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Seed Plants I: Seed Plants Without Flowers ("Gymnosperms") -…
Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")
Division Progymnospermophyta: Progymnosperms
Archaeopterides
Characteristics include
stems had a siphonostele pith surrounded by a ring of primary xylem bundles
reproduction was heterosporous
tall trees with abundant wood and secondary phloem
both megaspores and microspores were produced in its own distinctive sporangium
more derived progymnosperm
Archaeopteris in the order Archaeopteridales
seeds were not produced
Evolution of Seeds
earliest known progymnosperm species with heterospory is Chauleria
began producing pollen chambers and evolving into pollen grains
resulted in four types of pollen that had become common
Aneurophytales
characteristics include
all had a vascular cambium and secondary growth
primary xylem of their stems was a protostele
vary in stature, can be shrubs or tall trees
had little webbing between their ultimate branches
contains more relictual progymnosperms
Proteokalon
Tetraxylopteris
Protopteridium
Triloboxylon
Aneurophyton
Eospermatopteris
Division Pteridospermophyta: Seed Ferns
Pteridospermophyta
ring of vascular bundles surrounding a pith
had a long-lived vascular cambium that produced both xylem and phloem
Tracheids were long and wide
seed ferns, all extinct
they were any woody plant with fern-like foliage that bore seeds instead of sori on its leaves
Division Coniferophyta: Conifers
characteristics include
diverse with approximately 50 genera and 550 species
always simple needles or scales
never vines, herbs, or annuals, and they never have bulbs or rhizomes
leaves are mostly perennials and persist for many years
most are trees of gigantic size such as redwoods
venation of conifer leaves are often simple, with just one or two long veins running down the center of a needle-shaped leaf or several parallel veins in scale-shaped leaves
leaf veins have endodermis and a tissue called transfusion tissue
consists of transfusion parenchyma cells and transfusion tracheids
all have pollen cones and seed cones, most of which are woody
Division Cycadophyta: Cycads
characteristics include
stout trunks with pinnately compound leaves
most are short but can reach great heights
trunk is covered in bark and persistent leaf bases
thick cortex containing secretory ducts surrounding a small amount of manoxylic wood
tracheids are long and wide and rays are massive
9 or 10 genera and approximately 100 species
Division Cycadeoidophyta: Cycadeoids
characteristics include
individual cones contained both microsporophylls and megasporophylls
each ovule had a stalk
had vegetative features very similar to those of cycads
between ovules were thick, fleshy scales
all extinct
Division Ginkgophyta: Maidenhair Tree
contains single living species, Ginkgo biloba
have both short shoots and long shoots
broad leaves but have dichotomously branches veins like seed ferns
cones are not produced
wood like that of conifers by lacking vessels and axial parenchyma
ovules occur in pairs at the ends of short stalks
stout trunk and many branches
pollen is produced
Division Gnetophyta
contains 3 groups of enigmatic plants:
Ephedra with 40 species
tough shrubs and bushes that are common in desert regions
leaves are reduced and scale like
Welwitschia mirabilis the only genus in the species
only exist in deserts of South Africa or in cultivation
have short, wide stem and only two leaves
Gnetum with 30 species
mostly vines or small shrubs with broad leaves similar to dicots
