The phenotypic diversity in African Salvia is associated with repeated introductions to the continent. Many important evolutionary processes, such as colonization, adaptation, parallelism and character transformation, are reflected in this comparatively small group. The data presented in this study can help to understand the evolution of Salvia sensu lato and other large genera.
Salvia L. in its traditional circumscription is the largest genus within the mint family. To date, the magnitude of the task has rendered it difficult to provide a genus-wide revision based on morphological data. Current molecular investigations based on a dense taxon sampling representing the whole phenotypic diversity and distribution range of Salvia confirmed that the genus is polyphyletic. Salvia species fall in 4 distinct clades, although all of them, except Clade IV, also include non-Salvia genera. A taxonomic revision is thus urgently needed with two different approaches that have to be considered: (1) to include the 5 morphologically distinct non-Salvia genera in Salvia or (2) to split Salvia s.l. into Salvia s.s. and several additional genera. Since Salvia is already highly heterogeneous in species distribution, morphology, and chromosome number, we prefer to split the genus into molecularly well-supported clades. This new concept may facilitate monographic studies and more focused analyses of character evolution within or between the clades. Species representing Salvia sect. Eremosphace Bunge (subclade III-A) were chosen exemplarily to provide arguments for elevating this particular group to the level of genus (Pleudia Raf.).
This study aims to identify the histological basis for the extraordinary, fast movement of the style in Marantaceae. Although this explosive pollination mechanism was subject of many studies, quantitative measurements to document volumetric changes have never been conducted. Based on physical parameters and limitations (poroelastic time), the movement itself is by far too fast to be explained by turgor changes solely. Therefore, we address the hypothesis that the style contains elastic structures to store energy allowing the fast movement. We provide an experimental approach in Goeppertia bachemiana to identify histological differences of styles in various states, i.e., steady, unreleased, and released state. Cross and longitudinal sections were used to reconstruct the cell volume in different sectors of the style. Histological data were discussed with respect to a putative water shift (turgor movement) and elastic instabilities that were proposed to explain the style movement of Marantaceae. Current data show, that the upper epidermis is under tensile stress in the unreleased state. After style release, the lower side of the style revealed an enormous water up-take. According to our results, we hypothesize that the fast style movement of G. bachemiana is likely based on an elastically stretched upper epidermis, whereas a “soaking tissue” at the lower side presumably mediates the up curling of the style. The experimental data show that at least for G. bachemiana, physical limitations such as the poroelastic time are suitable parameters to predict movements that are based on elastic instabilities.
Zusammenfassung
Pfeilwurzgewächse gehören zu den wenigen Beispielen für sehr schnelle pflanzliche Bewegungen. Diese kennt man unter anderem von fleischfressenden Pflanzen oder der Mimose. Das bekannteste Beispiel ist die Schließbewegung der Fangblätter von Venusfliegenfallen (Dionaea). Hier sind elektrische Impulse die Ursache für eine schnelle Reaktion auf den Reiz. Die Frage, wie das explosionsartige Einrollen des Griffels der tropischen Pfeilwurzgewächse zustande kommt, konnten bisherige Untersuchungen noch nicht zufriedenstellend beantworten. Elektrophysiologische Experimente helfen dabei, den Mechanismus hinter der Griffelbewegung besser zu verstehen.
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