Chapter 27 Plant Kingdom (Spore plants)

Characteristics of plants :

1) contain chlorophyll a and b
2) store carbohydrate as starch
3) have a cellulose cell wall
4) usually terrestrial (growing on land) : waxy cuticle (reduces water loss)
stomata in leaf to allow gas exchange
5) alternation of generations : a haploid gametophyte produces gametes that fuse to form a diploid sporophyte. The sporophyte, in turn, produces haploid spores by meiosis which grow into another haploid gametophyte.

Trends in plant evolution :
From : gametophyte dominant To : sporophyte dominant
From : need water for reproduction To : no water needed

There are two main phyla of spore plants that lack vascular tissue. These are the non-vascular plants.

1) Phylum Bryophyta ( Mosses )

20,000 species worldwide. Lack vascular tissue. They are gametophyte dominant (the gametophyte lasts much longer than the sporophyte). Animation Rhizoids anchor the plant.
Need water to reproduce : antheridia produce sperm and archegonia produce eggs

Spores are wind dispersed : some species have peristome teeth around the capsule to release spores in dry weather. Moss

example : Sphagnum peat moss ( used commercially for holding moisture in the soil). Sphagnum can hold 20 times its own weight of water. It stores water in dead cells and creates acid conditions in peat bogs. Enzymes & peat bogs Bog bodies
Bog snorkelling could be the next Olympic sport! Bog snorkelling

2) Phylum Hepaticophyta (Liverworts)

6,000 species. Liverworts and mosses are the oldest land plants, with fossils dating back almost 500 million years. Fossils
Restricted to wet areas : lack cuticle, and lack vascular tissue. Gametophyte dominant (like bryophyta). Sporangium may have elaters to shoot out the spores.

Asexual reproduction by gemmae, which are dispersed by rain.
example : Marchantia the gametophytes are dioecious (separate males and females )

Sexual reproduction : antheridia are on round topped stalks.
archegonia are on palm tree like stalks ( with lobes instead of a circular disc on the top).

Vascular plants

 Vascular plants carry liquids in special tissue called vascular tissue :
xylem carries water and minerals from the roots (upwards)
phloem carries sucrose and nutrients from the leaves (downwards).

In vascular plants the sporophyte is dominant (unlike bryophyta and hepaticophyta). They can reproduce either using either spores (single celled) or seeds (made of many cells).

Spore plants

1). Phylum Psilophyta

They look very similar to 400 million year old fossils.
They have no roots or leaves, just a photosynthetic stem. They can either grow in the ground or be epiphytes (growing on the stem or branches of another plant). They grow in South Florida and other tropical and sub-tropical areas.
The underground rhizome produces a dichotomously branched stem.
Sporangia produce haploid spores, which are not round, but more bean-shaped. Psilophytes
Example : Psilotum.

2). Phylum Lycophyta

1,000 species. Common name: club mosses (although they are NOT closely related to mosses).
They formed vast forests 300 million years ago (coal is mainly fossilized lycophyta). Present day survivors are small and mainly tropical.
The top of the sporophyte has the clustered sporangia forming a strobilus

Examples : Lycopodium is homosporous : only 1 type of spore is formed, which grows into a bisexual gametophyte.
The spores of Lycopodium are tiny and burn well, used in old flash photography, and fire-breathers in the circus.

Selaginella is heterosporous : produces a large megaspore which grows into a female gametophyte and a small microspore which grows into a male gametophyte.

3). Phylum Sphenophyta (horsetails)

Only 1 genus survives today : Equisetum. Stems are jointed, with leaves in whorls. Horsetails

Stems are strengthened with silica (common name "scouring rushes" because they were traditionally used for cleaning out, or scouring, pots and pans). Spores are produced in strobili, which are formed on separate fertile shoots.

The gametophyte is photosynthetic.

4). Phylum Pterophyta (ferns)

15,000 species. The fronds are usually divided into small pinnae. Florida ferns. Sporangia on underside of the frond may be clustered together to form sori. Animation. In some species the sporangium may have an annulus or ring of thickened cells, which in dry conditions suddenly flick the spores out of the sporangium.

Ferns are usually homosporous. The gametophyte is typically small, heart shaped, photosynthetic and needs wet conditions.

Sporophytes are well adapted to dry areas.

Example : Pteridium ( bracken fern ). It spreads asexually using rhizomes and is a common invasive weed of pastures. Horses and cattle will not eat it because it produces toxic chemicals including cyanide.

Other ferns can absorb toxins, such as arsenic, from the soil, so could be used to decontaminate sites. Arsenic was used to make pressure-treated lumber and many sites in Florida have soil contaminated with arsenic. UF Research

 Last edited January 2009, by David Byres, dbyres@fccj.edu