Transcript Clematis

Flower - Structure and
organogenesis
Scott Russell
Office: 210 NML / Lab:143 GLCH
Phone: 325-4391 (office) 325-6234 (lab)
[email protected]
Morphological nature of the flower
• Flower is a determinate bisexual
shoot of appendicular reproductive
organs and associated floral
components
– Pedicel/receptacle represent a
determinate stem
– Floral components
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Sepals (collectively, calyx)
Petals (collectively, corolla)
Stamens (collectively, androecium)
Carpels (collectively, gynoecium)
• Floral components have been
subject to considerable modification
– Fusion
• Congenital or postgenital
• Adnation or connation
– Elaboration
– Various functional adaptations, often
in association with pollination
mechanisms
• Classical theory: philosophical basis of modern thought
about homologies of flowers date to Goethe’s ideas
– Flower is homologous to vegetative shoot. Evidence is from
serial homology
• Floral parts are appendicular
• Develop with specific venation patterns
• Can be compared in structure, evolution and development with
leaves
• Most ancient members of phylogeny are least adherent to the
general ideas
• Esau’s careful statement:
“The concept that leaves of the type found in ferns, gymnosperms and
angiosperms (megaphylls) have evolved from branch systems (see also telome
theory) has given rise to the speculation that, in their parallel evolution, leaves
and floral parts diverged before their leaflike form emerged. Nonetheless, in their
initiation, ontogeny, and basic vascular organization the parts of the less
specialized flowers show considerable similarity to leaves”
• Thus, divergent data also exist that may call this into question in
some plants. The effects of evolutionary modification on ancestral
form cannot be underestimated in its ability to obscure some of
these basal relationships.
Floral parts
• From outer whorls to inner, appendages are initially leaflike, but increasingly less so to the interior
– Sepals
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Often green, photosynthetic
Varying complexity and thickness
Epidermal organization often leaflike
Three-trace, unilacunar nodal anatomy
– Petals
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Usually pigmented and non-green, non-photosynthetic
Varying in thickness but simple in organization
Epidermal organization often with intricate cell boundaries
One-trace, unilacunar nodal anatomy
Floral parts, continued
– Androecium
• Consists of filament and stamen (with anther sac)
• Varying leaflike qualities
– Laminar is most leaflike
– Sterile forms in fertile flowers may be quite leaflike: staminodes
• Variability in stamen form from leaflike to essentially fused
microsporangia and little more
– Variable methods of anthesis (opening)
– Variable degrees of fusion (usually initiated as four, but often
fusing to form two locules)
– Variable numbers of pollen grains produced (usually closely
related with pollination syndrome – wind pollination usually
involves greatest production of pollen)
• One-trace, unilacunar nodal anatomy
Origin of primordia on the floral apex
Nodal anatomy of sepals and petals
Gifford and Foster 1989, Figs. 19-34, 19-38
Anther dehiscence & filament attachment
Anther dehiscence. A-D Longitudinal valvate dehiscence; E transverse
dehiscence; F valvular flaps; G apical pores
 Filament attachment
H Basal attachment of filament
I Versatile attachment of filament – attached at
middle, allowing free movement in the wind
Gifford and Foster 1989, Fig. 19-43
Putative primitive stamens
Gifford and Foster 1989, Fig. 19-43
Floral parts, continued
– Gynoecium
• Consists of carpel as the unit of organization
– Carpel is differentiated into stigma, style, ovary (containing
ovules)
• Gynoecium may consist of one or more carpels
• Multiple carpels may be simple or compound (fused)
– Fusion may be congenital (from initiation) or postgenital (later)
– Fused carpels are rarely totally fused; usually stigma retains its
lobed structure
• Carpels may be more, or less, leaflike depending on derivation
• Placentation – placement of ovules
– Laminar or marginal is considered ancestral
• Three-trace, unilacunar nodal anatomy
– Medial or dorsal trace occurs on abaxial side of carpel
– Lateral traces occur near the perimeter of the edge of the carpel
Nodal anatomy of stamens and carpels
Gifford and Foster 1989, Fig. 19-34
Variations in carpel structure
Position and Placentation
Carpel structure and fusion
Uniovulate carpels in A-C. (A) folded carpel with laminar placentation; (B) folded with
reduced margins; (C) involuted carpel formation. (D) Fusion of two carpels with parietal
placentation forming septum as in Brassicaceae. (Esau, Fig. 20.3).
Placentation
Gifford and Foster 1989, Figs. 19-33
Ovule orientation
Gifford and Foster 1989, Fig. 20-9
Flower Types
Superior ovary
Inferior ovary
Gifford and Foster 1989, Figs. 19-32
Opuntia flower
From Esau, Fig. 20.9
Floral anatomy of Lycopersicum, Ribes & Prunus
• Superior versus inferior ovary
• Differing forms of adnation, connation
A, C Lycopersicum; B, D Ribes; right: Prunus
Esau Figs. 20.5 and 20.7
Floral anatomy of Prunus
Esau Fig. 20.8
Primitive carpels
Or just pretenders…?
Degeneria carpels
Gifford and Foster 1989, Figs. 19-46, 19-47
Tasmannia fertilization
Gifford and Foster 1989, Fig. 19-43
Floral development
Grass variants
Butomus
From Esau, Fig. 20.13
Grass flower (idealized)
From Esau, Fig. 20.13
A-D Triticum, E Butomus
Esau, Fig. 20.15
Floral development
Clematis shoot apex and
derivatives
Clematis developing flower – stage II - tepals
Photo: Judy Jernstedt from BSA site
Clematis developing flower – stage III - stamens
Photo: Judy Jernstedt from BSA site
Clematis developing flower – stage IV – beginning of carpel initiation
Photo: Judy Jernstedt from BSA site
Clematis developing flower – stage IV – young carpels
Photo: Judy Jernstedt from BSA site
Clematis developing flower – stage V – developing carpels
Photo: Judy Jernstedt from BSA site
Clematis developing flower – stage V – close-up – carpel development
Photo: Judy Jernstedt from BSA site
Inflorescence Development
Helianthus head (sunflower)
Transition from vegetative
Broadening of shoot apex
Formation of floret primordia
Floret primordia
Floret differentiation