Seedless Vascular Plants and Early Forests

What innovation allowed plants to grow taller and colonize new habitats?

The evolution of vascular tissue (xylem and phloem).

What do vascular plants have that bryophytes do not?

True roots, stems, and leaves.

What are the two main types of vascular tissue?

Xylem and phloem.

What does xylem do?

Transports water and minerals from roots to the rest of the plant.

What does phloem do?

Distributes sugars, amino acids, and organic products throughout the plant.

What provides structural support in vascular plants?

Lignin, a polymer that strengthens xylem cell walls.

What is the dominant generation in vascular plants?

The sporophyte (diploid) generation.

How do seedless vascular plants reproduce?

Through flagellated sperm that require water to reach the egg.

What are the two major groups of seedless vascular plants?

Lycophytes (club mosses, spike mosses, quillworts) and Monilophytes (ferns, horsetails, whisk ferns).

What is the function of roots?

To anchor the plant and absorb water and nutrients from the soil.

What are microphylls?

Small leaves with a single, unbranched vein — found in lycophytes.

What are megaphylls?

Larger leaves with highly branched vascular veins — found in ferns and seed plants.

What are sporophylls?

Modified leaves that bear sporangia (spore-producing structures).

What are strobili?

Cone-like structures formed by groups of sporophylls (seen in lycophytes and some ferns).

What does the mature fern sporophyte produce?

Sporangia on the underside of fronds.

What are sori?

Clusters of sporangia on fern leaves (fronds).

What do fern sporocytes produce by meiosis?

Haploid spores.

What do fern spores grow into?

Gametophytes — small, heart-shaped, photosynthetic plants.

Where are the archegonia and antheridia found on the fern gametophyte?

On the underside of the gametophyte.

How does fertilization occur in ferns?

Sperm swim through water to fertilize eggs.

What grows from the fertilized egg (zygote)?

A new diploid sporophyte, the dominant fern generation.

When did seedless vascular plants dominate Earth?

During the Carboniferous period (~359–299 million years ago).

What did ancient vascular plants form during the Carboniferous?

Vast swamp forests of giant ferns, horsetails, and lycophytes.

What important resource formed from these forests?

Coal, created from compressed plant material over millions of years.

How did Carboniferous forests affect global CO₂ levels?

They reduced atmospheric CO₂, contributing to global cooling.

Why did seedless vascular plants decline?

Due to drier climates and the rise of seed plants better adapted to land.