A century of seed ferns: A symposium to celebrate paradigm shifts in the understanding of seed plant
Galtier, Jean .
Arborescent seed ferns of the Pitus type.
The earliest (Devonian) cupulate seed plants were characterized by their small stature and slender protostelic stems (less than 10 mm in diameter) bearing highly divided fronds. The seed ferns recorded during the following 12 millions years (i.e. Tournaisian time) are represented by a large number of detached seeds or cupulate structures and by more than 40 taxa corresponding to different types of anatomically preserved stems. The latter document an impressive diversification of the vegetative morphology and habit with at least two classes of size. A majority of these early (calamopityalean, buteoxylalean and lyginopteridalean) seed ferns are interpreted as r-selected (scrambling to lianescent) plants showing relatively small stems (generally less than 5 cm diameter), small primary vascular system, manoxylic secondary xylem but large fronds and sometimes long internodes. In contrast, some arborescent plants with large trunks, corresponded to k-selected trees showing a thick development of generally dense wood, a broad eustele consisting of a large number of discrete primary xylem strands, short internodes and medium-sized fronds. New data have been obtained on Pitus, the best known member of this group, and as well on Eristophyton, Bilignea, Stanwoodia. However emphasis is placed on the reinvestigation of Aporoxylon from Germany and on the description of new taxa from the Tournaisian of France and Algeria which all exhibit broad circular parenchymatous pith with over 40 sympodial xylem strands and dense secondary xylem but differing in leaf trace features. Of particular interest, one new plant from France shows leaf traces, double in origin, and a petiole base of the Kalymma-type, therefore showing characteristics of calamopityalean seed ferns but being quite distinct in features of the stele, secondary xylem and phloem. The problem of the origin and significance of these arborescent forms in seed plants phylogeny is discussed.
1 - CIRAD, UMR5120, Botanique & Bioinformatique, TA40/ PS2, Bouleverd de la Lironde, Montpellier, 34398, France
Presentation Type: Symposium
Location: Ballroom 1 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 8:15 AM