<p>Seedless vascular plants continued Chapter 17</p><p>Phylum Pteridophyta  Majority of Pteridophyta are ferns  Most living ferns are homosporous  Two kinds of sporangia in ferns  Eusporangium  Large and contain many spores  Multicellular in origin  Leptosporangia  Arise from a single cell  Tapetum is two-cells-thick nutritive tissue  Annulus drying results in catapult-like discharge of spores</p><p>Pteridophyta  Eusporate ferns  Ophioglossales and Marattiales  Homosporous leptosporangiate ferns  Filicales  Heterosporous leptosporangiate ferns  Marsileales and Salviniales (water ferns)  Whisk ferns (Eusporate and rootless)  Psilotales</p><p>Order Ophioglossales  3 genera (Botrychium, Ophioglossum)  Each leaf has a vegetative portion or blade and a fertile segment  Gametophytes are subterranean, tuberous, elongate and have endophytic fungi  Gametophytes resemble those of Psilotales</p><p>Marattiales  Look more like “ferns”  Six living genera of 200 species</p><p>Filicales  Homosporous leptosporangiate  10,500 species  Fronds are megaphylls of sporophyte  Fronds are divided into pinnae along rachis  Fiddleheads – circinate vernation leaf development  Sporophyte is perennial stage in ferns Filicales  Sporangia occur in clusters called sori in many genera</p><p>Filicales  Young sori may be covered by specialized outgrowths of leaves called indusia</p><p>Filicales  Bisexual gametophyte is heart-shaped prothallus with rhizoids  Archegonia near notch in heart  Antheridia near rhizoids  Development timing deterimines inbreeding or outcrossing frequency</p><p>Filicales  Gametophyte is short-lived  In some Appalachian species, no sporophytes are formed  Produce gemmae</p><p>Water ferns  Heterosporous leptosporangiate ferns  Marsilcales and Salviniales</p><p>Water ferns  Sporocarps resist drying  Azolla contains cynanobacteria</p><p>Psilotales  Whisk ferns with two genera, Psilotum and Tmesipteris  Rootless and eusporangiate  Bisexual subterranean gametophyte with a symbiotic fungus</p><p>Equisitales  Genus Equisetum, horsetails  Jointed stems and rough textures  Homosporous  Sporangia are borne in groups of 5-10 along the margin of umbrella-like structures called sporangiophores, which are clustered into stroboli  Green, free-living gametophytes are bisexual or male</p>