Trimerophytopsida

Trimerophytopsida is an extinct group of early vascular plants known from the Silurian and Devonian periods. Its members had branching stems and are regarded as close to the ancestry of ferns and seed plants.

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Vascular plant: A plant with specialized tissues that transport water, minerals, and sugars through its body. Trimerophytes belonged to the early diversification of plants with internal transport tissues.
Pseudomonopodial branching: A branching pattern in which one axis continues growth while lateral branches remain subordinate. Unequal branching helped produce the upright axes characteristic of several trimerophytes.
Trimerophyton: An extinct genus of Devonian plants with branching axes and terminal sporangia. It is the genus that gives Trimerophytopsida its name.
Silurian: A geologic period spanning about 444 to 419 million years ago. The earliest vascular-plant history leading toward trimerophytes began in this period.
Xylem: Plant tissue that conducts water and minerals and often provides structural support. Its conducting strands are among the key features preserved in trimerophyte fossils.
Telome theory: A theory that explains the evolution of complex plant organs from branching systems of terminal axes. It interprets the branching architecture from which later leaves and reproductive structures may have evolved.
Psilophyton: An extinct genus of early Devonian vascular plants with branching stems and spore-bearing structures. Its fossils document the characteristic architecture associated with trimerophytes.
Devonian: A geologic period spanning about 419 to 359 million years ago, marked by major diversification of land plants. Most well-known trimerophyte fossils come from this period.
Tracheid: An elongated water-conducting cell in vascular plants, strengthened by lignified walls. Tracheids formed the water-conducting tissue in these early vascular plants.
Sporangium: A structure in which spores are produced and released. Trimerophytes bore sporangia at the ends of branches rather than in flowers or cones.