The Wonderful World of
Green Plant Diversity and
Evolution
Biol 366
Spring 2012
Tree of Life: The Big Picture
now Bacteria
Archaea
Eukaryotes
>2 bya
>3.5 bya
ca. 4 bya
membrane-bound
nucleus, organelles,
etc.
Fig. 1.1 from Simpson
Green plants share:
• Chlorophylls a (ancestral) and b
• Starch storage
• Stellate flagellar structure
• Certain gene transfers from the chloroplast to the
nucleus
• And other features (see Ch. 3)
Green plant diversity:
• Ca. 350,000 species
• Two major groups: 1) chlorophytes
(marine and other green algae) and 2)
streptophytes [freshwater green algae
and embryophytes (= land plants)]
• A major branch (clade) in the
eukaryotic Tree of Life
Fig. 3.1 from Simpson
Some definitions
• Clade = branch on an evolutionary tree,
a lineage, includes an ancestor and all
its descendants. Ex.: Green plants,
chlorophytes, land plants.
• Paraphyletic group = a group that
includes an ancestor and some (but not
all) of its descendants, indicated by
double quotation marks. Ex.: “Green
algae”
Chlorophytes
Fig. 3.1 from Simpson
Spirogyra
Chara
Nitella
(Judd et al. 2008)
Basal streptophytes
desmids
haploid body
Conjugation in
Spirogyra
Haplontic life cycle
(haploid dominant
or zygotic meiosis)
The only diploid cell
Is the zygote
zygote (2n)
biology.unm.edu
♀
Charales
Haplontic but some have
multicellular gametangia
(gamete-producing structures)
♂
mason.gmu.edu
Embryophytes (land plants)
share:
• Cuticle
• Alternation of generations (multicellular
sporophyte and multicellular gametophyte)
• Multicellular gametangia (gamete-producing
structures)
• Multicellular sporangium (spore-producing
structure)
• Embryo (young sporophyte)
• Parenchyma? (more likely ancestral)
Generalized embryophyte life cycle:
Alternation of generations
Bryophytes
• Hornworts, liverworts, mosses
• Gametophyte-dominant
• No vascular tissue (except conducting
cells in a few mosses)
• Separate male and female
gametophytes
• Sperm must swim to the egg, therefore
need water for fertilization and
therefore must remain small
liverworts
mosses
hornworts
Plant Tree of Life: Embryophtes
“Bryophytes”
now
Liverworts
ca. 450 mya
Hornworts
Mosses
Tracheophytes
(vascular plants)
Liverwort gametophyte
Liverwort
thallus showing
air pores
Liverwort
Multicellular gametangia
(male = antheridia)
Liverwort
Multicellular gametangia
(female = archegonia)
Oogamy
Retention of zygote within the
female gametophyte
Multicellular embryo
G
S
Hornworts
Moss male gametangia
(= antheridia)
Capsule = sporangium
of the sporophyte
Generalized embryophyte life cycle:
Alternation of generations
Tracheophytes (vascular plants)
• Vascular tissue (tracheids) present
• Include lycophytes (quillworts, clubmosses,
spikemosses), monilophytes (ferns,
horsetails, whisk ferns), and spermatophytes
(seed plants)
Fig. 4.1 from Simpson
Lycophytes & Monilophytes
• Quillworts, clubmosses & spikemosses (=
lycophytes); ferns, whisk-ferns, & horsetails
(= monilophytes);
• Independent gametophytes and sporophytes
• Sperm must still swim to the egg
• Most are homosporous; a few evolved
heterospory
• Many homosporous ferns have means of
avoiding self-fertilization
Lycophytes
Isoetes (quillwort)
Lycopodium
and friends
(clubmosses)
Selaginella (spikemoss)
Monilophytes
(ferns, horsetails, whisk ferns)
horsetails
Whisk-fern (Psilotum)
Ferns (Leptosporangia)
Nutritionally independent
sporophytes and
2n
gametophytes
sporophyte
2n
gametophyte
1n
1n spores
2n
2n
Fern Life
Cycle,
Fig. 4.32,
Simpson
Lignophytes (woody plants) &
Spermatophytes (seed plants)
• Secondary xylem (wood) & bark,
heterospory, seeds, eustele, pollen (also
pollen tube, pollination droplet)
• Includes gymnosperms and angiosperms
Fig. 5.1 from Simpson
Gymnosperms
• Conifers, gingko, cycads, Gnetales
• Molecular data support this group as having
a single common ancestor
• No obvious defining character (see
characters for Lignophytes &
Spermatophytes)
Female cone with each scale
bearing usually two ovules;
directly exposed to pollen
Male cones with each
scale bearing two or
more microsporangia
male
pine pollen
pine microsporangia
biology.ualberta.edu
female
Fig. 5.7
from
Simpson
Angiosperms
•
•
•
•
•
“Dicotyledons”, monocotyledons
Heterosporous (ancestral)
Sporophyte-dominant (ancestral)
Pollen = male gametophyte (ancestral)
Archegonia lost; embryo sac = female
gametophyte; ovules enclosed in
carpels (indirect pollination)
• Double fertilization produces zygote +
primary endosperm nucleus
Flower = a short, determinate shoot bearing highly
modified leaves, some of which are fertile (i.e.,
bearing either microsporangia or megasporangia),
with the megasporangia in carpels
Animal pollination syndromes
Wind pollination
A wide range of fruit types…
Fig. 5.7
from
Simpson
The wonderful world of land plant diversity
over 300,000 species
of angiosperms