Abstract Detail

Novel Approaches to Plant Evolution from Paleontological, Physiological, and Developmental Perspectives

Decombeix, Anne-Laure [1], Momont, Nicolas [2], Meyer-Berthaud, Brigitte [1].

Evolution of secondary xylem and phloem based on the Paleozoic fossil record.

The appearance of a cambium producing secondary vascular tissues is one of the key innovations that occurred among vascular plants during the Devonian (-420 to 360 My). The fossil record indicates that a unifacial cambium producing secondary xylem has evolved multiple times during the Paleozoic. On the other hand, the bifacial cambium producing both secondary xylem and secondary phloem that is still found in extant plants is thought to have evolved only once*. It characterizes the lignophytes, the clade comprising the progymnosperms (Devonian-Carboniferous) and the seed plants (Devonian-present). In this talk we will review the current state of our knowledge on the evolution of secondary xylem and secondary phloem in lignophytes during the Paleozoic. Fossil wood is one of the most common types of plant fossils and there are countless examples of informative Paleozoic specimens. Secondary phloem on the other hand is often degraded or lost (decortication) before fossilization; it is however relatively well preserved in some representative Paleozoic taxa. We will see how the study of these fossils is essential to obtain a more accurate picture of secondary xylem and phloem evolution. Three major points will be addressed: (1) The organization of secondary xylem and secondary phloem in the oldest representatives of the lignophytes, the aneurophytalean progymnosperms of the Devonian, and how it compares to inferences on the ancestral organization of these tissues that are based solely on extant plants; (2) Secondary xylem and phloem anatomy in other Devonian lignophytes: the archaeopteridalean progymnosperms (the first lignophytes to develop the tree habit) and the first seed plants. We will also look into the secondary xylem anatomy of the Devonian Stenokoleales, a group considered by some authors as closely related to the seed plants but in which the presence of a bifacial cambium has not been demonstrated; (3) The diversification of secondary xylem and secondary phloem organization from the Early Carboniferous on, and how it likely reflects the diversification of growth habit and habitats of the seed plants. Some of these Early Carboniferous taxa presented combinations of characters not seen in extant gymnosperms. We will discuss how this fits within evolutionary trends based on the study of extant taxa and we will present future directions for this research. *with the possible exception of Sphenophyllum.

1 - CNRS, UMR AMAP, C/o CIRAD, TA A51/PS2, Bvd De La Lironde, Montpellier, F-34398, France
2 - Université de Liège, Paléobiogéologie, Paléobotanique et Paléopalynologie, Département de Géologie, B18, , Sart Tilman, Liège, Belgium
3 - CNRS, UMR AMAP, C/o CIRAD, TA A51/PS2, Bvd De La Lironde, Montpellier, F-34398, France

Keywords:
xylem
phloem
cambium
lignophytes
evolution.

Presentation Type: Symposium Presentation
Session: SY11, Novel approaches to plant evolution from paleontological, physiological, and developmental perspectives
Location: 101/Savannah International Trade and Convention Center
Date: Wednesday, August 3rd, 2016
Time: 1:45 PM
Number: SY11002
Abstract ID:76
Candidate for Awards:None