Pericarp diversity in Cyperaceae tribe Scirpeae

Abstract

Transverse sections of the pericarp or fruit wall of 28 species and 30 taxa from all genera of family Cyperaceae tribe Scirpeae sensu Goetghebeur (1998) were investigated using SEM and X-ray analysis to study cell types and presence of different elements. Two genera described after my analyses were completed (Calliscirpus and Rhodoscirpus) are excluded from this investigation; also the genus Cypringlea described in 2003. Particular attention was paid to variation in cell types and presence of silicon and other elements in the different parts of the pericarp. This is a novel systematic method as previous investigations of elements in the pericarp have focused on the morphology of silicon phytoliths and not the actual occurrence of Si and other elements in the various cells. Four of seven investigated and accepted genera have silicon phytoliths, but Si is present in all genera and in 25 of 28 investigated species or in 27 of 30 taxa. Other elements were present in minor amounts. However, the pericarp of Trichophorum uniflorum (Trautv.) Malyschev & Lukitsch. from arctic Russia had no silicon, but a conspicuous Ca-plate in the epidermis cells. Plant species with a pericarp with a thick silicon layer are better adapted to endozoochorous seed dispersal by protecting the seed from digestive acids and the abrasive action of grinding in birds’ gizzards; also the mineral layer and/or a thick outer epidermis wall will protect against an intense UV radiation regime, such as the high Andes and the arctic. The new information discovered through X-ray analysis of the pericarp has the possibility to increase the reliability in analyses of fossil fruits of Cyperaceae. Fruit wall anatomy provides good characters for generic delimitations in some instances, and provides significant infrageneric variation in other genera. Of the seven investigated genera only Trichophorum and Phylloscirpus were heterogeneous as regards fruit characters.