Chapter 29 - Plant Diversity I: How Plants Colonized Land

Many important characteristics of plants may also be found in algae. Plants, for example, are multicellular, eukaryotic, photosynthetic autotrophs, as are brown, red, and certain green algae. Plants, as well as green algae, dinoflagellates, and brown algae, contain cellulose cell walls. Green algae, euglenids, and a few dinoflagellates, as well as plants, have chloroplasts containing chlorophylls a and b.

However, charophytes are the only modern algae that share the following distinguishing characteristics with plants, implying that they are the closest living cousins of plants:

Proteins that synthesize cellulose form rings. Plant and charophyte cells feature unique circular rings of proteins inserted in the plasma membrane (small picture). These protein rings are responsible for the synthesis of the cell wall's cellulose microfibrils.

Noncharophyte algae, on the other hand, contain linear sets of proteins that produce cellulose.

Flagellated sperm structure The structure of sperm of plant species with flagellated sperm closely matches that of charophyte sperm.

A phragmoplast is formed. Plants and some charophytes have unique cell division features.

A phragmoplast, for example, is a collection of microtubules that develops between the daughter nuclei of a dividing cell. In the midst of the phragmoplast, across the midline of the dividing cell, a cell plate forms. In turn, the cell plate generates a new cross wall that divides the daughter cells.

Nuclear, chloroplast, and mitochondrial DNA studies on a diverse variety of plants and algae show that some families of charophytes, such as Zygnema and Coleochaete, are the closest extant relatives of plants. Although this data indicates that plants evolved from a group of charophyte algae, it does not imply that plants are derived from t.

• A phragmoplast, for example, is a collection of microtubules that develops between the daughter nuclei of a dividing cell. In the midst of the phragmoplast, across the midline of the dividing cell, a cell plate forms. In turn, the cell plate generates a new cross wall that divides the daughter cells.

Nuclear, chloroplast, and mitochondrial DNA studies on a diverse variety of plants and algae show that some families of charophytes, such as Zygnema and Coleochaete, are the closest extant relatives of plants.

Although this data indicates that plants evolved from a group of charophyte algae, it does not imply that plants are derived from t.

Plant-Derived Characteristics After plants separated from their algal ancestors, certain adaptations that aid in survival and reproduction on dry ground evolved. The image attatched, labled as Figure 29.3, illustrates five of these characteristics seen in plants but not in charophyte algae.

Green algae gave rise to plants. Certain types of charophytes are the closest living relatives of plants, based on morphological and biochemical characteristics, as well as similarities in nuclear and chloroplast genes.

Charophytes may withstand periodic drying at the borders of ponds and lakes thanks to a protective layer of sporopollenin and other characteristics. Such characteristics may have allowed plants' algal ancestors to thrive under terrestrial environments, paving the path for dry land colonization.

Cuticles, stomata, and multicellular dependent embryos are derived characteristics that separate plants from charophytes, their closest algae cousins. Plants first appeared more than 470 million years ago, according to fossils.

Plants then split into many major groups, including nonvascular plants (bryophytes), seedless vascular plants (lycophytes and ferns), and the two seed plant families, gymnosperms and angiosperms.

Gametophytes dominate the life cycles of mosses and other nonvascular plants. Early in plant evolution, lineages leading to the three current clades of nonvascular plants, or bryophytes—liverworts, mosses, and hornworts—diverged from other plants.

The main generation of bryophytes is made up of haploid gametophytes, such as those found in moss carpets. Rhizoids serve as a means of anchoring gametophytes to the substrate on which they develop. Antheridia req produces flagellated sperm.

• The term Sphagnum refers to peat moss and is common in large regions known as peatlands and has many practical uses, including as a fuel.

Antheridia's flagellated sperm need a layer of water to go to the archegonia's eggs.

The diploid stage of the life cycle, the sporophytes, emerges from archegonia and is connected to and dependent on the gametophytes for sustenance. They are smaller and simpler than vascular plant sporophytes, consisting of a foot, seta (stalk), and sporangium.

The earliest plants to grow tall were ferns and other seedless vascular plants.

Fossils of the ancestors of today's vascular plants date back about 425 million years and demonstrate that these tiny plants possessed autonomous, branching sporophytes and a vascular system.

Other derived features of live vascular plants evolved through time, including a life cycle with dominating sporophytes, lignified vascular tissue, well-developed roots and leaves, and sporophylls.

The lycophytes (phylum Lycophyta: club mosses, spikemosses, and quillworts) and monilophytes (phylum Monilophyta: ferns, horsetails, and whisk ferns and relatives) are seedless vascular plants

According to current data, seedless vascular plants, such as bryophytes, do not comprise a clade.

Lycophytes' ancient lineages comprised both tiny herbaceous plants and huge trees. Lycophytes are tiny herbaceous plants that exist today.

Around 385 million years ago, seedless vascular plants produced the first woods. Their expansion might have contributed to the massive global cold that occurred during the Carboniferous epoch. The rotting remains of the earliest woods were finally converted into coal.