LOWER VASCULAR PLANTS - These are the spore bearing plants in which the main part of the plant is diploid (sporophyte). There is a small multicellular haploid (gametophyte) portion of the life cycle, however, which lives separate often for only a short time in the wet season. This is a sporic life cycle then, with emphasis on the sporophyte. Representative phyla include; Psilophyta, Lycophyta, Sphenophyta, Pterophyta

Phylum Psilophyta - Whisk ferns Most species extinct, known only in fossil record. Look superficially like hornworts & stoneworts of the green algae.

Characteristics - have dicotomous branching like branching algae, chara. Sporophyte (diploid) is dominant vegetative part, stems and sporangia have first complete waxy cuticle.

sporangia with small sporophyll develop in protective axials of branch points and along leafless stems

There are true stems with vascular tissue but no true leaves or roots with vascular tissue

Life Cycle is sporic with emphasis on the sporophyte, a small gametophyte lives very short time producing gametes and diploid zygotes from which new sporophytes grow.

Niche - minor importance, found mainly in tropical areas. Large species exist in the fossil record. Two species known to still survive in parts of Florida
Stem cross section - protostele looks superficially like a moss stem. Cells have secondary and tertiary cell walls with lignin (woody). Dead cells of the central cylinder (stele) are more heavily lignified and dead, producing water conducting tissue (xylem) that can take up water much more efficiently by capillary action than the central canal of moss. There are also primitive phloem (food conducting) elements.

Phylum Lycophyta - club mosses, some look superficially like moss, with small crowded leaves on dichotomous branched stems. However the vegetative portion here is diploid (sporophyte).

Characteristics - This group has the first true stems leaves and roots with vascular tissue and complete cuticle

Strobilus - the cone like reproductive structures rising above the leafy plant. Meiospores (haploid) are produced all different genetically and blow in the wind. No male or female cone, or male or female meiospores. Meiospores develop into smale gametophytes that produce archegonia and antheridia and zygotes (diploid, 2n) from which new sporophyte plants arise.

Life cycle - sporic (emphasis on sporophyte) small brief gametophyte, protective reproductive structures.

Niche - Club mosses due to the true roots, well developed cuticle, well developed stomata, are much better at obtaining and conserving water. Thus during vegetative growth they can live in drier conditions and are found today in much greater range than the whisk ferns above. They still need a wet season for reproduction since the sperm are flagellated and must swim the the nonflagellated archegonia on the gametophyte.
Note leaves with veins (vascular) and heavy cuticle
Stem has an inner stele with islands of large celled xylem interspersed in the background of phloem
Strobilus (cone, 2n) has larger protective sporophylls [4] protecting sporangia [3] which are producing the meiospores which will blow in the wind to a new location and grow into the gametophyte (haploid,1n)

Selaginella - looks superfically like sphagnum moss

Isoetes - looks superfically like a whisk fern but has leaves. They produce megasporangia (produce female meiospores) and microsporangia (produce male meiospores. Sporangia are found at the base of leaves. This is one of the first species to be heterosporous, though is not the rule for the phylum

Phylum Sphenophyta - horsetails produce thin vegetative stalks with multiple branches per node (whorled branching, monopodal branching). They also produce fruiting stalks with a large strobilus or cone.

Life Cycle - sporic with emphasis on the sporophyte, most produce only one type of strobilus (cone) but are heterosporous

Leaves - rudimentary whorl at base of nodes, most photosynthesis is done by the stems. Leaves clearly have veins and vascular system.

Strobilus (cone) produce two types of meiospores (male and female) and are thus called heterosporous.

Niche - more restricted to wetland areas. They grow taller and need water readily available for life.
Strobilus (cone) has protected sporangia producing heterospores by meiosis

Horsetail stem cross section - note that the stem is hollow inside (central canal) so that water can passively move up to inner cells when surrounding water rises. These plants live by waterways, marshes, lakes, etc. They also have vallecular canals and carinal canals which are smaller in diameter to allow higher movement of water by capillary action.

These stems also have some xylem and phloem for active transport of water and food in drier conditions.

Phylum Pterophyta - ferns are the most successful group of the spore bearing plants.

Niche - While they still require much water, they have large frond leaves, photosynthetically efficient and do well as subdominants of moist forests, particularly of the tropics. Most species known only in the fossil record. Tree ferns contributed most to the fossil fuel beds. Some tree ferns survive in tropics.

Life Cycle - sporic with emphasis on the sporophyte, small heartshaped gametophyte produces archegonia, and antheridia

Fern sori - many sporangia on stalks are protected by an umbrella like cap (indusium) on the underside of leaves.

 

Fern leaf with vascular tissue, with many sporangia on underside of leaf

cross section of a fern leaf (top of second picture), an indusium (umbrella) hanging from beneath, and many sporangia between
Haploid fern gametophyte - heart shaped thallus, starts out filamentous, and becomes thalloid like liverwort. It is the size of a pin head but produces both antheridia and archegonia. Strands are rhyzoids.
Fern stem cross section - plectostele has inner ring of xylem, surrounded by phloem, embedded in lignified cortex cells to give the stem rigidity.