Progymnosperm

Progymnosperms were extinct woody plants that reproduced by spores rather than seeds. They combined secondary wood growth like that of gymnosperms with reproductive structures resembling those of ferns.

Vascular plant: A plant with specialized tissues that transport water, minerals, and sugars through its body. Progymnosperms had vascular tissues that supported large, woody growth.
Lignin: A complex polymer deposited in plant cell walls that strengthens and waterproofs vascular tissues. Lignified tissues helped progymnosperms build sturdy trunks and branches.
Devonian: A geological period lasting from about 419 to 359 million years ago, marked by major diversification of land plants. Many of the best-known progymnosperms lived during this period.
Archaeopteris forest: A Late Devonian forest dominated by large trees of the progymnosperm genus Archaeopteris. These forests demonstrate the scale of landscapes built by spore-producing woody plants.
Secondary growth: An increase in a plant stem or root's thickness produced by lateral meristems. This growth produced the substantial wood characteristic of progymnosperms.
Cambium: A layer of dividing plant cells that produces secondary vascular tissues. A vascular cambium generated the secondary wood of many progymnosperms.
Middle Devonian: The interval from about 393 to 383 million years ago within the Devonian Period. Early progymnosperms appear in the fossil record during this interval.
Forest: A land ecosystem dominated by trees or other woody vegetation. Progymnosperms helped establish some of the earliest extensive tree-dominated ecosystems.
Xylem: Vascular tissue that conducts water and minerals and often provides structural support. Progymnosperm wood consisted largely of secondary xylem.
Heterospory: The production of two distinct spore types, typically associated with male and female gametophytes. Some progymnosperms produced distinct spore types, a reproductive pattern relevant to seed evolution.

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