Plant taxonomy Flashcards
what are in the spermophytes
gymnosperms and angiosperms
developed pollen
seeds have seed coats to confer ability to store starch and proteins and defenses as well as confers dormancy.
What sex are plants
All land plants are haplodiplontic= This means generations span two multi-cellular individuals – one haploid and one diploid.
The diploid generation is called the sporophyte
The haploid generation is called the gametophyte - this stage
produces gametes by mitosis.
When did land plants evolve?
What are the first land fossils?
In early Ordovician from multi-cellular freshwater algae
First land fossils (472 Ma) are liverwort cryptospores
Liverworts and other bryophytes dominated early terrestrial life
What are Bryophytes
Non-tracheophytes – i.e. poorly developed vascular system limits stature.
First plants to evolve mycorrhizal affiliations
Distributed widely but…gametophyte-dominated life cycle requires water for reproduction
Explain bryophyte Sex
The haploid gametophyte occupies more of the
bryophyte life cycle than for vascular plants
The free-living photosynthetic plant you see is the
gametophyte
What are the 3 different clades of Bryophytes
*Liverworts - Marchantiophyta
-deeply lobed or segmented ‘thalloid or foliose’ leaves arranged in three ranks; lack differentiated stem & leaves – 9,000 species
*Mosses - Bryophyta
-variable stem form with simple leaves; threadlike rhizoids for
anchorage only – 12,000 species
*Hornworts - Anthocerotophyta
-thalloid leaves; tall, narrow sporophytes growing continuously from a near-basal meristem – 100 species
What happened in the devonian period and what are the key features
Key Features
Lignification & Vascular tissues allow plants to grow larger
Roots allowed deeper soil penetration, nutrient access & structural support
First vascular plant fossils (spores) appear late Ordovician, but land plants underwent rapid radiation during Devonian (415-360 Ma)
Lycopodiophyta (Club Mosses)
Tracheid-based vascular tissues, but lack vascularised leaves
Currently about 1200 species
Sporophyte stage dominant
30m tall plants dominated Carboniferous
forests 310Ma
Pterophytes (Ferns)
ferns are tracheophytes & first plants to evolve true vascular leaves –plants grow from a rhizome
Two groups
Sporangia of Eusporangiate ferns arise from several epidermal cells, unlike Leptosporangiate ferns
(sporangia arise from a single cell)
Fern Sex
The conspicuous diploid sporophyte occupies most of the
Pterophyte life cycle The small, free-living gametophyte is
photosynthetic.
What are the three extant classes of Eusporangiate ferns
Whisk ferns - Psilotopsida,Tropical - lack differentiated leaves & roots (lost after divergence from other ferns) – 90 species. Long green and stringy.
‘Tropical Ferns’ - Marattiopsida
Fleshy roots and very large fronds – 150 species
Important
Horsetails - Equisetopsida are Wiry or Scale-like leaves radiate in a whorl from a jointed photosynthetic stem – 15 species
Leptosporangiate ferns
True-Ferns - Polypodiopsida (often) compound leaves (fronds) created as ‘fiddleheads’ (croziers) uncurl; sporangia on lower leaf surface in clusters (sori) – 11,000 species
Variety of growth-forms.
Tree-ferns - up to 24m tall
Epiphytic
Aquatic
What are the two of the seven Orders of Ferns most common in britain?
Polypodiaceae
Sori arranged in round/oblong clusters; usually lack
indusium. Scaly, creeping rhizomes.
Aspleniaceae
Sori arranged in lines and covered by a flap-like
membrane (Indusium)
Spermatophyte timeline
Progymnosperms evolved 390 Ma but true
gymnosperms radiated in Permian and dominated
early Mesozoic – some evidence of pollination by
scorpionflies in Jurassic
Angiosperms appear in Jurassic & have dominated
since Cretaceous – over 300,000 extant species
Now extinct (Pteridospermatophyta) ‘Seed ferns’
were first major group and dominated the late
Palaeozoic
Seedy Sex
Spores are retained by the (large) sporophyte to
produce (small) haploid gametophytes.
Pollen is the male gametophyte
and produces sperm – this is transferred from the plant
The female gametophyte (egg) develops inside the ovule and is
retained on the parent plant.
Gymnosperms
Characterised by seeds that develop on surface of scales or leaves (often modified to form cones)
Includes largest and oldest living plants
Coast redwood (Sequoia sempervirens) grows to 112m; bristlecone pine (Pinus aristata) lives to 5,000 years.
What are the four subclasses Gymnosperms
*Gnetidae
Vascular tissues possess ‘vessel elements’ – 70 species (Ephedra only European genus)
*Ginko - Ginkoidae
Fan-shaped leaves with dichotomous veins radiating out into leaf blade – 1 species (China)
*Cycads - Cycadidae
Stout, woody trunk with crown of large, stiff (palm-like) leaves;
dioecious – 300 species (none in Europe)
*Conifers - Pinidae
Resinous trees or shrubs; ‘evergreen’ scale- or needle-like leaves; monoecious – 600 species (3 Families in Europe)
Europaean Pinidae
*Cupressaceae – Cypress family
Leaves linear or scale-like; pollen cones small, terminal; scales on seed
cones heavily reduced, consist of bracts with 1 to many seeds
*Taxaceae – Yew family
Seeds surrounded by fleshy aril
Pinaceae – Pine family
Leaves in clusters (fascicles) surrounded by sheath, or spiral on long or short shoots; pollen cones axillary; woody scaled seed cones each with 2 seeds
Angiosperms
Obvious distinguishing feature is the flower
Carpel encloses the ovules – permits specialised
pollination syndromes & reduces self-pollination
Seeds also protected by carpel (thickens to fruit) &
endosperm provides early embryo nutrition
Vessel elements allow more efficient water transport
through xylem (see Gnetidae)
Cretaceous Explosion
(angiosperms)
A Whole Genome Duplication event happened to
plants 2 or 3 times in the Jurassic/Cretaceous
WGD - a doubling of a single species genome, or a
combination of genomes from two different species
‘Genetically diverse’ ancestor gives rise to new
lineage. birds and mammals increased aswell
Angiosperm Morphology
First approximation – separate into two structural
forms; Monocots and Eudicots
Monocots are named for the single cotyledon apparent shortly
after germination.
parellel veins
flower parts in multiples of 3
Roots Fibrous or rhizomes/bulbs
Vascular bundles are Complex
Dicots have two cotyledons.
network of veins
flower parts of multiples of 4 or 5
roots taproots
Vascular bundles arranged in a ring
Root form and function
Anchor the plant into the soil,
absorb minerals, water, and store food
Shoot Morphology
Shoots consist of a stem, leaves, flowers
and fruits
describe Stems
The terminal bud develops at the tip of the shoot
Alternation of nodes (points at which leaves are attached), and
internodes - stem segments between nodes
In the angle between each leaf and the stem, is an axillary
(lateral) bud, an embryonic side shoot
Leaves
Petiole is variable in shape; but generally consist of a flat blade and a stalk – the petiole - joining the leaf to the stem node
Leafless plants photosynthesise via stems or modified petioles - phyllodes
Most monocots lack petioles – instead the leaf base forms a sheath that envelops the stem (e.g grasses)
What are the two types of leaf shapes?
compound=made of small leaflets
entire
there are;
linear
rhomboid
spoon-shaped
Flowers
Evolved from compressed shoots with four whorls of modified leaves separated by very short internodes
Consist of four organs - in sequence from the outside to inside of the flower these are:
Sepals, Petals, Stamens, Carpels (female)
Receptacle & Calyx
At the apex of the flower stalk is a swelling - the receptacle - to which the flower parts are attached
The outermost whorl - the calyx - comprises a number
of leaf-like structures - sepals - these protect the
inner parts of the flower during the bud stage
The Corolla
Within the calyx, the next whorl - the corolla - is
comprised of (coloured) leaf-like petals
wind pollinated species have inconspicuous flowers
The Perianth
the calyx (sepals) and the corolla (petals)
together form the perianth
Sometimes sepals & petals are identical in
form and colour - so we count perianth segments (tepals)
What are the different tube like structures in sepals and petals?
Petals are sometimes joined to form a corolla tube
Sepals are sometimes joined to form a calyx tube
Flower Symmetry (dicots)
In zygomorphs the flowers are only symmetric about
one axis
In actinomorphs, sepals and petals are so arranged that they display radial symmetry
The Male Sex parts
The anthers contain the pollen sacs
The stamens consist of a stalk (filament) and a head (anther)
The Female Sex parts and Ovary Positions
At the base of the carpel is the ovary (contains ovules)
Above the ovary is the stalk-like style (this can be single
or multiple)
At the tip of the style is the stigma – the receptive surface for pollen
A superior ovary is attached to the receptacle above the
corolla whorl and stamens (inside flower)
An inferior ovary has the calyx and corolla arising from the
top
Flowers can be either…?
solitary or multiple (inflorescence instead of flower)
Inflorescence Types I
(Elongated)
*Cyme – terminal flower opens first, followed in succession by lateral flowers from bract axils
*Panicle – a branched raceme
*Raceme – stalked lower flowers open first followed
sequentially upwards
*Spike – an unbranched Raceme; flowers stalk-less
Inflorescence Types II
(Flat-tops)
*Umbel – flower stalks of even length, all emerge from same point
*Corymb – stalks of outer flowers longer than inner to give appearance of flat top
*Head – crowded clusters of flowrs from commonnstalk
Asteraceae (inflorescence)
‘miniaturized’ flowers are grouped in a tight head or
Capitulum
The centre of the capitulum has disc florets
Ray florets line the outside, giving the appearance of petals
