Chapter 11 Spore Plants

Chapter 11 : Spore plants 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 the dichotomously branched stem. Sporangia are in groups of 3 fused together. 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. They grow next to water. 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. Sporophytes are well adapted to dry areas. The fronds are usually divided into small pinnae. Sporangia on underside of the frond may be clustered together to form sori. 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, and photosynthetic. Ferns 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 like 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.