Seedless Vascular Plants

Origin of Vascular Plants

Oldest fossil dates back 425 mya

Several features show intermediate characteristics between bryophytes and vascular plants:

• Presence of independent, branching sporophytes

• Sporophytes did not always rely on gametophytes for nutrients

• Absence of true leaf, root or vascular tissues

Vascular Plant Characteristics

1. Presence of vascular tissue

2. Sporophyte dominates life cycle

3. Presence of true roots/leaves

Presence of Vascular Tissues

Vascular tissues develop exclusively in the sporophytes of vascular plants, and gametophytes lack vascular tissues

Functions:

Provides rigidity for vertical growth

Transports water/nutrients (via Xylem/Phloem)

Sporophytes Dominate Lifecycle

Sporophytes don’t rely on gametophytes for nutrients

Sporophytes are dominant in size, complexity and longevity, lead to angiosperms

Presence of Well Developed True Roots/Leaves

True Roots - Complex multicellular structures with internal, intercellular spaces

• Likely evolved from subterranean stems

• Anchors/Stabilizes vascular sporophytes

• Facilitates absorption/distribution of water and nutrients

True Leaves - Complex multicellular structures

• Increases surface area of sporophytes for photosynthesis

Microphylls/Megaphylls/Sporophylls

Microphylls - Small leaves with single veins, likely evolved as outgrowth of stems, common in lycophytes

Megaphylls - Large leaves with highly branched vascular systems

Sporophylls - Modified leaves with sporangia, two types:

Sori - Clusters of sporangia on undersides of sporophylls

Strobili - Cone structured formed by grouping of sporophylls

Homosporous and Heterosporous

Homosporous - plants have single type of spore that develops into bisexual gametophytes, seedless vascular plants are homosporous

Heterosporous - Plants have two types of spores:

Megaspores develop into female gametophytes

Microspores develop into male gametophytes

All seed plants and a few seedless vascular plants are heterosporous

Characteristic Common With Bryophytes

Presence of flagellated sperm

-Water is required for flagellated sperm to fertilize eggs in archegonia

-Seedless vascular plants are mostly found in moist habitats

Life Cycle of Vascular Plants

Haploid spore released → Spores germinate into gametophyte → Gametophyte matures into male/female (Antheridia and archegonia) → Diploid zygote formed from fertilization → Sporophyte developed from archegonium → Gametophyte dies, sporophyte becomes independent

Phylum Lycophyta

Club mosses, Spike mosses
Characteristics:
Presence of microphyll leaves

Presence of strobili containing sporangia

Reproduction via spores instead of seeds

Economic Significance:

Club mosses used as flash powder in photography

Phylum Monilophyta

Characteristics:

Presence of megaphyll leaves that grow via uncoiling

Sporangia often have spring-like structures that catapult spores

Most ferns are homosporous