Introduction to Gymnosperms

Outline

Introduction

Gymnosperms are an informal grouping of vascular seed plants with naked seeds (no fruits), that with angiosperms comprise the "seed plants"

they have seeds (= embryo + food supply + seed coat)

they can produce wood

Wood

Primary growth vs. secondary growth

lateral meristems

woody vs. herbaceous

vascular cambium

in gymnosperms it is:

• bifacial
• capable of unlimited growth

it produces:

xylem -- tracheids

phloem -- sieve cells

also rays, which allow radial transport in xylem and phloem

cork cambium

produces cork cells of outer bark

inner bark is phloem

a little Phylogeny

the *Trimerophyta gave rise to the *Progymnosperms

the *Progymnosperms gave rise to the *aneurophytes and *archeopterids

aneurophytes -- protostele, homosporous, simple photosynthetic structures

archeopterids -- eustele, heterosporous, evolved megaphylls

the *archeopterids begat the various extant gymnosperm divisions:

Ovule and Seed

Ovule = megaspore + megasporangium (= nucellus) + integuement

Compare and contrast with life cycle of Selaginella

• both are heterosporous
• megagametophyte (= nucellus) is reduced and retained on sporophyte
• megasporangium is surrounded by an integument
• ovule = megasporocyte (which gives rise to a megaspore) + nucellus + surrounding integument

Ovule becomes the seed

Seed = embryo + food + seed coat

Vocabulary

click here to go to introduction to gymnosperm vocabulary