Carolus Linnaeus - late 18thC
Species Plantarum 1753
Systems Naturae 1767
- (24) major categories of plants (Divisions)
- (23) vascular (Phanerogams);
- (1) non-vascular & vascular (Cryptogams)
K: Plantae - Ordovician - Non-vascular
- Silurian - Vascular
Continental Positions During
Early Plant Evolution
Vascular Plants - The Tracheophytes
• 1. Have specialized cell type for conducting water tracheids (early xylem tissue). Also has specialized cell
type for conducting sugar - seive cells (phloem tissue).
• 2. Lignin in xylem for rigid structural support.
• 3. A branching, independent sporophyte.
Vascular Plants - The Tracheophytes
Vascular Plants - The Tracheophytes
(300 mya)
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Non-seed Tracheophytes - haloid & diploid generations
totally independent
- spores most prominent resting state
Rhyniophyta - the earliest Tracheophytes
(extinct by Devonian Period 400 mya)
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1. Simple vascular system (xylem &
phloem) in stem.
2. “Leaves” flattened scales - no
vascular tissue.
3. No roots - but rhizomes.
4. Dichotomous stem branching.
5. Aerial branches and sporangia at
branch tips.
6. Spores were in groups of four (?)
tetrads - indicate meiosis
plant body - a sporophyte (2n)
spores - (n) ---> gameophyte (n)-->
sexual reproduction--> sporophyte (2n)
(fossil)
Lignier’s Hypothesis (1903)
How Roots Evolved from Stems
• ancestoral form --->
Evolution of Leaves
• Leaf - a flattened photosynthetic structure emerging from the stem and
possessing true vascular tissue.
• Probably evolved from sterile sporangia.
Evolution of Leaves
• Leaf - a flattened photosynthetic structure emerging from the stem and
possessing true vascular tissue.
• Complex leaves arose as photosynthetic tissue developed between
complex branching patterns
Homospory
The Most Primitive Spore Process
• one type of spore; one type of gametophyte
Heterospory
The Most Advanced Spore Process
• two types of spores; two types of gametophytes
• heterospory probably evloved several times
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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1. Leaves small and sessile; no ligule
at base.
2. Stems with aerial branches and
rhizomes; dichotomous branching.
3. Branch roots originate deep within
main root.
4. Mainly perennial.
5. Low growing in temperate forest or
epiphyte in Tropical forest.
6. Homosporous.
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• Plectostele - dissected xylem
• with phloem branches in
• between.
– Xylem - all tracheids.
– Phloem - all seive cells
• Epidermis - contains stomata.
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• Plectostele -
• Always a layer of parenchyma cells between xylem and phloem.
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• Plectostele - dissected xylem
• with phloem branches in
• between.
– Xylem - all tracheids.
– Phloem - all seive cells
– mucilaginous canal
• Epidermis - contains stomata.
• Exarch Stele -
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• A. Exarch Stele -
• B. Mesarch Stele
• C. Endarch Stele
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• Sexual Reproduction:
sporophyte (2n) ---- meiosis ---->
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• ------> spores (n) --> gametophyte (n) --> antheridia (n) & archegonia (n)
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(homospores)
• antheridium ----> sperms (n)
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-- fertilization --> zygote (2n) --> sporophyte (2n)
• Archegonium ----> egg (n)
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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• Sexual Reproduction:
sporophyte (2n) ---- meiosis ---->
• ------> spores (n) --> gametophyte (n) --> antheridia (n) & archegonia (n)
• antheridium ----> sperms (n)
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-- fertilization --> zygote (2n) --> sporophyte (2n)
• Archegonium ----> egg (n)
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
• MALE GAMETOPHYTE:
• Antheridia (n) on crown.
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Embedded (like Anthoceratophyta)
• Biflagellated sperms (n)
• FEMALE GAMETOPHYTE looks much the same.
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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strobilus (2n) -
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stem with short
internodes and fertile
appendages
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sporophyll (2n)
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sporangium (2n)
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spores (n)
K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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sporophyll & sporangium
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adaxial view
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K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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K: Plantae Div: Lycophyta
G: Lycopodium “ground pines”
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gemmae or bulbils (2n)
(asexual reproduction)
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axial sporophylls
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K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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Mainly in tropical areas
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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1. Herbaceous: perennial.
2. Ligulate* leaves; microphyllous; spirally or alternately arranged.
3. Abundant branching.
4. Some vessels* in xylem.
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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1. Herbaceous: perennial.
2. Ligulate*leaves; microphyllous; spirally or alternately arranged.
3. Abundant branching.
4. Some vessels* in xylem.
5. Strobilus composed of sporophylls each bearing a single sporangium
on the adaxial surface.
6. Heterosporous* reproduction.
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
• 6. Heterosporous* reproduction.
• Strobilus (2n) --> microsporophylls (2n) --> microsporangium (2n) -->
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megasporophylls (2n) --> megasporangium (2n) -->
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meiosis
• microsporangium (2n) --> microsporocytes (2n) ---------------> microspores (n)
• megasporangium (2n) --> (4) megasporocytes (2n) ----------> (4) megaspores (n)
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K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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meiosis
• microsporangium (2n) --> microsporocytes (2n) ---------------> microspores (n)
• megasporangium (2n) --> (4) megasporocytes (2n) ----------> (4) megaspores
(n)
• --> microspores (n) --> male gametophytes (n), antheridium --> sperms (n)
• --> (4) megaspores (n) --> female gametophytes (n), archegonium --> egg (n)
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dioecious
triradiate
walls -->
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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fertilization - -> zygote (2n) --> adult sporophyte (2n)
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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fertilization - -> zygote (2n) --> adult sporophyte (2n)
K: Plantae Div: Lycophyta
G: Selaginella “ground pines”
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K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
• 1. Quill-like leaves spirally attached to a corm; microphyllus and ligulate.
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Corm - thickened underground stem. Nodes very close together.
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Lacunae --->
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
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1. Quill-like leaves spirally attached to a corm; microphyllus and ligulate.
Corm - thickened underground stem. Nodes very close together.
2. Each leaf has 4 lacunae; stomata in epidermis. *
3. Some seive cells lack nucleus at maturity - plasmodesmata with adjacent
cells.
4. Stem and root protostelic.
5. Xylem consists of large numbers of parenchyma cells with few tracheids. *
6. Delicate roots grow from base of corm (rhizophores); stele bound by
well defined endodermis*; have root caps.
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
• 7. Heterosporous.
• 8. Every leaf of Isoetes is potential a sporophyll; per season •
sterile leaves 1st; then megasporophylls; then microsporophylls.
• --> 1 million microspores; 50 - -> 300 megaspores.
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
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Sporangium massive > 7mm.
Velum - covering over sporangium.
Trabecula - strands of sterile tissue extending from the sporangial wall.
Tapetum - innermost layer of the sporangial wall. Indistinguishable.
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
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meiosis
(all spores set free)
• microsporangium (2n) ---------> microspores (n) --> male gametophyte (n)
• megasporangium (2n) --------> megaspores (n) --> female gametophyte (n)
• male gametophyte (n) --> antheridium (4 sperms) multiflatelated
• female gametophyte (n) --> archegonium (1 egg)
• *further reduction of
• gametophyte!*
• colorless, saprophytic
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
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male gametophyte (n) --> antheridium (4 sperms)
female gametophyte (n) --> archegonium (1 egg)
*further reduction of
gametophyte!*
• colorless, saprophytic
• no suspensor
• 1 embryo develops
• from each gametophyte
K: Plantae Div: Lycophyta
G: Isoetes “quillworts”
• No suspensor; delayed development
• of the stem.
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