Chapter 29 Plant Diversity I

Charophytes

The group of green algae most closely related to land plants; share rosette cellulose complexes, similar peroxisome enzymes, and chloroplast genes with plants

Embryophytes

Another name for land plants; defined by the retention of a multicellular embryo within maternal gametophyte tissue

Cuticle

Waxy, waterproof layer secreted by epidermal cells; prevents desiccation in aerial plant parts

Stomata

Pores in the leaf epidermis flanked by guard cells; regulate CO₂ uptake and water vapor loss (transpiration)

Lignin

Tough phenolic polymer in secondary cell walls of vascular tissue; provides structural support against gravity and waterproofs xylem

Sporopollenin

Chemically inert polymer in spore and pollen walls; protects against UV radiation, desiccation, and decay; enables aerial dispersal

Apical meristems

Regions of actively dividing cells at root and shoot tips; enable indeterminate primary growth (length)

Alternation of generations

Life cycle with alternating multicellular haploid (gametophyte) and diploid (sporophyte) stages; unique to land plants among organisms

Gametophyte

The haploid (n) multicellular generation in plant life cycles; produces gametes by mitosis

Sporophyte

The diploid (2n) multicellular generation in plant life cycles; produces spores by meiosis

Archegonium

Flask-shaped female gametangium producing one egg; found in nonvascular plants and seedless vascular plants

Antheridium

Male gametangium producing flagellated sperm; found in nonvascular plants and some vascular plants

Bryophytes

Nonvascular land plants (mosses, liverworts, hornworts); gametophyte-dominant; need liquid water for fertilization

Phylum Bryophyta

Mosses; the most diverse bryophyte group; includes Sphagnum (peat moss)

Sphagnum

Peat moss; forms bogs; stores ~30% of all terrestrial carbon; acidic and antiseptic; absorbs 20× its weight in water

Phylum Hepatophyta

Liverworts; simplest land plants; flat thallus; reproduce vegetatively via gemma cups

Phylum Anthocerophyta

Hornworts; horn-shaped sporophytes; unique: sporophyte has stomata and photosynthesizes; harbor N-fixing cyanobacteria

Vascular plants (tracheophytes)

Plants with lignin-reinforced xylem and phloem; sporophyte dominant; ~420 mya origin

Lycophytes

Phylum Lycophyta; oldest surviving vascular plant lineage; have microphylls; include club mosses, spike mosses, quillworts

Microphylls

Small leaves with a single unbranched vein; found in lycophytes; evolved from stem enations

Monilophytes

Ferns, horsetails, and whisk ferns; seedless vascular plants; sister group to seed plants

Megaphylls

Leaves with complex branching vein systems; found in ferns and seed plants; evolved from a webbed branch system

Sori

Clusters of sporangia on the undersides of fern fronds; produce haploid spores by meiosis

Prothallus

The tiny, heart-shaped, free-living gametophyte of ferns; produces archegonia and antheridia

Heterospory

Producing two types of spores: microspores (→ male gametophytes) and megaspores (→ female gametophytes); found in seed plants and some lycophytes