What is a section in botany based upon?

Question

I am a bioinformatician working with plant data. Therefore my formation on plant biology and botany is "ok" but not very strong. When people talk about sections, I know that they talk about a phylogenetic rank that is lower than the genus but higher than the species. It groups subsets of species belonging to a genus together. What is the thing that puts them together? Morphology, origin, geography, metabolism, genome identity, ...?

Answer 1

My knowledge of Bioinformatics is good but dated and my Plant knowledge is good esp on the Cereals

But I have rarely if ever heard of 'section' almost certain it was never part of the Linnean taxonomy.