Chapters 26 and 32: Key Concepts

• Evolution of Seed Plants • Diversity and Reproduction of Gymnosperms • Diversity and Reproduction of Angiosperms • Reproduction in Seed Plants Major Groups

300,000+ species of plants Most (+260,000 species) are seed plants Early Seed Plants • Origins of characteristics of living seed plants: late Devonian period ~380 mya • EX: Archaeopteris was a heterosporous tree with a woody stem, but it did not bear • Fossil from genus Elkinsia provides the earliest evidence of seed plants (~360 mya) Characteristics of Seed Plants

• Seeds and Pollen grains are unique characteristics separating seed from seedless vascular plants • Seed: dispersal unit of plants with an embryo + nutrients surrounded by protective coat • Pollen Grain: structure containing the male gametophyte of the plant • Changed evolution of plants= advantage for reproduction and dispersal in dry terrestrial environments • increased diversity • Enabled them to become primary producers in most terrestrial Seed Plant Characteristics • Sporophyte stage is dominant • Gametophyte stage has been reduced to a cluster of microscopic cells • Seed plants are heterosporous Pollen grains • Produce two types of spores and ovary of a • Spores develop into either male or female flower gametophytes

Ovulate and pollen cones on pine tree Pollen • Pollen grain: male gametophyte enclosed within the pollen wall • Allows for long-distance dispersal of male gametes by wind, water, and animals • Protects male gamete from dry conditions on land

• Pollination: transfer of pollen to part of a seed plant containing ovules Seeds provide some evolutionary advantages over spores… • Can remain dormant for days to years • wait until conditions are favorable for germination • Contains a supply of stored food • Endosperm • Allows for long distance dispersal by wind, water or animals Gymnosperms have a “naked seed”

• Three key features of the Gymnosperm life Ovulate and pollen cycle characteristics cones on pine tree 1. separate female and male gametophytes -can be on same plant (monoecious) or different plants (dioecious) 2. pollen cones and ovulate cones 3. pollination by wind and insects 4. Tracheids: transport water and solutes in the vascular system Life Cycle of Conifers Gymnosperms consist of four phyla:

Phylum Ginkgophyta ▪ Consists of a single living species, Ginkgo biloba ▪ High tolerance to air pollution and is a popular ornamental tree

Phylum Cycadophyta ▪ Large cones and palm like leaves ▪ Thrived during the Mesozoic, but most of the few surviving species are endangered -Diverse appearances-some are tropical, Phylum Gnetophyta others live in deserts -Considered closest to angiosperms *only gymnosperm group to produce true xylem tissue Phylum Coniferophyta

• Largest of gymnosperm phyla • Most are evergreens • Carry out photosynthesis all year round • Advantage in cold and dry weather • Still dominate boreal forests or taiga in northern latitudes Angiosperms have “covered seed” Single phylum: Anthophyta • 2 key adaptations • Flowers: structure specialized for sexual reproduction • Pollinated by insects or other animals, water or wind • Fruits: formed when ovary wall thickens + matures • protect seeds • aid in dispersal Flower Structure Most angiosperms have perfect flowers: produce both male and female floral organs

Exceptions: Monoecious plants can have male flowers and female flowers on same plant Ex: Corn plant

Dioecious have male and female flowers on separate plants Corn Plant

• has both staminate (male) and carpellate (female) flowers • Staminate flowers, which are clustered in the tassel at the tip of the stem, produce pollen grains • Carpellate flowers are clustered in the immature ears. • Each strand of silk is a stigma • The corn kernels are seeds that develop on the ear after fertilization Life Cycle of Angiosperms

Double fertilization- unique characteristic of angiosperms pollen tube discharges 2 sperm into ovule: 1 sperm fertilizes egg, other combines with two nuclei in the central cell of the female gametophyte, initiates development of food- storing endosperm Self-Fertilization • Some flowers can self-fertilize= ensures every ovule will develop into a seed • “selfing” • reduces genetic diversity among offspring • Many species have evolved mechanisms to prevent selfing • Dioecious species have staminate flowers (lacking carpels) and carpellate flowers (lacking stamens) on separate plants • Some monoecious species have stamens and carpels that mature at different times or spatially arranged to prevent selfing • Most common mechanism is self-incompatibility= reject its own pollen • Recognition of “self” pollen is based on S-genes • Some plants reject pollen that has an S-gene matching an allele in the stigma cells Methods of Pollination in Wind-pollinated species release large Angiosperms amounts of pollen Pollination= transfer of pollen from anthers to stigma

Aquatic species rely on water currents Most angiosperms depend on animal pollinators Pollination by Bees • ~ 65% of all angiosperms require insects for pollination • bees most common generalist insect pollinators • Bee-pollinated flowers are typically brightly colored and have a sweet fragrance • “Nectar guides” • ultraviolet markings direct bees/insects to nectar-producing glands

Common dandelion Common dandelion under normal light under ultraviolet light Bees and Plants • Bees are one of the most common generalist pollinators • Evolutionary relationship with • Bees originated during mid to late Cretaceous period

• Currently, there is a decline in bee populations • ~50% global loss in past 50 yrs • Recently, collapses of entire bee colonies have been reported • Pesticides • Parasites • Non-native Species Bees and Plants Loss of Bees= Loss of service • Less pollination= decline in flowering plants • Change in plant communities in natural systems • Decreased food supply for humans • Bees pollinate ~30% of human food supply • Value of service =$15 billion/yr in US

KEYWORD FOR PARTICIPATION QUIZ: BEES Evolutionary Links with Animals Animals influence the evolution of plants, and vice versa • “Co-evolution” • EX: animal herbivory selects for plant defenses • EX: pollinators and flowering plants develop mutually beneficial adaptations Coevolution Between Plants and Pollinators Shapes and sizes of flowers often correspond to pollen-transporting parts of their animal pollinators Seed and Fruit Development • After double fertilization, each ovule develops into a seed • Embryo endosperm enclosed by protective seed coat • Seed dehydrates & enters dormancy • Mature seed= 5–15% water • Ovary develops into a fruit enclosing the seed Seed Dormancy: An Adaptation for Tough Times • Increases chance of germination occurring at a time & place most advantageous to the seedling • Germination often requires specific environmental cue, such as temperature or lighting changes • Most seeds remain viable after a year or two of dormancy, but some last only days and others can remain viable for centuries

Silene stenophylla grows in Arctic of • Researchers germinated seeds after 32,000 years frozen in ice Fruit Structure Tomato Ruby grapefruit

Nectarine Fruits can be fleshy or dry

Hazelnut

Milkweed Mechanisms that disperse seeds by explosive action Fruit adaptations Wings can help with dispersal Seeds within berries and other edible fruits

Barbs Basal Angiosperms

Evolution of Angiosperms ▪ Darwin called the origin of angiosperms an “abominable mystery” due to their sudden and geographically widespread About 100 species appearance in fossil record composing three Water▪ Angiosperms lily originatedStar anise ~140mya (Illicium ) small lineages + (Nymphaea& diversified over 20- to 30-million- “Reneyear Gerard”) period Magnolidae ▪ Features of ancestral and basal constitute the basal taxa (Amborella, water lilies, star anise) early angiosperms were 300 angiosperms likely small-flowered, woody shrubs with simple water- conducting cells

Amborella trichopoda Magnolidae consist of about 8,000 species, including both woody and herbaceous plants -more closely related to monocots and eudicots than basal angiosperms Cinnamon

Avocado

Nutmeg

Southern magnolia (Magnolia grandiflora) Monocots and Dicots About one-quarter of angiosperms, ~ 70,000 species, are monocots The largest groups are the orchids, grasses, and palms

More than two-thirds of angiosperms, ~170,000 species, are eudicots -include large legume family and rose family Monocots and Eudicot Characteristics

Embryos Leaf venation Stems Roots Pollen Flowers

Monocot Characteristics

Root system Pollen Floral One Veins Vascular usually grain with organs cotyledon usually tissue fibrous one opening usually in parallel scattered (no main multiples root) of three

Eudicot Characteristics

Floral Two Veins Vascular Taproot Pollen organs cotyledons usually tissue (main root) grain with usually netlike usually usually three in multiples arranged present openings of four in ring or five Humans depend on seed plants Most of our food comes from angiosperms 6 crops yield 80% of calories consumed by humans

Wheat Rice Corn Potatoes Cassava

• Other edible products: sugar, tea/coffee, chocolate, fruit and vegetables, spices Humans depend on seed plants

Wood is harvested for… Commercial goods

Fuel

Construction Humans depend on seed plants Secondary compounds of seed plants are used in medicines In the tropical rainforest alone, 2000+ species identified w/ anti-cancer properties <1% of plant species Medicinal Plants of the Rainforest have been screened for medicinal uses Deforestation and Loss of Biodiversity But yet at a global level, we are losing 80,000 acres daily; another 80, 000 degraded Source: Scientific America Don’t Forget…

• Submit the Keyword: Bees to the Module 7 Participation Quiz • Quiz 5 is due Monday, October 19th, 11:59 pm