Lecture 15: gymnosperms

Female cones

• Megastrobilus

• Woody and larger than male cone

• Woody bracts=modified stem tissues

  • One ovule per woody bract

  • Distinct between species

Male cones

• Microstrobilus

• Herbaceous and smaller than female cone

• bract=microsporophyll (leaf driven)

  • Multiple pollen grains per bract

• Similar across species

Seed ferns

Pteridospermatophyta

• Extinct fern group

• Seed like structures in fossil record→ first gymnosperm groups

Coniferophyta: Conifers characteristics?

• Largest group 

Characteristics:

• Woody secondary growth

• Dominant tree species in very northern locations

• Needle-shaped growth

• Evergreen persistent foliage in many species

Families: Pinaceae, Cupressacea, Taxaceae

Pinaceae: what do they contain?

“traditional conifers”

Contains

• Pines

• Spruces

• Larches

• Hemlocks

• Firs

• Cedars

Pinaceae: what are their traits?

• Evergreen (M)

• Needle-like leaves

• Monoecious 

• Many have whorled branches

• Resinous

• Large female cones (mostly woody)

• Small male cones

• Wind Pollination

• Pollen has extra extension “wings”

Cupressaceae: what are their traits?

CN: cypress family

• Variable group 

Traits

• Many scale like leaves

• Woody trees or shrubs

• Cones: woody or fleshy 

Taxaceae: what are their traits?

CN: yew family

Traits: 

• Evergreen 

• Small trees or shrubs

• Female cones=SPECIALIZED

  • Single seed and a single scale that develops into a fleshy aril (resembling a fruit)

→ attracts birds, seed dispersal

Coniferophyta Lifecycle: Male structure

Sporophyte dominant; gametophyte relies on sporophyte for nutrition 

Male structure:

• Microsporophylls organized into a strobili

• Single celled microspore produced

• Microspore goes through meiosis and mitosis

  • Forms pollen (multicellular haploid organism=gametophyte)

• pollen=wind dispersed

• Pollen lands on female egg cell→germinates→releases sperm cells

Coniferophyta Lifecycle: within the cone

• Mother diploid cell undertakes meiosis

  • Produces 4 daughter cells→ 3 die→ 1 becomes megaspore

• Megaspore goes through mitosis → produces female gametophyte

  • Forms archegonia, then eggs

• Eggs =fertilized by wind-dispersed pollen

Cycadophyta: Cycads

• 2nd largest group

Characteristics:

• Woody secondary growth

• Short height

• Hard and stiff evergreen leaves

  • Pinnate

• Slowwwww growth

• Dioecious

Families:  Cycadaceae, Strangeriaceae, Zamiaceae

Cycadaceae: what is genus and traits?

CN: cycad family

• Genus: Cycas

Traits: 

• Woody

• Mostly “Palm like growth”

• Dioecious

• Female cones are megasporophylls (leaf NOT stem tissue)

Strangeriaceae: traits?

• Small family, only 3 living species

Traits:

• “Fern-like” growth

Zamiaceae: traits?

Sago-palm family

Traits:

• Palm-like

• Perennial

• Evergreen

• Dioecious

Cycadophyta: Lifecycle: male vs female?

• Both male and female structures are composed of sporophylls (spore-bearing leaves)

• Male: compound strobilus structure

• Female: megasporophylls only!

  • Doesn’t form a compound strobilus in most species

Ginkophta: Ginkos: what is unique about them? Characteristics?

• Smallest group in gymnosperms

• 1 single species: Ginkgo biloba (living fossil, survived 270 million years, most species only 1 million years), largest wild population cultivated by chinese monks for ~1000 yrs

• Used to be more diverse taxonomy

Characteristics:

• Fan-shaped leaves

• Dioecious

• Fruit-like structure for female gametophytes

  • NO cones!!!

Ginkophyta: Lifecycle: male and female

• Male structures: simplified sporophyll stobili with only two bracts

• Female structures: simplified strobili with only 2 ovules 

  • NO cones produced!

• Seed protected by stinky ahhh fruit-like substance

  • Developed from integument

Gnetophyta: Gnetidae: weird ones

Weird ahhh species

Was once more diverse alas

Contain vessel elements and tracheids!!

• Evolved independently of vessel elements in angiosperms

• Closest evolutionary link to angiosperms

Characteristics:

• Share little in common (other than DNA)

• Have evolved to be SPECIALIZED in their respective habitats

Gnetum sp.: what does it look like

• Mainly woody tropical vines or trees

• Superficially look like angiosperms

  • Cones not flowers though

Ephedra sp.: what does it look like?

Looks like grass or equisetum with cones!

Welwitschia mirabillis:

• Desert-specialist

• Two large leaves growing continuously from the base of the plant

• Only species in its order

Gnetophyta: Lifecycle: common themes?

• Highly divergent between diverse groups

• 1 common theme:

  • Double fertilization!! (only in some) In all angiosperms