Seedless Vascular Plants Chapter 17
Seedless vascular plants • The descendants of certain lineages of seedless vascular plants, with names such as whisk ferns, lycophytes, horsetails, and ferns,
Seedless Vascular Plants • differ from bryophytes in that the sporophyte does not remain attached to the gametophyte (is free-living) and • has well-developed vascular tissues. • It is the larger, longer lived phase of the life cycle.
Organization of the Vascular plant body • The sporophytes of early vascular plants were dichotomously branched Club moss sporophyte • Lacked roots and leaves
Shoot system Vascular system Young Club moss sporophyte
Tissue systems • Dermal- outer portion • Vascular- conductive tissues (xylem and phloem) • Ground- vascular embedded within ground • Root, stem and leaf vary in these tissues
Gametophytes • Although the sporophytes of seedless vascular plants can live on land, their gametophytes cannot because they lack vascular tissues and the male gametes must have water to reach the eggs. Seedless vascular plants typically live in wet, humid places.
Tracheids elements • Conducting cells of the xylem (water and minerals) • Have lignified wall thickening
Sieve elements • In contrast sieve elements, the conducting cells of the phloem have soft walls and often collapse after they die
Vessel elements • Principle water conducting cells in angiosperm (flowering plants) • VE evolved independently in several groups of vascular plants- Convergent evolution
Vascular tissue Located in the vascular cylinders or Steles of Roots and Stems • Primary xylem • Primary phloem • In some Vascular plants Pith (ground tissue)
Leaf precursors Found in SVP Several types of Steles- vascular cylinders that contain vascular tissue (xylem, phloem and ground tissue)
Two distinct kinds of leaves (phylls) • Microphylls- small leaves contain single strand of vascular tissue (Isoetes – long leaves) • Megaphylls- associated with stems that have either siphonosteles and eusteles • Branching veins
Reproductive Systems • All vascular plants are oogamous- have large nonmotile eggs and small sperm that swim or are conveyed to the egg • All VP have an alternation of heteromorphic generations ( sporophyte is larger and more complex than the gametophyte)
Larger and more complex than the gametophyte Free living Generalized life cycle of a vascular plant
Oogamy • Favored in plants • Only one of the kinds of gamete must navigate across a hostile environment
Homosporous Vs Heterosporous • Homosporous produces one type of spore • Heterosporous produces two types of spores • Early vascular plants are homosporous i.e. (including horsetails) and some lycophytes • Heterosporous found in some lycophytes and in all seed plants (convergent evolution)
Microspores and Megaspores • Microspores- male gametophyte • Megaspores- female gametophyte • Endosporic development (develop within spore wall) unlike the homosporous development
Evolution of the vascular plant • The gametophytes of VP have become smaller and simpler • Relatively large gametophytes of Homosporous plants are independent of the sporophyte for their nutrition • In contrast the gametophyte of many heterosporous VP and seed plants are dependent on the sporophyte for their nutrition
The Living Phyla of Seedless Vascular Plants • Phylum Lycopodiophyta • Club mosses • Lycopodium lagopus • Selaginella • Isoetes • Phylum Pteridophyta • Ferns • Water ferns- orders Marsileales and Salviniales • Psilotales • Equisetales (horsetail)
Phylum Lycopodiophyta • Lycophytes were once tree-sized but now are represented by small club mosses on the forest floor. • The sporophyte has true roots, stems, and small leaves containing the vascular tissue. • Strobili bear spores that germinate to form small, free-living gametophytes.
Lycopodiophyta- Club mosses • Most familiar type- Club mosses belong to Family Lycopodiaceae
Ferns (Pterophyta) • Most ferns have a perennial underground stem (called a rhizome). Roots and fronds arise from the rhizome. Young fronds are coiled "fiddleheads". Mature fronds are divided into leaflets. Spores form on the lower surface of some fronds. Sori are clusters of sporangia that release spores that develop into small heart-shaped gametophytes.
Vascular Tissue • Approximately 93% of plant species are vascular plants. • Vascular plants contain vascular tissue. • There are two kinds of vascular tissue: • Xylem conducts water and minerals up from the soil. The cell walls of xylem cells help support the plant. • Phloem conducts organic nutrients from one part of the plant to another. • True roots, stems, and leaves are found only in vascular plants because these structures must contain vascular tissue. • The sporophyte of vascular plants is dominant.
In most ferns, the stem is a horizontal, underground structure called a rhizome. The leaves grow above-ground (see the photograph above). • A sorus (pl. sori) is a cluster of sporangia. Sori are located on the underside of the leaves.