Reconstructions of Selected Seed Ferns

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Abstract
Seed ferns (pteridosperms) make up a heterogeneous group of broadleaf gymnosperms. Our attempts to reconstruct these extinct plants here summarize research over many years on the best-known seed ferns. We have named each reconstructed plant after its best-preserved ovulate fructifications, because these are the most reliable parts for identification of seed plants. We envisage Early Carboniferous (about 352 million years ago) Stamnostoma huttonense as a large tree, foresting elevated terraces and other well-drained areas of coastal plains. Swampy lagoon margins of the same coast probably were wooded with lycopods and small shrubby seed ferns such as Lyrasperma scotica. Of comparable age, but on well-drained ashy soils flanking inland volcanoes, was the early successional Calathospermum fimbriatum. Unlike these other plants, which were probably pollinated and dipersed by wind and water, arthropods may have played a role in the reproduction of C. fimbriatum. Earliest Late Carboniferous (about 320 million years old) Lagenostoma lomaxii is reconstructed as a bushy understory shrub in swamps of arborescent lycopods. Latest Late Carboniferous (about 296 million years old) Pachytesta illinoensis was a tree probably growing on elevated and nutrient-rich areas in and around permanently waterlogged swamps of marattiaceous tree ferns. Pachytesta illinoensis had large prepollen probably dispersed by insects. Its fleshy ovules may have been dispersed by large amphibians, reptiles, or fish. Another seed fern of these latest Carboniferous swamps, Callospermarion pusillum, is reconstructed as an early successional scrambling vine. Its pollen probably was dispersed by wind, and its numerous small seeds scattered widely by wind and water. In contrast to these Euramerican plants of tropical and subtropical climates, Late Permian (about 245 to 253 million years old) Dictyopteridium sporiferum was a dominant tree of cool temperate swamp woodlands of intermontane valleys in the southern hemisphere. Large air chambers in its roots enabled it to grow in waterlogged soils. Woodlands of southern hemisphere mid-continental lowlands during Late Triassic time (225 to 230 million years ago) included abundant trees of Umkomasia granulata, and a shrubby understory including Peltaspermum thomasii. Middle Jurassic (175 to 183 million years old) Caytonia nathorstii is reconstructed as a tree of lowland mixed conifer-broadleaf forest in a subtropical, seasonally wet paleoclimate. Its ovules were enclosed in berrylike cupules, which may have been pollinated and dispersed by small animals. From these examples, it is apparent that seed ferns were exceptionally diverse broadleaf plants which occupied a variety of niches now occupied by angiosperms.

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