Abstract Detail

Paleobotanical Section

Coiro, Mario [1], Mickle, James E. [2], Barone Lumaga, Maria Rosaria [3].

Epidermal morphology and the diversification of the cycads.

Recent analyses based on molecular data have revolutionized our understanding of cycad evolution and phylogeny. On the one hand, the traditional phylogeny based on morphology has been questioned. On the other hand, the use of molecular dating has suggested that most of the extant species diversity of the Cycadales originated during the Miocene-Pliocene, rejecting their status of “living fossils”.
However, many aspects of the morphology of the cycads remain poorly known. This complicates both the use of morphological characters in phylogenetic analyses and the evaluation of the cycad fossil record, which is particularly important for testing and updating the hypotheses emerging from molecular dating. Most of these analyses rely on a few fossils, some of which have been tentatively assigned to the stem group of modern genera on the basis of their macromorphology. However, many more fossils have been linked with modern genera or families, and some of these fossils would seem to strongly contradict the inference of molecular dating analyses. Particularly critical is the fossils record of cycadalean leaves. Since the classic studies on the cycadalean cuticles, very little new information has been added, leading to a very vague definition of the cycadalean stomata and of the characters needed to assign a leaf fossil to modern genera or families. We studied stomatal and cuticular micromorphology in 42 cycads species, integrating confocal and electron microscopy. The clarification of stomatal morphology allowed the recognition of definite structural constrains in stomatal structure in different cycads lineages. The comparison of extant cuticle and stomata structure with fossil forms contradicts the assignment of some fossil forms to modern genera, including some fossils traditionally used as calibration in molecular analysis. Likewise, the presence of contrasting leaf micromorphology characters in Cenozoic cycads suggests a more complex scenario for the history of cycad diversification.

1 - ETH Zuerich, Department Of Biology, Universitaetstrasse 2, Zuerich, Zurich, 8092, Switzerland
2 - North Carolina State University, Department of Plant and Microbial Biology, 2115 Gardner Hall, Box 7612, Raleigh, NC, 27695-7612, USA
3 - Università di Napoli Federico II, Dipartimento di Biologia, Orto Botanico, Via Foria, 223, Napoli, 80139, Italy

Keywords:
cuticle
cycads
fossils
leaf micromorphology
Phylogeny
stomata.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PPB001
Abstract ID:296
Candidate for Awards:None