Chapter 4: Evolution and Diversity of Vascular Plants

Michael G. Simpson

Vascular Plants = Tracheophyta (Tracheophytes)

Apomorphies?

Alternation of Generations: Haploid (n) & Diploid (2n) adult phases

“Bryophytes”: Gametophyte dominant, long-lived

Bryophytes (Liverworts, Hornworts, Mosses): Gametophytes are dominant, long-lived

Alternation of Generations: Haploid (n) & Diploid (2n) adult phases

Vascular Plants: Sporophyte dominant, long-lived

Vascular Plants: Sporophytes are dominant

Rhynia

Sporophytic axes branched with

multiple sporangia

Two early branching patterns in vascular plants:

lignin - hard substance secreted within secondary cell wall

Major adaptive:added structural support enabled

vascular plants to grow much larger.

secondary cell wall

- forms between 1˚ cell wall and plasma membrane in some plant cells

- adds structural support

- found in tracheids, vessels, fibers (all dead cells)

lignified secondary cell wall

Sclerenchyma

1) Secondary cell wall (+ primary)

2) Dead at maturity (usually)

Fibers

Elongate, sharply tapering

Sclerenchyma

1) Secondary cell wall (+ primary)

2) Dead at maturity (usually)

Sclereids

Isodiametric to irregular

Tracheary elements1) cells that function in water/mineral conduction2) cells dead at maturity, with lignified, 2˚ cell walls3) cells arranged end-to-end, forming long tubes

Xylem = tissue composed of:

1)tracheary elements

2)parenchyma

3)fibers

(These have common origin/location/function.)

Tracheary ElementsTracheids – imperforate (only pits at end walls). Found in

most monilophytes (except Equisetum and some lepto. ferns) and most gymnosperms (except Gnetales)

Vessels – perforation plates = holes in end walls. Evolved independently from preexisting tracheids in Equisetum, a few leptosporangiate ferns, all Gnetales, and almost all angiosperms

Sieve Elements

Sieve cells – only sieve areas Sieve tube members - Sieve plates

All vasc. pls. except angiosperms Apomorphy of Angiosperms

-cells with sieve areas/plates, having pores lined by callose

callose (polysaccharide composed of β-1,3-glucose units) -lines pores of sieve areas!

Phloem

= tissue composed of:

1)sieve elements

2)parenchyma

3)fibers

These have common origin/function.

Casparian Strip: forces fluids from outside through plasma membrane = selective absorption

Endodermis – single layer of cells surrounding vasculature of roots and some underground stems.

Rhynia- one of earliest

vascular plants(ca. 400 million years

ago)

- lacked roots

Roots

Function in anchoring and absorption.

Root

apical meristem- region of actively

dividing cells

RootsFive diagnostic features:

1) Root cap – functions to protect apical meristem and lubricate root during growth.

2) Root hairs – function to greatly increase water/mineral absorption (exception Psilotopsida).

3) Central vascular cylinder – site of conduction of water/minerals and sugars.

4) Endodermis – Casparian strip functions in selective absorption.

5) Endogenous lateral roots – develop from pericycle or endodermis, penetrate to outside.

Mycorrhizae

Symbiotic association with various species of fungi.

Found in many, if not most, vascular plants.

Fungus aids plant by

1) increasing surface area for water and mineral absorption

2) increasing efficiency of mineral absorption.

Fungus benefits in obtaining photosynthates (sugars and other nutrients) from the plant.

Tracheophyta – Classification

Lycopodiophyta – lycophytes

Apomorphies: 1)Roots dichopodial

-apical meristem may branch into two.

2) Root protoxylem endarch (to inside)

Protoxylem – first xylem formedMetaxylem – later xylem

3) Stem protoxylem exarch (to outside)

4) Sporangia dorsiventral (flattened upper and lower surfaces)

with transverse dehiscence.

Shoot = stem + leaves

Leaf – sporophytic

Lycophyll – simple leaf with 1 vein, no leaf gaps.

Tracheophyta – Classification

LYCOPODIOPSIDA

Lycopodiaceae

homosporous = 1 type of spore

5 genera: Huperzia, Lycopodiella, Lycopodium,

Pseudolycopodiella, Phylloglossum)

Lycopodium digitatum

Ligule – tiny appendages on upper side of leaf (near base)

ISOETOPSIDA

Selaginellaceae + Isoetaceae

1) Leaves ligulate

2) Heterosporous – 2 types of spores

Heterospory – two types of spores:

megaspores (from megasporangia)

microspores (from microsporangia)

Isoetes – quillwort/Merlin’s grass

Isoetaceae

Quillwort family

1 genus:

Isoetes (ca. 200 spp.)

Lycopods native to San Diego area:

Isoetes Merlin’s Grass

Isoetes orcuttii

Isoetes howellii

Selaginella

spike-moss

Selaginellaceae

Spike-moss family

1 genus:

Sellaginella (700 spp.)

Selaginella bigelovii

Selaginella cinerascens

Some Selaginella

have dimorphic

leaves

Selaginella apoda

2 rows large leaves

Selaginella apoda

2 rows small leaves

Some Selaginella

have dimorphic

leaves

Lepidodendron

Extinct Lycopods were tall trees:

make up some of coal deposits

Euphyllophyta

Apomorphies:1) roots monopodial2) root protoxylem exarch3) sporangia terminal on lateral branches, longitudinally dehiscent

Archeopteris

Euphyllophyta

Apomorphies:1) roots monopodial2) root protoxylem exarch3) sporangia terminal on lateral branches, longitudinally dehiscent4) shoot with euphylls

shoot = stem + leaves

Euphyllophyta

Apomorphies:1) roots monopodial2) root protoxylem exarch3) sporangia terminal on lateral branches, longitudinally dehiscent4) shoot with euphylls

Leaves of euphyllophytes:a)evolved by planation & webbing of stemsb)have multiple veinsc)have a leaf gap – parenchyma replaces vascular tissue upper junction of leaf trace with stem vasculature

Euphyllophyta

Apomorphies:1) roots monopodial2) root protoxylem exarch3) sporangia terminal on lateral branches, longitudinally dehiscent4) shoot with euphylls5) 30 kb chloroplast DNA inversion

Tracheophyta – Classification

Monilophyta-monilophytes

Apomorphies:1) stem protoxylem     mesarch2) siphonostele

Equisetopsida(Equisetophytes)

EquisetaceaeEquisetum

Horsetails / Scouring Rushes

Equisetopsida

Apomorphies:1) stem ribbed with canals2) leaves reduced, whorled

Equisetopsida

Apomorphies:1) stem ribbed with canals2) leaves reduced, whorled3) sporangiophore4) spores with elaters, chlorophyllous

Equisetum hyemale common scouring-rush Equisetum laevigatum smooth scouring-rush

whorled microphylls

cone(strobilus)

Subgenus Hippochaete – souring-rushes

Equisetum arvense Common Horsetail

Subgenus Equisetum – horsetails

Calamites

-fossil (extinct) equisetophyte,

was tree-sized, makes up coal deposits today

Psilotopsida

Apomorphies:1) Roots unbranched, root hairs absent.2) Gametophyte subterranean, mycorrhizal.

Psilotopsida

Two members:

1) Ophioglossales ophioglossoid ferns

2) Psilotales whisk ferns

Ophioglossales:

One family: Ophioglossaceae

4 genera, incl. Botrychium, Ophioglossum

Ophioglossaceae

Ophioglossum californicum Calif. Adder’s Tongue

Psilotales

Apomorphies:

1) Roots lost.

2) Leaves reduced (microphylls or enations).

3) Synangium with bifid appendage.

Psilotales

One family:

Psilotaceae

2 genera:

Psilotum

Tmesipteris

Psilotum nudum

dichotomous branching

enations / microphylls

Psilotum nudum

Psilotum nudum

synangium

bifid(2-forked)appendage

Marattiopsida

Marattioid Ferns

Apomorphy:

1) Polycyclicsiphonostele

Marattiaceae

eusporangia

PolypodiopsidaLeptosporangiate Ferns

Apomorphy:Leptosporangium

PolypodiopsidaLeptosporangium:

- one cell thick

- spores ejected

Stem:

rhizome

trunk

vine

fern leaves can have specialized terminology:

leaf = frond

petiole = stipe

major divisions = pinna (1˚, 2˚, etc.)

ultimate divisions = pinnules

fern leaf venation:

open (simple or forked), reticulate

fern scales:

e.g., clathrate or non-clathrate

sorus (pl. sori) – aggregation of sporangia

indusium - flap

shape /

morphology

leptosporangium / annulus

-varies with different groups/families

egg

sperm

Fern leaf development: circinate

fiddle head - crozier

Salviniales

Apomorphies:1) aquatic adaptation

2) heterospory (independently evolved)

3) sporocarps (dormant, seed-like body, house specialized sporangia)

Two famlies:Marsileaceae – clover fern family

Salviniaceae – floating fern family

Marsilea Salvinia Azolla

Marsileaceae

Marsilea

Pilularia

Salviniaceae

Azolla

Salvinia

Azolla Mosquito Fern

- symbiotic relationship with blue green bacteria; “seeded” in rice paddies for nitrogen fixation

- inhibits mosquito population by covering surface

- fodder for animals

Cyatheales:

Cyatheaceae

largest family of tree ferns

(trunk arborescent)

Cyathium

a tree fern

Aspleniaceae

-linear sori / indusia

Polypodiales:

A few families:

Polypodiaceae

- sori exindusiate (“naked)

Polypodium californicum California Polypody

Polypodiaceae:sorus

exindusiate

Platycerium Staghorn Fern

sporangia “acrostichoid” (not aggregated

into sori)

Polypodiaceae

Pteridaceae

-false indusium

Cyathium

a tree fern

Adiantum reniformis

California Maidenhair FernPteridaceae