The Early Tracheophytes: Ferns and Relatives

Tracheophytes (Early and Late) - Tracheophytes are vascular plants that posses, lignified water conducting tissue. - Tracheophytes are the vascular plants. - Prior to the evolution of tracheophytes, bryophytes were the dominant form of plant life on earth. However, having an efficient transport system enable the tracheophytes to outcompete bryophytes in many circumstances. - Unlike bryophytes, tracheophytes have a branched sporophyte that is dominant in the life cycle. - Tracheophyte Characteristics: 1) Xylem and Phloem for transport. 2) Lignified transport vessels to support the plant. 3) Roots to absorb water while also anchoring & supporting the plant. 4) Leaves that increase the photosynthetic surface. 5) Life cycle with a dominant sporophyte generation. The Early Tracheophytes are the Seedless Plants (Ferns & Relatives). The Late Tracheophytes are the Seed Plants which are the Gymnosperms (those bearing cones and having naked seeds) and Angiosperms (flowering plants that have covered seeds & fruit).

Tracheophytes (The Vascular Plants) evolved from bryophytes. Tracheophytes are highly specialized for life on land and now dominate the landscape. The Early Tracheophytes (Rhyniophytes, Lycophytes, Monilophytes) and Late Tracheophytes (The Seed Plants, which are Gymnosperms and Angiosperms) are all Tracheophytes. A Cladogram of the Early Tracheophytes. Extinct

The Early Tracheophytes (Seedless Plants) -The early tracheophytes are seedless. -They reproduce by spores. -The majority of the early tracheophytes are homosporous. However, heterospory does occur. -The early tracheophytes are successful and have sporophytes that are more tolerant of life on dry land than those of bryophytes because water movement is controlled by lignified vascular tissue, stomata and an extensive cuticle. -Water is still important for early tracheophyte gametophyte. Water outside the plant is necessary for sperm movement from antheridia (Sperm-bearing organ) to archegonia (egg- bearing organ). Therefore, moist habitats are necessary.

Division Lycophyta Lepidodendron, a dominant tree of the coal age forest. A club moss (Lycopodium obscurum), alive today. The lycophytes have laterally attached sporangia instead of terminally attached.

A Diorama Reconstruction of a Coal Age Forest. The lycophyte line reached its peak of diversity and ecological importance in the Coal Age (Carboniferous Period). Today, lycophytes represent a mere remnant of their Coal Age diversity. (Read blue box on pages ).

The following divisions make up the Monilophytes: Division Psilophyta Division Ophioglossophyta Division Sphenophyta Division Pterophyta The Monilophytes are mostly herbaceous (nonwoody) plants.

Division Psilophyta – the Whisk Ferns A whisk fern (Psilotum nudum). Members of this division are often epiphytes. An Epiphyte is a plant that grows on another plant, yet is not parasitic.

Division Ophioglossophyta - the Ophioglossalean Ferns Adder’s Tongue Fern (Ophioglossum sp.) These small plants are members of the spring flora in temperate regions and also are found in disturbed or open tropical sites. A few are epiphytes. Ophioglossum has the greatest number of chromosomes of any plant, 2n being as high as 1,250 in some species.

Division Sphenophyta – Horsetails Horsetails Only 1 genus is present (Equisetum). Stems have complex anatomy.

Division Pterophyta – True Ferns True Fern Complex leaves are varied. Sexual reproduction is usually homosporous (one type of spore, which then develops into a bisexual gametophyte). 12,000 known species 5 Orders The true ferns have a leptosporangium, (a distinct sporangium type).

True Fern Structure Stems are underground and fronds (leaves) are above ground. Remember, rhizomes are underground stems. Fiddlehead - young tightly coiled fern fronds (leaves). Know the parts of the frond (fern leaf)  rachis, pinna, pinnules.

Fern Reproduction Sori (singular, sorus) - a grouping of sporangia; especially characteristic of ferns. An individual sorus consists of an indusium, sporangia (specifically leptosporangia with annulus). The underside of a holly leaf, showing many scattered sori.

Indusium - membranous growth of the epidermis of a fern leaf that covers a sorus. A section of one sorus, showing the umbrella-like indusium that shelters the sporangia.

A leptosporangium and the role of the annulus in spore dispersal. A Leptosporangium is a distinct sporangium type. It has a long stalk and a single layer making up the wall and it has an annulus that aids in spore dispersal by flicking spores out of the sporangium.

True Fern Life Cycle a)Mature Frond b)Sori form and result in meiosis. c) A haploid spore settles on the moist ground, germinates into gametophyte. d) Archegonia, the structures that produce eggs, and the antheridia, which produce sperm, both develop on the underside of the gametophyte. e) & f) Flagellated sperm swim form antheridia to archegonia (Usually another gametophyte). g) Zygote is nourished by gametophyte. h) Embryo sporophyte develops. i) Young sporophyte develops that is rooted in the soil itself and is independent of the gametophyte.

True Fern Reproduction - Sporophyte (2n) is larger than gametophyte (n). - Some ferns can reproduce vegetatively (asexual reproduction) in the sporophyte or gametophyte bodies. - The fern life cycle usually doesn't involve animals. - Read blue box on 422.

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