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Flowers
Floral Morphology
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Review structure of a flower
Floral terminology
Floral development
Angiosperm pollen
Inflorescences-how flowers borne on
the plant
@400 families, 365, 000 species
365,000 variations on a theme
We will only discuss a little of the
variation
Flower – a
determinate
stem tip
with modified
leaves
Sepal = leaf
Petal = leaf
Stamen = leaf
bearing
pollen sacs
Carpel = leaf
bearing ovules
(makes up pistil)
pistil
peduncle
All petals = corolla
All sepals = calyx
Calyx + corolla = perianth
/seeds
Pistil = stigma, style &
ovary
Gynoecium = all the carpels
Androecium = all stamens
Calyx = all the sepals
Corolla = all the petals
Stamen = filament & anther
Anther = 4 pollen sacs
Tepals = collective term used
when sepals & petals look
alike
Flower parts
Floral symmetry
Actinomorphic =
radially symmetrical
Zygomorphic =
bilaterally symmetrical
Zygomorphic flower
Actinomorphic flowers
Monocot flower
Flower parts in 3’s
or multiples of 3
3 petals
3 sepals
3, 6, 9 stamens
3 carpels
Tepals
Lilies – monocot
flowers
2 whorls of perianth
When the petals and sepals
have the same color and
morphology
Tepals
Lilium
flower bud
Petal
Typical
monocot
flower
with
parts
in
3’s
Tepals
Sepals
Monocot flower x.s.
Note: in this flower the sepals and petals often
look alike (colored) therefore = tepals
Anther x.s.
4 pollen sacs
Vascular
Bundle of
Connective
Dicot flower x.s. – flower parts in 4’s or 5’s
Carpels
• The units that contain the seeds
• Part of the ovary
• If the ovary has more than one carpel you usually
see more than one locule (chamber containing
seeds)
• You can sometimes tell how many carpels are in a
flower by looking at the tip of the style. Number of
style tips = number of carpels
• Carpels are leaves that have rolled up to enclose the
ovules. Later a number of these may have fused
together to form syncarpous ovaries (i.e., they
evolved from leaves)
• Note: stamens are also modified leaves with
attached pollen sacs
Magnolia
numerous flower parts
Magnolia carpels
Laminar stamens
Liriodendron tulipifera – tulip tree
Laminar stamens – leaf-like
Apocarpus gynoecium
Carpels free from each other and distinct
Syncarpus gynoecium
Fused carpels
Sympetalous corolla tube
Vinca minor
Fused petals
Insertion of floral structures
Hypanthium = cup-shaped extension of the floral
axis usually formed from the union of basal parts
of calyx, corolla, & androecium; commonly
surrounds or encloses the pistil(s).
Hypogynous--perianth & androecium inserted around base of gynoecium
Perigynous—perianth & stamens fused at base to form a hypanthium=
floral cup, that surrounds ovary but is free from it
Epigynous—hypanthium is fused to ovary such that the sepals, petals,
and stamens appear to be inserted in the top of the ovary
Perigynous
Superior ovary
Hypanthium
Prunus -- hypanthium
Vinca minor
sepal
Nectary
Vinca minor – Periwinkle
pollen
Bumble bee with long proboscis
Pollination
Placentation types – how the ovules are attached
Syncarpus ovary, axile placentation
5 fused carpels
Floral development
• Usually controlled by external
influences
• Day length – photoperiod
• Sometimes temperature controlled –
low temperatures
• Vernalization – germinating seed given
cold treatment to hasten flowering
• Apical meristem bearing leaves has an
altered mode of production of lateral
appendages-apex widens
Tomato floral apex
Apical meristem widens – as flower develops
apical meristem diminishes
Sepal primordia
Floral development is a
continuous series of
events-often there is a
rapid elongation of the
floral axis-especially in the
inflorescence axis
Periclinal divisions that form sepals and petals
are nearer the surface (more leaf- like) –
stamens develop from deeper layers
Carpel development – Horse-shoe stage
Carpel primordia develop by periclinal
divisions at the apex – followed by divisions
in adaxial direction – forms a horse-shoe
shaped structure– then upward growth
Anther dehiscence
Angiosperm pollen
Aperture = a specialized region of the wall
that is thinner than the rest
Monocolpate
Colpus = elongated aperture with a length/
width ratio greater than 2.
Monocolpate or monoporate
Single aperture– shapes differ here
Pore – circular or elliptical
Aperture
Tectate/collumellate angiosperm pollen wall structure
Exine –
sporopollenin
1. Tectum =roof
2. Columellaepillars or columns
3. Foot layer
Intine –
cellulose
Sculptural
elements
Tricolpate
Tricolporate
Triporate
e = equatorial view; p = polar view
Most common pollen types in eudicots
Angiosperm pollen grains
Monocolpate
Tricolpate
Triporate
Flower
Determinate stem
tip
Borne singly or
in
inflorescences
with
several flowers
Note: on these inflorescences, the largest flower (red circle) is the oldest, i.e., it was the 1st one to develop
Raceme = single axis with flowers on
pedicels attached to axis
Spikes = single axis, sessile flowers
Umbels
Compound umbel
Several flowers,
stalks all radiate
from one point
Head or capitulum - Asteraceae
Dense cluster of flowers without pedicels- disc
flowers in the center, ray flowers @ the outside
Panicle = compound inflorescence
containing spikes, racemes or corymbs
Corymb = broad inflorescence where
lower pedicels are longer, flowers all
at same level, terminal flower develops
last
Cyme
Flat-topped inflorescence,
Determinate, paniculate,
Terminal flower blooms first
Inflorescences
Self quiz – label the parts