BIOL 108 Topic 14

Vascular Tissues

• evolved exclusively in the sporophytes of vascular plants

• allowed sporophytes to grow tall

• only the sporophyte stage has vascular tissue

Life Cycles with Dominant Sporophytes

• sporophytes are dominant in size, complexity, longevity

• independent, branched sporophytes (better light interception)

Complex Multicellular Roots

• anchor the sporophytes of vascular plants and absorb and transport water and nutrients from the soil

Complex Multicellular Leaves

• increase the surface area of vascular plant sporophytes, allowing them to capture more solar energy for photosynthesis

Microphylls

• small leaves with single veins that possibly evolved as outgrowths of stems

Megaphylls

• large leaves with highly branched vascular systems that potentially evolve from webbing between flattened branches

Sori

• clusters of sporangia found on the undersides of sporophylls

• ex: ferns

Strobili

• cone-like structures formed from groups of sporophylls

• ex: lycophytes and most gymnosperms

Characteristics of Living Vascular Plants

• most seedless vascular plants are homosporous with sporophytes producing a single type of spore that develops into a bisexual gametophyte

• all seed plants and a few seedless vascular plants are heterosporous, producing megaspores and microspores

Lycophyta

• includes club mosses, spike mosses, and quillworts

• small herbaceous plants

• are microphyllus and are either homo or heterosporous

Monilophyta

• includes ferns, horsetails, whisk ferns, and their relatives

• morphologically diverse

Whisk Ferns

• resemble ancestral vascular plants but are closely related to modern ferns

• they have no true roots or leaves, which were lost secondarily

Horsetails

• characterized by brushy stems

• have leaves with a single vein, but they are secondarily microphyllous

Ferns

• the most diverse seedless vascular plants

• they have megaphylls

• produce clusters of sporangia on the underside of sporophylls