herbaria, the knowledge on the diversity of Amaranthaceae in many parts of the world has considerably grown, and can support conservation and sustainable use of this group of flowering plants.
Publications
- 2003: Phylogeny of Amaranthaceae and Chenopodiaceae and the evolution of C4 photosynthesis. – Int. J. Pl. Sci. 164: 959-986
Kadereit G, Borsch T., Weising K. & Freitag H.
- 2005: Dos nuevas especies de Gomphrena (Amaranthaceae, Gomphrenoideae) de los valles secos de Bolivia. – Novon 15: 180-189
Ortuño T. & Borsch T.
- 2005: Phylogenetics of Amaranthaceae using matK/trnK sequence data – evidence from parsimony, likelihood and Bayesian approaches. – Ann. Missouri Bot. Gard. 92: 66-102
Müller K. & Borsch T.
- 2005: Stellate pore ornamentation in Amaranthaceae pollen: Multiple origins of a unique feature. – Grana 44: 266-281
Müller K. & Borsch T.
- 2006: A further new species of Gomphrena (Amaranthaceae, Gomphrenoideae) from the dry valleys of Bolivia. – Kew Bull. 61: 565-568
Ortuño T. & Borsch T.
- 2007: The taxonomic distribution of C4 photosynthesis in Amaranthaceae sensu stricto. – Amer. J. Bot. 94: 1992-2003
Sage R., Sage T.L., Pearcy, R.W. & Borsch T.
- 2009: trnL-F and rpl16 sequence data and dense taxon sampling reveal monophyly of unilocular anthered Gomphrenoideae (Amaranthaceae) and an improved picture of their internal relationships. – Syst. Bot. 34: 57-67
Sánchez del-Pino I., Borsch T. & Motley T.
- 2011: Phylogenetics of the neotropical liana genus Pedersenia (Amaranthaceae: Gomphrenoideae) and discovery of a new species from Bolivia based on molecules and morphology. – Willdenowia 41: 5 – 14
Borsch T., Ortuño Limarino T. & Nee M. H.
(See online at https://dx.doi.org/10.3372/wi.41.41101) - 2012: Molecular phylogenetics of Alternanthera (Gomphrenoideae, Amaranthaceae): resolving a complex taxonomic history caused by different interpretations of morphological characters in a lineage with C4 and C3-C4 intermediate species. - Bot. J. Linn. Soc. 169: 493-517
Sánchez-del Pino Y., Motley T.J. & Borsch T.
(See online at https://doi.org/10.1111/j.1095-8339.2012.01248.x) - 2015: A taxonomic backbone for the global synthesis of species diversity in the angiosperm order Caryophyllales - Willdenowia 45: 281 – 384
Hernández-Ledesma P., Berendsohn W. G., Borsch T., Mering S. von, Akhani H., Arias S., Castañeda- Noa I., Eggli U., Eriksson R., Flores-Olvera H., Fuentes-Bazán S., Kadereit G., Klak C., Korotkova N., Nyffeler R., Ocampo G., Ochoterena H., Oxelman B., Rabeler R. K., Sanchez A., Schlumpberger B. O. & Uotila P.
(See online at https://dx.doi.org/10.3372/wi.45.45.301) - 2015: Amaranthaceae. In: Jorgensen P.M., Beck S.G. (ed.), Catálogo de las plantas vasculares de Bolivia. – pp. 200-211 (Monogr. Syst. Bot. Missouri Bot. Gard.)
Borsch T., Ortuño T. & Nee M.
- 2015: An integrative and dynamic approach for monographing species-rich plant groups - building the global synthesis of the angiosperm order Caryophyllales. – Perspectives Pl. Ecol. Evol. Syst. 17: 284–300
Borsch T., Hernández-Ledesma P., Berendsohn W. G., Flores-Olvera H., Ochoterena H., Zuloaga F. O., von Mering S. & Kilian N.
(See online at https://doi.org/10.1016/j.ppees.2015.05.003) - 2016: Two new species of Iresine (Amaranthaceae: Gomphrenoideae) from Mexico supported by morphological and molecular characters. – Willdenowia 46: 165-174
Flores-Olvera H., Zumaya S., Borsch T.
(See online at https://doi.org/10.3372/wi.46.46113) - (2018) Evolutionary diversification of the African achyranthoid clade (Amaranthaceae) in the context of sterile flower evolution and epizoochory. – Annals of Botany 122 (1) 69–85
Di Vincenzo V., Grünstäudl M., Nauheimer L., Wondafrash M., Kamau P., Demissew S. & Borsch, T.
(See online at https://doi.org/10.1093/aob/mcy055)
