Seedless Vascular Plants

Seedless Vascular Plants

Ferns (Monilophyta) & Lycophytes (Lycopodiophyta)

Characteristics

• sporophyte dominant; free living

• true xylem and phloem (vascular system)

• lignified cell walls for xylem and supporting tissue (sclerenchyma)

• true roots, stems, leaves

• capacity to branch - apical meristem activity

Lycophyte Taxa

• Club Mosses

• Spike Mosses

• Quillworts

(small orders, families)

Lycopodiophyte Leaves

• specialized for photosynthesis

  • referred to as microphylls

Microphylls

• not broad

• single vein of vascular tissue

• evolved from stem outgrowths (enations)

• leaves of lycopodiophytes

Megaphylls

Leaves of Monilophyta

• many veins, broad

• angiosperms ad gymnosperms are thought to have evolved from fusion of branch systems

Strobili

bourne on termini of sporophyte stems

• in club and spike mosses

Club Mosses

• sporangia develop on modified microphylls (sporophylls)

  • homosporous = one type sporangium

Spike Mosses

• Sporangium develop on modified microphylls (sporophylls)

• heterosporous = two types of sporangia

Monilophyta

ferns, horsetails, and whisk ferns

• have megaphylls

Ferns

• sporophyte is dominant and gametophyte short lived

• grow as single axis (vertical shoot or horizontal axis)

• leaves = fronds

Fronds

• petiole and lamina

• mostly pinnately compound

• most several cell layers thick

  • palisade and spongy mesophyll

Fern Vascular Tissue

• surrounds central pith

• phloem on either side of xylem

Leptosporangium Development

• moslty extant species

• initiated when single surface cell on sporophyll divides periclinally = outward protrusion

• tapetum = layers of cells that nourish developing spores

  • disintegrates as they mature

Eusporangium Development

• horsetails and whisk ferns

• initiated when several surface cells undergo periclinal divisions

• tapetum persists longer

• more similar to spore generation in seed plants

Leptosporangiate Ferns

• sporangia located on underside of leaves in sori clusters

• sori covered by indusium (specialized outgrowth)

Horsetail Sporangia

clustered together on a sporangiophore → arranged into strobili

• horsetail spores have elators

Elators

long strips that are wrapped around each spore, and uncoil when relative humidity in the air drops → spores spread apart and disperse