Chapter 28: Plants Without Seeds:

From Water to LandMeredith Patterson &

Sarah Graham

Ch. 28 Overview

1. The evolution of water plants to land plants2. The characteristics of vascular and nonvascular

plants3. The evolution of land plants and their various

structures 4. The different clades of modern day plants

Water Plants to Land PlantsLand plants are monophyletic, meaning they all descend from a single common ancestor.

The closest relatives of land plants are Charales and Coleochaetales, or “Green Algae.”

Land Plants Arose from a Green Algal CladeColeochaetales and Charales both retain the egg in the parental organism, as do land plants.

Charales are thought to be the sister-group of land plants because of the following synapomorphies:

plasmodesmata join the cytoplasm of adjacent cells

growth is branching and is from the tip

mechanics of mitosis and cytokinesis

chloroplast structure

Adaption to Life on LandCharacteristics that distinguish land plants from green algae:

Cuticle, waxy covering that retards water loss

Stomata, small closable openings in the leaves and stems, regulate gas exchange

Gametangia, organs that enclose plant gametes and prevents them from drying out

Embryos, young plants contained within a protective structure

Certain Pigments protect from mutagenic ultraviolet radiation

Spore walls containing a polymer, protect the spores from desiccation and resist decay

A mutual association with fungus that promotes nutrient uptake from the soil

Alternation of Generations

The life cycle includes both a multicellular diploid stage and multicellular haploid stage. Mitosis produces gametes, while meiosis produces spores that will develop into the multicellular haploid organism.

Vascular vs. Nonvascular PlantsLand Plants are defined as either vascular or nonvascular.

Vascular (Tracheophytes)- possess well developed systems that transport materials through the cell body, they all contain tracheids.

Examples: Ferns, Horsetails, Conifers, Flowering Plants

Nonvascular (Bryophytes)- lack tracheids

Examples: Liverworts, Hornworts, Mosses

The Evolution of Vascular PlantsThe existence of vascular plants was launched by a single evolutionary event: the production of a new cell type, the tracheid.

Since then, vascular plants have been evolving for almost half a billion years

The earliest vascular plants had simple vascular systems, but lacked tracheids and roots; they were anchored to the soil by horizontal portions of stem called rhizomes.

Arising from rhyniophytes were lycophytes (club mosses and their relatives) and monilophytes (ferns and fern relatives). New features arose such as true roots and true leaves.

It is probable that roots had their evolutionary origins as branches;a branch presumably penetrated the soiland branched further.

Furthermore, two different types of leaves eventually evolved: microphyll and megaphyll.

Early vascular plants were homosporous, but a system with two distinct types of spores evolved somewhat later; this is known as heterospory.

Present Day: Many plants have a well-developed vascular system consisting of two types of vascular tissue: xylem and phloem. Vascular plants include the club mosses, ferns, conifers, and flowering plants.

The Major Clades of Seedless PlantsNonvascular land plants clades:

liverworts, mosses, and hornworts

Seedless vascular plant groups:

lycophytes (club mosses and their

relatives) and the monilophytes

(horsetails, whisk ferns, and

leptosporangiate ferns)

With the evolution of seeds came gymnosperms and flowering plants.

Works CitedHillis, David M., H. Craig Heller, and May R. Berenbaum. "Plants Without Seeds: From

Water to Land." Life; The Science of Biology. By David Sadava. 9th ed. N.p.: Sinauer Associates, n.d. 588-606. Print.