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Noun1.progymnosperm - an ancestral fossil type from which modern gymnosperms are thought to have derived
gymnosperm - plants of the class Gymnospermae having seeds not enclosed in an ovary
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These were characterised by cosmopolitan plant genera such as the progymnosperm tree Archaeopteris, which has also been described from Waterloo Farm (Anderson et al.
These include 13 extant homosporous filicaleans, 17 extinct homosporous and heterosporous ferns from Paleozoic strata, five extant and one extinct heterosporous leptosporangiate ferns, two extant marattiaceous ferns, two extant ophioglossaceous ferns, one extant and two extinct equisetophytes, both extant homosporous psilotophytes (i.e., Psilotum and Tmesipteris), one extinct heterosporous progymnosperm, three extinct and one extant seed plants, and the extinct homosporous trimerophyte Psilophyton crenulatum (Appendix 1).
These progymnosperms eventually gave rise to plants with leaves and seeds.