Tracheophytes Flashcards
Ferns and other seedless vascular plants were the first plants to grow tall\
*Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution
*Vascular plants began to diversify during the Devonian and Carboniferous periods
*Vascular tissue allowed these plants to grow tall
*Seedless vascular plants have flagellated sperm and are usually restricted to moist environment
Lycophyte gametophyte
*Highly reduced, lives in soil
*Photosynthetic or non-photosynthetic
*Sporophyte initially parasitic
lycophyte sporophyte
microphyllous: – small leaf with single vascular trace
*Sporangia in strobil
Homosporous or heterosporous
fern sporophyte
megaphyllous: – large leaf with complex vasculature
*Sporangia on the undersides of the leaves typically in sori
Generally homosporous
Ferns and lycophytes require moisture because:
*Gametophyte : small size + lack of roots at risk of desiccation
*Gamete exchange requires water (gametophytes free-living, sperm flagellate)
*Spores lack storage reserves , and dormancy limited
Classification of Seedless Vascular Plants
*There are two phyla of seedless vascular plants:
–Phylum Lycophyta includes club mosses, spike mosses, and quillworts
–Phylum Pterophyta includes ferns, horsetails, and whisk ferns and their relatives
Living vascular plants are characterized by:
*Life cycles with dominant sporophytes
*The gametophytes are tiny plants that grow on/below the soil surface or inside spore walls (seed plants)
*Vascular tissues called xylem and phloem
*Well-developed roots and leaves
Tracheophyte sporophyte function
*roots
anchorage
water & nutrient uptake
*stem with lignified conducting tissues
water, solute and photosynthate transport
supports leaves and reproductive structure
Transport in Xylem and Phloem
*Vascular plants have two types of vascular tissue: xylem and phloem
*Xylem conducts most of the water and minerals and includes dead cells called tracheids
*Phloem consists of living cells and distributes sugars, amino acids, and other organic products
*Water-conducting cells are strengthened by lignin and provide structural support
*Increased height was an evolutionary advantage
Xylem tracheids
*Pipelike, with tapering ends
*Non-living at maturity
*Cell walls secondarily thickened – impregnated with lignin
*Connected by bordered pits
*Role = water transport
Phloem sieve cells
*Elongated, with porous connections
*Living at maturity
*Cell walls unthickened
*Role = photosynthate transport
Evolution of Roots
*Roots are organs that anchor vascular plants
*They enable vascular plants to absorb water and nutrients from the soil
*Roots may have evolved from subterranean stem
Evolution of Leaves
*Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis
*Leaves are categorized by two types:–Microphylls, leaves with a single vein–Megaphylls, leaves with a highly branched vascular system
*According to one model of evolution, microphylls evolved first, as outgrowths of stems
Sporophylls and Spore Variations
*Sporophylls are modified leaves with sporangia
*Sori are clusters of sporangia on the undersides of sporophylls
*Strobili are cone-like structures formed from groups of sporophylls
Sporophylls and Spore Variations 2
*Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual gametophyte
*All seed plants and some seedless vascular plants are heterosporous
*Heterosporous species produce megaspores that give rise to female gametophytes, and microspores that give rise to male gametophytes
