Molecular data reveal convergence in fruit characters used in the classification of Thlaspi s. l. (Brassicaceae)

Abstract

Phylogenetic relationships of 18 Thlaspi s.l. species were inferred from nuclear ribosomal internal transcribed spacer (ITS) sequence data. These species represent all sections of the basic classification system of Schulz primarily based on fruit characters. The molecular phylogeny supported six clades that are largely congruent with species groups recognized by Meyer on the basis of differences in seed coat anatomy, i.e. Thlaspi s.s., Thlaspiceras, Noccaea (Raparia included), Microthlaspi, Vania and Neurotropis. Some of these lineages include species which are morphologically diverse in fruit shape (e.g. Thlaspi s.s.: T. arvense - fruits broadly winged, T. ceratocarpum - fruits with prominent horns at apex, T. alliaceum - fruits very narrowly winged). Furthermore, the same fruit shape type is distributed among different clades. For instance, fruits with prominent horns at apex are found in Thlaspi s.s. (T. ceratocarpum) and Thlaspiceras (T. oxyceras). These results clearly indicate convergence in fruit characters previously used for sectional classification in Thlaspi s.l. (C) 1997 The Linnean Society of London.