Morphology Tool

Although Brassicaceae are morphologically well-defined and easily distinguishable from any other angiosperm family by their general and little variable flower architecture (almost always 4 sepals, 4 petals, 4+2 stamens, 2 fused carpels) and fruit characteristics (siliques or silicles, which can be also compressed in two different ways), infra-familiar grouping based on morphological characters often failed on higher taxonomic levels such as tribes and often even on a genus level. In the past this situation often resulted in a circumscription of paraphyletic taxa.

As a consequence, there is no “backbone set” of characters to be selected a-priori and to be studied across the entire family. Traditionally, in Brassicaceae characters have been elaborated on to describe, characterize and determine morphological variation on species and genus level, but not to compare systematically between genera or other higher order taxonomic units.

Furthermore, any taxonomical concept from the past and preceding molecular systematics (e.g., Janchen, 1942; Hayek, 1911; Schulz, 1936) until the late 1990th turned out to be highly artificial and very often did not define monophyletic groups correctly (Koch et al., 2003). But this also implies that past concepts scoring different characters are not biased a-priori by a phylogenetically-constraint character selection.

The given phylogenetic framework is based on a robust and significant “maternal perspective” (Hohmann et al., 2015; Guo et al., 2017), however, it should be noted that there is some conflictual signal compared to phylogenetic analysis based on nuclear genes (e.g., Huang et al., 2016), with its evolutionary-biological meaning not solved yet.

Characters and their states have been scored in the past very carefully and in particular on genus level. They comprise a comprehensive character set reflecting our awareness of variable character among Brassicaceae species and genera. However, characters often used numerous character states (up to 17) or combined characters from stem, leaves, flowers and fruits. Therefore, it is not recommended to use the raw data for respective evolutionary analysis.

Therefore, we developed a new morphological data matrix with reduced complexity of coded characters and their states in a more applicable manner to study characters and their evolution, which will be released here soon.

• Guo X, Liu J, Hao G, Zhang L, Mao K, Wang X, Zhang D, Ma T, Hu Q, Al-Shehbaz IA, Koch MA. 2017. Plastome phylogeny and early diversification of Brassicaceae. BMC Genomics 18(1): e176. DOI: 10.1186/s12864-017-3555-3
• Hayek A. 1911. Entwurf eines Cruciferen-Systems auf phylogenetischer Grundlage. Beih. Bot. Centralbl. 27: 127–335.
• Hohmann N, Wolf EM, Lysak MA, Koch MA. 2015. A time-calibrated road map of Brassicaceae species radiation and evolutionary history. Plant Cell 27(10): 2270–2284. DOI: 10.1105/tpc.15.00482.
• Huang CH, Sun R, Hu Y, Zeng L, Zhang N, Cai L, Zhang Q, Koch MA, Al-Shehbaz I, Edger PP, Pires JC, Tan DY, Zhong Y, Ma H. 2016. Resolution of Brassicaceae phylogeny using nuclear genes uncovers nested radiations and supports convergent morphological evolution. Mol. Biol. Evol. 33(2): 394–412. DOI: 10.1093/molbev/msv226.
• Janchen E. 1942. Das System der Cruciferen. Österr. Bot. Z. 91: 1–28.
• Koch M, Mummenhoff K, Al-Shehbaz IA. 2003. Molecular systematics, evolution, and population biology in the mustard family (Brassicaceae): A review of a decade of studies. Ann. Missouri Bot. Gard. 90(2): 151–171.
• Schulz OE. 1936. Cruciferae. In: Engler A, Harms H. (Eds.) Die natürlichen Pflanzenfamilien. Ed. 2, vol. 17b. Englemann, Leipzig, Pp. 227–658.