Plant Diversity II The Seed Plants

Evolution and Ecology Derived from a single common ancestor. Five phyla Angiosperms (flowering plants) Gymnosperms (four phyla of nonflowering plants) Dominated land for 350 million years

Common Characteristics 1N gametophyte is reduced so much that it acts as a reproductive organ within the 2N sporophyte Female gametophyte makes eggs Male gametophytes are pollen grains containing sperm. Waterproof, dispersed by wind or animals Reproduction independent of water

Seeds consist of . . . Embryonic plants A supply of food for the embryo as it develops roots and leaves A protective coat, allowing the embryo to remain dormant until conditions are favorable for growth

Gymnosperms / Coniferophytes. . . Gymnosperms include conifers, cycads, ginkgoes, & gnetophytes Name means “naked seed” abundant in colder latitudes and higher dry elevations

Characteristics of Conifers pines, firs, spruce, hemlock, cypresses Adapted to dry, cold conditions leaves are thin needles with thick cuticle retain leaves all year produce antifreeze resin in sap

Conifer Reproduction Sporophyte (tree) develops male & female cones Male cones are smaller and delicate, disintegrating after releasing clouds of pollen grains Female cones are large w/ woody scales Each scale has two 1N female gametophytes, each producing eggs

Conifer reproduction cont. . . After a pollen grain (male gametophyte) lands on a female cone, it sends out a slowly growing pollen tube that takes 14 months to reach the eggs. After fertilization, seeds develop and are released when the female cone matures and the scales open.

Characteristics of Angiosperms Flowers attract animal pollinators Extremely diverse in size, form and habitat                        

2 Angiospermophyte Divisions Hydrophytes Adapted for aquatic/moist environments Xerophytes Adapted for dry climates

Angiosperm Reproduction Dominant sporophyte that produce and nurture tiny male (pollen grains) and female (embryo sacs) gametophytes within flowers. Gametophytes produce gametes and fertilization occurs within ovaries of flower. Pollen grains dev from microsporangia in anther. 2N Microspore mother cells in microsporangia produce microspores by meiosis wc/ develop into pollen grains

Diploid ovule contains a 2N megaspore mother cell wc/ produces 1N megaspores Three disintegrate, one survives, divides by mitosis to produce 7 cells. One cell becomes the egg, one large central cell has two haploid nuclei These will fuse with sperm to form endosperm

Angiosperm reprod cont. . . Pollen grains lands on stigma of female, pollen tube grows thru style to ovary. Inside each pollen grain are 3 nuclei One nucleus forms pollen tube, one fertilizes egg, other fuses with polar nuclei to form 3N primary endosperm Endosperm forms food for embryo

Angiosperm reproduction. . . 2N zygote forms the embryo and the endosperm is the food Seeds are enclosed within fruits (the ripened ovaries of the flowers). Fruits entice animals to disperse seeds. Seeds are dispersed through animal digestive tracts or attached to fur.

Monocots and Dicots Monocots Dicots Grasses, corns, lilies Seed in one piece (cotyledons) Parallel veined leaves Flower petals in threes Dicots most trees, shrubs, herbs Seeds in two pieces (cotyledons) Branched veined leaves Flower petals in fours

ANGIOSPERMS The flowering plants Spring crocus Crocus vernus

Flower structure Flowers are reproductive structures The have evolved to send and receive pollen from one flower to another This is process of pollination Flowers are developed from a series of modified leaves These leaves are arranged in a rings (whorls)

Types of pollination Wind Animal Water Bumble bee Bombus hortorum on red clover Trifolium pratense Yorkshire fog grass Holcus lanatus

Animal pollination Usually insects Also other flying animals e.g. hummingbirds or fruit bats Cerambycid beetle pollinating bramble Rubus fruticosus

Flower structure Dog rose Rosa canina

Pollination Pollen grains contain the male gametes of the plant They are picked up by a pollinator and transferred to another flower Plants tend to specialize in pollinators This ensures the pollen is delivered to same species of plant

Pollination Small skipper Thymelicus flavus on marsh thistle Cirsium palustris

Pollination The honey bee Apis melifera on marsh thistle Cirsium palustris © 2008 Paul Billiet ODWS

Pollination Fox glove flowers Digitalis purpurea Some flowers are highly specialised to encourage only one type of insect © 2008 Paul Billiet ODWS

Pollination Most species of flowering plants are monoecious Pollen from a flower could land on the stigma of the same flower or another flower on the same plant = self pollination Pollen transferred from the anther on one flower to the stigma of another flower on a different plant = cross pollination © 2008 Paul Billiet ODWS

Fertilisation Pollination ≠ Fertilization The male gamete (the male nucleus) has to get to the egg cell The egg cell lies in an ovule in an ovary at the centre of the plant The pollen grain germinates on the stigma It grows a pollen tube down the style It male nuclei travel down the pollen tube to the ovule © 2008 Paul Billiet ODWS

Fertilisation Pollen grain Stigma Style Ovule Embryo sac Ovary Pollen tube Ovary © 2008 Paul Billiet ODWS

Fertilization Embryo sac Polar nuclei Egg cell Micropyle © 2008 Paul Billiet ODWS

Fertilization Pollen grains of the daisy Bellis perennis © 2008 Paul Billiet ODWS

Fertilisation Germinating pollen grains of blue bell, Hyacinthoides non-scripta © 2008 Paul Billiet ODWS

The double fertilization Pollen tube Pollen tube entering micropyle Male nucleus + egg cell = zygote (2n) Male nucleus + 2 polar nuclei = endosperm nucleus (3n) Ovule © 2008 Paul Billiet ODWS

From flower to fruit Marsh marigold Caltha palustris © 2008 Paul Billiet ODWS

Fruits and seed dispersal Animal dispersal Strawberry Fragaria vesca Explosive dispersal Bird’s foot trefoil Lotus corniculatus Animal dispersal Wood avens Geum urbanum Wind dispersal Ragwort Senecio © 2008 Paul Billiet ODWS