Gymnosperms Ancestor II

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6 Terms

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Gymnosperms

Evolved at the end of Devonian (410-360 mya)

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Pteridosperms

1st seed plants, evolved from fern-like plants from ancestors that where heteresporous. Small mobile spores containing male gamete (pollen) and large female spores retained on parent plant and containing female gamete (ovule).

Seed ferns diversified early in their evolution many different types with seed condition. Common tree fern (cyathea dregei).

At some stage almost all gymnosperm groups proposed as possible angiosperm ancestors. But mostly likely are pine-line and glossopterid-line.

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Pine line

Predominantly ovules not enclosed in cupules (leaves/bracts that enclose the ovules, evolved to protect ovules). Ovules on leaves/bracts. Angiosperms originated from here = both outer integument and carpel in angiosperms derived from leaves/bracts to enclose ovule. (Cycads. Ginkgos.Cordiates. Voltziales. Pines. Gnetophytes).

1. Coniferophyta. Pinales: include all conifers I.e cedar, pine, redwood, cypress

  1. Cycadophyta: mostly (sub)tropical. c.100 species. Male and female cones. Hirtculture. Palmlike evergreen leaves.

  2. Ginkgophyta: single species (ginko biloba). Dioecious- sexes on seperate plants.

  3. Gnetophyta: 3 genera. 76 species.

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Pine cone

Megaspore is retained within megasporangium.

Megasporophyll tissue (integument) envelopes megasporangium.

Entrance for microspore= micropyle.

Ovule= megaspore, megasporangium, integuments.

Female cones (megasporophylls), has 2 ovules and male cones (microsporophylls)

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Glossopterid line

Predominantly ovules enclosed in cupules (leaves/bracts that enclose the ovules for protection). Ovule is within cupules. Angiosperms evolved from this line= cupule becomes outer integument and leaf becomes carpel. Glossopterids. Gigantopteris. Caytonia. Pentoxylon. Bennettitales (flowers have bracts. Pollen producing organ. Cupules clusters on inside).

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Angiosperm ancestor

Also depends on whether the angiosperm flower evolved from a : single unbranded stem (euanthial theory) or compound branched stem (pseudanthial theory).