Gymnosperms 1

Heterosporous Include what

All seed plants

• Megaspores — megagametophytes

• Microspores — microgametophytes

Immature Ovule

Megasporangium producing megapores

• Surrounded by nucellus and 1-2 integument layers

• The fertilized ovule becomes an embryo

Seed includes

• Embryo

• Stored food

• Seed coat

Retention of megspore in megasporangium

• “spore” are no longer released

• Reduction of # megaspores produced (1 functional)

• Formation of female gametophyte inside

Evolutionary Sequency (the seed)

Formation of integumentary around megaspororgium and modification of the apex of megasporogium to receive microspores (pollen)

Five Extant phyla

• Coniferophyta

• Cycadophyta

• Ginkgophyta

• Gnetophyta (Gymnosperms)

• Anthophyta (Angiosperms)

Progymnosperms

Intermediate between seedless vascular plants and seedless vascular plants and seed plants (ex: archaepteries)

• Production of wood (growth in bulk) and heterospory (predates seeds)

Phylum Coniferophyta Conifers (Characteristics)

• Stems (Secondary growth)

• Needle-like leaves (diversification during drylands/cold)(ecological advantage).

• Think cuticle

• Hypodermis

• Sunken stomata

• Resin ducts

Reproduction in pine pollen cones

• Microsporophylls arranged spirally (2 microsporangia on lower surface).

• Microsporagnium contains microspore mother cells

• Meiosis microspore develops into pollen gain (2 prothallial cells, generative cell, tube cell)

Seed scale complex

The modified branch system consists of:

• Ovuliferous scale

• 2 Ovules on the upper serface

• Subtending sterile bract

Ovule consists of

• Megaspore mother cell and multicellular nucellus, and integumentary with an opening (micropyle)

Megaspore mother cell

• Meiosis (4 megaspores (1 functioning))

• Development of megagametophyte (Slow)

• Begins 6 months after pollination

Pollination/Fertilization in Pines (Megagametophyte)

• 1 megaspore undergoes mitosis

• Results: 2000 free nuclei initially

• 15 months after pollination, 2-3 archegonia with egg cells from.

Pollination/Fertilizaton in Pines (microgametophyte)

• 1 year after pollination, the generative cell divides

• Results: sterile cell (Stalk cells) and spermatogenous cell (body cell).

• Before the pollen tube reaches the megagametophyte, the spermatogenous cell divides into 3 sperm.

Tallest tree

Sequoia sempervirens

Largest Tree

Sequoiadendron giganteum

Rarest Tree

Wollemia nobilia

Living fossil

Mestasequoia

• Dawn redwood, Yangtze River

• Thousands of seeds are distributed widely all over the world.