Microspore wall organisation and ultrastructure in two species of Selaginella (Lycophyta) producing permanent tetrads

Spore morphology and ultrastructural features of the permanent microspore tetrads of Selaginella convoluta and S. lepidophylla were studied with light microscopy, scanning and transmission electron microscopy. The four members of each tetrad in S. convoluta are linked together through a common envelope and form an unbroken complex system of alveoli that connects the equatorial and distal regions of the microspores. In the proximal exospore of microspores, no differentiation referable to an apertural fold was observed but an interruption of the exospore is evident in that area in germinating microspores. The distal exospore is composed of three strata: inner zone, intermediate zone and outer alveolar. In S. lepidophylla tetrads, the four microspores are assembled within a common tetrad envelope and are equatorially connected by a prominent ridge. The distal regions of the microspores are free. In the proximal exospore of microspores, no differentiation referable to an apertural fold was observed. The tetrad envelope appears as a wide common coat, which, on the surface and depending on the regions, is granular or alveolate, centrally perforated and, in section, consists of a single layer or forms a two-layered, more or less intricate, network. This envelope has the same contrast as the exospore outer layer and shows, in its median zone, cavities with opaque contents, quite similar to those of the microspore exospore layer. These two different types of tetrads emphasise the outstanding structural diversity of the microspore sporoderm in living Selaginellaceae.Fil: Morbelli, Marta Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lugardon, Bernard. Université Paul Sabatier; Franci

The Triassic Lycopsids Pleuromeia and Annalepis: Relationships, Evolution, and Origin

Volume: 91Start Page: 115End Page: 14

Spores of the Pteridophyta

Volume: 81Start Page: 108End Page: 10

Morphology and wall ultrastructure of the megaspore Lagenicula (Triletes) variabilis (Winslow, 1962) Arioli et al. (2004) from the Lower Carboniferous of Ohio, USA

International audienceMegaspores assigned to Lagenicula (Triletes) variabilis (Winslow, M., 1962. Plant spores and other microfossils from Upper Devonian and Lower Mississippian Rocks of Ohio. Geol. Surv. Prof. Pap. 364, 1-93) Arioli et al., 2004, from the Lower Carboniferous (Tournaisian) of northeastern Ohio, USA, have been analysed using light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These studies provide new information on morphology, gross structure and wall ultrastructure. Previous reports of in situ megaspores indicate that Upper Carboniferous Lagenicula (and related forms) derive from the Lepidocarpaceae, that include many of the large arborescent lycopsida that dominated the Euramerican Coal Measure forests. Based on morphological and, to a lesser extent, ultrastructural similarities with Upper Carboniferous forms, it seems likely that Lower Carboniferous Lagenicula also derive from similar plants. This suggests that large arborescent lycopsids typical of the Upper Carboniferous (or at least their precursors) were already present in the Lower Carboniferous, possibly forming forests in similar environments. These may be underrepresented in the fossil record because of the paucity of deposits of this age representing such environments