Major Plant Phyla

Why This Matters

When you study plant phyla, you're really learning the story of how plants conquered land—and the evolutionary innovations that made it possible. Each phylum represents a different solution to the same fundamental challenges: how to transport water and nutrients, how to reproduce without swimming sperm, and how to protect developing embryos. Your exams will test whether you understand these adaptations as a progression, not just a list of names.

The key concepts you'll be tested on include vascular tissue evolution, the shift from gametophyte to sporophyte dominance, spore vs. seed reproduction, and the emergence of flowers and fruit. Don't just memorize which plants have what—know why each innovation matters and what problem it solved. That's what separates a 5 from a 3.

---

Non-Vascular Plants: The Bryophytes

These ancient lineages never evolved true vascular tissue, which limits their size and confines them to moist habitats. Without xylem and phloem, water and nutrients move by diffusion and osmosis alone. All three bryophyte phyla share gametophyte dominance—the green, photosynthetic plant you see is the haploid generation.

Bryophyta (Mosses)

• Gametophyte-dominant life cycle—the familiar green cushion is haploid; the sporophyte is a dependent stalk and capsule
• No true roots, stems, or leaves—instead possess rhizoids, and leaf-like structures that lack vascular tissue
• Ecological pioneers in soil formation and erosion control, often first colonizers of bare rock

Marchantiophyta (Liverworts)

• Two distinct body forms—thallose (flat, ribbon-like) or leafy (with leaf-like lobes arranged in rows)
• Asexual reproduction via gemmae—small cups on the thallus surface contain clonal propagules
• Indicator species for moist, unpolluted habitats; highly sensitive to environmental changes

Anthocerotophyta (Hornworts)

• Horn-shaped sporophytes—unique elongated structures that continue growing from a basal meristem
• Symbiosis with cyanobacteria—harbor nitrogen-fixing Nostoc in mucilage cavities, adding nitrogen to ecosystems
• Single large chloroplast per cell—unusual feature shared with algae, suggesting ancient lineage

---

Seedless Vascular Plants: The Pteridophytes

The evolution of vascular tissue was a game-changer—xylem and phloem allowed plants to grow tall and colonize drier habitats. However, pteridophytes still require water for fertilization because their sperm must swim to eggs. This group shows sporophyte dominance for the first time.

Pteridophyta (Ferns and Fern Allies)

• Vascular but seedless—possess true roots, stems, and fronds with xylem and phloem, but reproduce via spores
• Alternation of generations with free-living gametophyte—the heart-shaped prothallus is independent but short-lived
• Diverse growth forms—range from tiny aquatic ferns (Azolla) to 15-meter tree ferns in tropical forests

---

Gymnosperms: Naked Seed Plants

Gymnosperms solved the water-dependency problem with pollen and seeds—no more swimming sperm. Seeds provide protection and nutrition for the embryo, enabling colonization of drier environments. The term "gymnosperm" means "naked seed" because seeds aren't enclosed in fruit.

Pinophyta (Conifers)

• Cone-bearing reproduction—pollen cones (male) release wind-dispersed pollen; seed cones (female) protect developing seeds
• Needle-like or scale-like leaves—thick cuticle and sunken stomata reduce water loss in cold or dry climates
• Dominant forest trees in boreal and montane ecosystems; major source of timber, paper pulp, and resins

Cycadophyta (Cycads)

• Palm-like appearance but gymnosperm anatomy—stout trunk with crown of large compound leaves; produce cones, not flowers
• Dioecious reproduction—individual plants are either male or female, with some of the largest cones in the plant kingdom
• Living fossils from the Mesozoic; once dominant, now restricted to tropical and subtropical regions

Ginkgophyta (Ginkgo)

• Single surviving species—Ginkgo biloba is the only living member; all others known only from fossils
• Distinctive fan-shaped leaves—deciduous, with dichotomous venation pattern unique among seed plants
• Fleshy seed coat—technically not a fruit; produces foul-smelling butyric acid when mature (only on female trees)

Gnetophyta (Gnetophytes)

• Three bizarre genera—Ephedra (desert shrubs), Gnetum (tropical vines/trees), Welwitschia (two-leaved desert oddity)
• Angiosperm-like features—vessel elements in xylem and double fertilization in some species suggest convergent evolution
• Extreme habitat specialists—adapted to deserts and tropics with unique water-conservation strategies

---

Angiosperms: Flowering Plants

Angiosperms are the evolutionary superstars—flowers attract pollinators for efficient reproduction, and fruits protect and disperse seeds. Double fertilization produces both embryo and endosperm (nutritive tissue), giving seedlings a head start. This phylum contains over 300,000 species.

Magnoliophyta (Flowering Plants)

• Flowers and enclosed seeds—ovules protected within carpels; mature ovary becomes fruit
• Double fertilization—one sperm fertilizes egg (embryo), another fuses with polar nuclei (endosperm)
• Ecological and economic dominance—includes nearly all crop plants, hardwood trees, grasses, and wildflowers

---

Quick Reference Table

---

Self-Check Questions

1. Which two phyla share gametophyte dominance AND spore reproduction, but differ in whether they have vascular tissue?

2. A plant produces cones, has needle-like leaves, and thrives in cold climates. Which phylum does it belong to, and what makes it a gymnosperm rather than an angiosperm?

3. Compare and contrast ferns and mosses in terms of their vascular tissue, dominant generation, and habitat requirements.

4. If an FRQ asks you to trace the evolution of reproductive strategies in land plants, which four key innovations should you discuss, and which phyla best illustrate each?

5. Welwitschia, Ephedra, and Gnetum all belong to the same phylum despite looking completely different. What shared characteristics unite them, and why are they considered "intermediate" between gymnosperms and angiosperms?