Unit 7. Plant Kingdom.

WARM-UP: Think of words and word-combinations you associated with plant kingdom and complete the following diagram.

VOCABULARY: Learn the following words and word combinations.

Moss liverwort hornwort starch seed fern horsetail gymnosperm angiosperm sedge rush pollen conifer pine spruce fir yew hemlock cypress redwood larch juniper cone dispersal to penetrate to decline

Guess the meaning of the following words.

Parenchyma; photosynthetic pigments; chlorophyll; cellulose; embryo; rhizomes; to evolve; climax; algae; species; to differentiate from.

Practice the following for pronunciation.

parenchyma [pə´reŋkımə]

Silurian [saı´lju(ə)rıən]

Devonian [de´vəunjən]

extinct [ık´stıŋkt]

gymnosperms [ֽdʒımnə´spз:mz]

sedge [sedʒ]

rush [r۸ʃ]

conifer [´kəυnıfə]

dioecious [daı´i: ʃəs]

crown [kraυn]

pine [paın]

spruce [spru:s]

fir [fз:]

hemlock [hemlɒk]

cypress [´saıprıs]

larch [la:tʃ]

juniper [‘dʒu:nıpə]

yew [ju:]

cone [kəυn]

pulp [p۸lp]

dispersal [dıs´pзs(ə)l]

Jurassic [dʒυ´ræsık]

READING: Read the text and do the tasks that follow.

The bryophytes represent about 25,000 species of mosses, liverworts, and hornworts. In contrast to algae, bryophytes are rarely filamentous. Instead, they are composed of cell that form tissues called parenchyma. In bryophytes, the principal photosynthetic pigments are chlorophyll a and b. Their energy reserves are stored in the form of starch, and their cell walls contain cellulose. Bryophytes are usually terrestrial. They have no vascular tissue.

500 million years ago the first vascular plants to colonize the land appear in the fossil record. A significant innovation unique to the vascular plants is the seed, which consists of an embryo and some stored food enclosed within a protective coat. The most primitive of the vascular plants are the psilophytes. They have true stems, branching from slender rhizomes. No true leaves are present. The psilophytes evolved during the Silurian period and thrived more than 300 million years ago. Many botanists believe some psilopods evolved into the ferns.

Lycophyta, or the club mosses, also appeared during the Silurian, about 400 million years ago. About 1000 species are still found throughout much of the world. Club mosses have true leaves, stems, and roots. They may have evolved from algae that penetrated the ground, occasionally sending branches above the ground. It should be pointed out, that the club mosses are not related to the true mosses, or bryophytes.

Another group of vascular plants is the Sphenophyta, commonly known as horsetails. They appear during the Devonian, around 360 million years ago, and dominated forests during the late Paleozoic era. About 250 million years ago, they began to decline. Today there are some 25 species left, most of which are relatively small. They all have true roots, stems, and leaves.

Many botanists fell that the pterophytes, or ferns, evolved from the psilophyte stock. Ferns have true roots, stems, and leaves. They first appeared during the Devonian, around 400 million years ago. Today there are about 11,000 fern species living throughout the world. Most forms are quite small, though one group, the tree ferns, is the exception. They have a woody trunk with leaves and sometimes attain heights of nearly 25 m (82 ft).

In some classifications, the remaining vascular plants are replaced in the group Spermopsida. This contains the gymnosperms and angiosperms. Gymnosperms include cycads, the ginkgoes (just one living member), conifers, and others. The angiosperms include all the grasses, sedges, rushes, and other flowering plants.

A distinctive feature of the peculiar gymnosperm phylum known as seed ferns is not that its species don’t produce spores, as true ferns do, but that instead they produce seeds.

Another unusual group, the gnetophytes, includes about 70 desert and montane species with flower-like reproductive structures. They are dioecious, produce pollen, and bear small, naked seeds. The gnetophytes appear to be relatives of the ginkgo and the conifers.

The earliest fossils of another ancient group, the cycads, date about 240 million years ago. They reached their climax about 200 million years ago, and then declined steadily, now only about 100 species survive.

Usually referred to as the conifers, this group includes pine, spruce, fir, hemlock, cypress, redwood, larch, juniper, and yew, as well as others that aren’t as well known. The conifers include about 50 genera, comprising over 600 species. Their fossil history dates back to the late Carboniferous, some 300 million years ago. Although the cone is a conspicuous feature distinguishing many members of this group, it does not appear on all conifers. For example, juniper berries are actually small cones with fleshy scales. And yews have seeds surrounded at the base by a fleshy, berry-like pulp. The pinoids are adapted for wind dispersal of their seeds. The others are adapted to animal dispersal.

The angiosperms, or flowering plants, also known as the anthophytes, are by far the most successful group of living plants, totaling some 250,000 described species. It is their flowers and fruits that differentiate them from all other plants. The earliest known angiosperm-like plants first appear during the Jurassic, about 150 million years ago.