'False resupination' in the flower-pairs of Thalia (Marantaceae)

Resupination, i.e., the turn by 180 degrees, arranges zygomorphic flowers in a suitable position for pollination. It is well-known from orchids, but also occurs in further angiosperm families. Within the genus Thalia L. (Marantaceae), T. dealbata has erect and T. geniculata pendulous inflorescences. Nevertheless, in both species the zygomorphic flower-pairs show the right position for pollination. Thus, resupination is expected in Marantaceae. To reconstruct spatial arrangement, flower development was investigated from meristem formation to anthesis. Early morphogenetic stages were analysed under the scanning electron microscope, late stages were documented by time-lapse records. Gravity experiments were added to test for plastic or genetically fixed flower-pair position. Flowers in both Thalia species develop almost identically. They originate from a common primordium and show the unusual floral organ sequence already described for the family. In T. dealbata, the flower-pair gets its final position by bending 90 degrees backwards, while in T. geniculata a lateral rotation of 90 degrees takes place shortly before anthesis. In both species, position is genetically fixed. Results clearly indicate that the flower-pairs in Thalia do not show resupination according to the given definition. Instead of the expected 180 degrees turn in one species, flower-pairs in both species each dislocate for 90 degrees. (C) 2015 Elsevier GmbH. All rights reserved.