Science 2.3 "What Are Gymnosperms?"

evergreen

a plant that retains its leaves all year long

deciduous

a plant that drops its leaves in the fall

conifer

a cone-bearing plant w/ needlelike or scalelike leaves

gymnosperms

- a group of vascular plants w/ exposed seeds that is divided into four divisions

gymnosperm divisions

Cycadophyta, Gnetophyta, Coniferophyta, Ginkgophyta

Cycadophyta

• a gymnosperm division of mostly everygreen plants

• ex: cycad

cycad

• in the cycadophyta division

• an evergreen plant w/ stems that resemble thick trunks

• height is 2 m - 20 m

• some leaves are similar to palm leaves, but aren't actually palm trees

• it bears cones

• grows in tropics + subtropics

• leaves' base is arranged in a tightly packed spiral

palm tree and cycad

have a difference of the palm tree being a flowering plant while the cycad is a cone bearer

ginkgophyta

• a gymnosperm division w/only one living species: Ginkgo biloba

• males bear cones w/ pollen

• females produce soft, fleshy cones that look like apricots + have a slightly rotten odor that helps the tree complete its life cycle

• its nickname "maidenhair" comes from its fan-shaped leaves

• deciduous + turn golden yellow in fall

gnetophyta

• a gymnosperm division that has 3 living genera: Ephedra, Gnetum, Welwitschia

• are mostly evergreens

ephedra

a genera of Gnetophyta w/ shrubs + vines that grow in dry areas of the world
- ex: ma huang - a Chinese plant used for the drug, ephedrine, for decongestants

gnetum

a genera of Gnetophyta w/ woody vines, shrubs, + small trees that grow in tropical + desert climates

welwitschia

a genera of Gnetophyta w/ only one plant named "Welwitschia" + are only found in the desert of Southwestern Africa
- it has a large storage root + 2 long permanent leaves which are torn by the wind to make it look like many leaves

coniferophyta

• a division of gymnosperms of mainly evergreen trees or shrubs

• they dominate enormous forests in Europe, Asia, + North America

• height: 8 m (ex: pygmy pine in New Zealand) to 110 m (redwoods in California)

• male + female cones develop on different branches of the same tree or shrub (unlike other 3 divisions)

scales

indiviual plates that cones are made of and contains the reproductive structures

female cones

woody, large, easy to see cones, + produce ovules (eggs)

male cones

smaller cones + produce pollen

gymnosperm life cycle

• reproduce w/ seeds

• gametophyte stage of reproduction occurs within cones (differs from moss because it is inside + not outside)

• produces both male + female cones

• doesn't need water for fertilization due to pollen transported by wind

• while seed forms, the embryo develops in the protected + moist enviornment of a female cone

• a supply of food + water inside the embyo will allow it to grow into a new gymnosperm

alternation of generations in conifers

1. pollen forms on the male cone scales (gametophyte stage)

2. ovules (eggs) form at the base of scales of female cones + mature to form eggs. (gametophyte stage)

3. In spring, released pollen from male cones are carried by wind to female cones + get pollinated. It will sprout a pollen tube + reach the female gametophyte. The gametophyte will release two sperm cells. One will unite w/ the egg + form a zygote

4. A sporophyte zygote develops into an embryo + then into a seed in the female cone that is protected w/ a thick seed coat. It will release the seeds in right conditions

5. The seeds fall to the ground + sprout into a new gymnosperm sporophyte