The Two Phyla of Seedless Vascular: Pteridophytes

Lycophyta

and

Pterophyta

Traits of Seedless Vascular Plants

1. True lignified vascular system w/ xylem and phloem. True: roots, leaves, & stems.

2. Dominant sporophyte generation becomes independent of the parental gametophyte.

3.No Seeds! WHAT???!!

4. Adaptations inherited from bryophytes like anscestor: meristems, embryos, alt. of gen life cycle, walled resistant spores, gametangia, specialized epidermis, and secondary compounds.

* Traits 1 & 2 are shared by other vascular plants like angiosperms and gymnosperms.

Hypothesis for the evolution of leaves.

Microphylls, which have only one strand of vascular tissue anre thought to have evolved from a small stem outgrowth, where vascular tissue developed.

Megaphylls, support more photosynthetic activity then microphylls b/c of branced vascular system. Thought to be evolved through flattening and joining of multiple branches.

Homosporous

Heterosporous

                Microspore → Male Gametophyte → Sperm

                ↑

Sporophyte

                ↓

                 Megaspore → Female Gametophyte →  Egg

Sporophyll

modified leaves that bear sporangia

Sori

Clusters of sporangia, usually on the underside of Sporophylls

Strobili

Cones bearing sporangia, usually on the tips of shoots/branches.

Advantages of the Seed

• Multicellular embryo gets "headstart" at the germination stage
• Stored food for embryo allows for a head start and allows for extended dormancy.
• Multicellular, larger, and more complex than a spore=more resistant to harsh conditions.
• Larger and more complex= increased capacity to develop diversity adaptations.

Disadvantages of the Seed

• More energetically costly to produce

• To some extent, trade off quantity for quality.