Plant Diversity II: the evolution of seed plants Chapter 30 Plant Diversity II: the evolution of seed plants

Section 30-1 A lot of terrestrial adaptations contributed to the success of seed plants. These adaptations include the seed, the reduction of the gametophyte generation, heterospory, ovules, and pollen. Bryophyte life cycles are mainly dominated by the gametophyte generation, but seedless vascular plants mainly have sporophyte-dominated life cycles. Seedless vascular plants have very small gametophytes however are visible to the naked eye. The gametophytes of seed plants are VERY VERY small and develop from spores that are kept within the moist sporangia of the parental sporophyte.

COntinuation Almost all seedless plants are homosporous, producing a single kind of spore that forms a hermaphroditic gametophyte. It is thought that seeds most likely had homosporous ancestors An important thing to remember is that all seed plants are heterosporous, producing two different types of sporangia that produce two types of spores. Megasporangia make megaspores, which produce a female (egg- containing) gametophytes. Microsporangia on the other hand make microspores, which produce a male (sperm-containing) gametophytes.

Cont. Seed plants produce ovules . Layer over layer of sporophyte tissue, integuments, wrap , encase and help protect the megasporangium. Gymnosperm megaspores are surrounded by one integument. While on the other hand angiosperm megaspores are surrounded by two integuments. An ovule is made of the megasporangium, megaspores, and integuments.

Cont. The microspores develop into pollen grains that are released from the microsporangium. The pollen grains are are covered with a tough coat that has sporopollenin. Then they are carried by wind or animals and moved to a new location where pollination occurs. The pollen grain germinates and grows as a pollen tube into the ovule, where it delivers one or two sperm into the female gametophyte.

Section 30-2 The ovules and seeds of gymnosperms develop on the surfaces of modified leaves that usually form cones . When in contrast, ovules and seeds of angiosperms develop in enclosed chambers called ovaries. There are four different types of gymnosperms that I while discuss in the next couple slides.

Phylum Ginkgophyta This is the smallest one out of all the groups because it only contains one species , Ginkgo biloba. This is a popular ornamental species because of its fanlike leaves that turn gold in fall before they fall off. Landscapers usually plant only male trees because the coats of seeds produced by female plants produce a repulsive odor as they decay. That smells really bad.

phylum Cycadophyta the species in this phylum have have large cones and palmlike leaves. As of right now 130 species of cycads are living right now with these characteristics . They are the third largest phylum out of all four. Cycads flourished mainly in the Mesozoic era, they even had it named after then as it became known as the “Age of the Cycads”

Phylum Gnetophyta This phylum has three very different genera. Weltwitschia plants, from deserts in southwestern Africa, have straplike leaves that are among the largest known leaves. Very weird and unheard of leaves but amazingly good. Then there are the gentum species which are tropical plants and vines . Ephedra is a shrub of the American deserts. And those are the three genera .

Coniferophyta This is the class that the confifers belong to . The word and concept conifer comes from the reproductive structure, the cone, which is a bunch of scalelike sporophylls bunched together. Although there are only about 600 species of conifers, a few species dominate vey big and broad forested regions in the Northern Hemisphere where the growing season is short. Conifers include pines, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods.

continuation Most conifers are evergreen, retaining their leaves and photosynthesizing throughout the year pretty much meaning they never stop photosynthesis, and never really fall off. Some conifers, like the dawn redwood and tamarack, are deciduous, dropping their leaves in autumn. Meaning that when autumn comes around they begin to lose there leaves.

Section 30-3 Angiosperms, mainly known as flowering plants, are vascular seed plants that produce flowers and fruits. They are the most unique and geographically spread of all plants, including more than 90% of plant species. There are about 250,000 known species of angiosperms. The phylum Anthophyta is the phylum that all angiosperms belong to. The flower is a structure the angiosperms have adapted for very successful sexual reproduction.

Continuation In the species of angiosperms, insects and other animals or the wind transfer pollen from one flower to female sex organs of another. Most of the dense populations with a lot of the population in the same area of occurs because of wind pollination. A flower is specialized to have up to four modified leaves on it : sepals, petals, stamens, and carpals. The sepals are around at the base of the flower are modified leaves that are usually green and enclose the flower before it opens.

Continuation The petals lie inside the sepals. These are often brightly colored in plant species that are pollinated by animals. They usually lack bright coloration in wind-pollinated plant species. Sepals and petals are sterile parts, not directly involved in reproduction. Stamens which are the male reproductive organs, are sporophylls that make microspores that will being to make pollen grains containing male gametophytes.

continuation Carpals are female sporophylls that produce megaspores and their products, female gametophytes. At the tip of the carpal is a sticky thing that receives pollen. A style leads to the ovary at the base of the carpal. Ovules are protected inside the ovary,

30-4 Like other organisms, we depend on photosynthetic organisms for food production and oxygen release. However, we use technology to manipulate or select plants that maximize the harvest of plant products for human use. We rely on seed plants for food, fuel, wood, and medicine. Flowering plants provide nearly all our food. Just six crops—wheat, rice, maize, potatoes, cassava, and sweet potatoes—yield 80% of all calories consumed by humans. Modern crops are the products of a relatively recent burst of genetic change, resulting from artificial selection after the domestication of plants 13,000 years ago. In maize, key changes such as increased cob size and removal of the hard coating of the kernels may have been initiated by as few as five gene mutations.