Download Lecture 3 – Floral Morphology

Lecture 3 – Floral Morphology
2 major phylogenetic/ developmental theories on origin of flower
•
Euanthial hypothesis (Arber & Parkin 1907):
Flower is derived from a uniaxial cone (cone with one axis)
i.e., a central axis with spirally attached fertile & sterile modified leaves
(sporophylls & bracts
Ø Angiosperm flower is equivalent to simple gymnosperm strobilus (or cone), as in
Cycads and the extinct Bennettitales
Ø superficially strobilar flowers (e.g. Magnoliales) viewed as primitive – Large,
radially symmetrical, numerous free & spirally arranged flower parts of foliar
origin (incl. laminar stamens, multiovular leaf-like carpels), large seeds
•
Pseudanthial hypothesis (Von Wettstein 1901; 1907):
Flower derived from pluriaxial cone (cone with multiple axes)
i.e., a central axis with numerous secondary axes, each bearing fertile or sterile
parts
Ø Angiosperm flower is equivalent to cones of conifers, Gnetales & the extinct
Cordaitales
Ø Current uniaxial angiosperm flower derived by aggregation and condensation of
a gymnosperm “inflorescence”
Ø Primitive flower is a compilation of small, simple, unisexual units on several
orders of axes, with a whorl of bract-like structures (“perianth”) at base. Bracts
on other axes now lost. Small simple carpels with one to a few ovules
Ø Piperales and “amentiferous” taxa (incl. Fagales) would thus be primitive.
Ø Latter is contradicted by fossil record
REVIEW OF BASIC TERMINOLOGY –
FLORAL WHORLS –
Sepals (outer perianth whorl)
à
Petals (inner perianth whorl)
à
…. Tepals (perianth parts look alike)
Stamens
Carpels
Collective names
CALYX
COROLLA
ANDROECIUM
GYNOECIUM
Perianth = Floral envelope (all sepals, petals or tepals)
Carpel: a simple pistil formed by one modified leaf (megasporophyll)
… or that part of a compound pistil formed by one modified leaf.
PISTIL = stigma, style plus ovary… megasporphyll
STAMEN = Filament plus anthers… microsporophyll
Locule: The chamber or cavity of an ovary containing the ovules
Nectary: glandular tissue on the flower (or elsewhere) producing nectary
Pedicel: Stalk of a single flower in an inflorescence
Peduncle: Stalk of a solitary flower of the entire inflorescence
Receptacle: Portion of the pedicel on which the flower parts are borne
[In composites (Asteraceae) refers to the part of the peduncle where the flowers of
the head are borne]
________________
Floral Diagram (e.g. Judd et al. p. 193) -- see handout
Floral Formula – see Judd et al. page 57
NUMBERS OF FLORAL PARTS
COMPLETE – With all the parts belonging to a typical flower (petals, sepals – or
tepals – stamens, pistil)
INCOMPLETE – Lacking one of the whorls
ASEPALOUS – lacking sepals
APETALOUS – lacking petals
IMPERFECT – Unisexual flowers (pistillate or staminate)
Imperfect flowers are also incomplete, by definition!
PERFECT flowers are bisexual
à Other aspects of plant “gender”
• A large and complex vocabulary has grown up around the expression and timing
of plant sexuality (gender).
• A plant can be hermaphroditic in many ways, including possessing only perfect
flowers
Gender terms to know:
MONOECIOUS (noun: monoecy) – “One house”. Hermaphroditic plants with
imperfect flowers, staminate and pistillate, on the same individual
DIOECIOUS (noun: dioecy) – “Two houses”. Each individual possesses only one
kind of imperfect flower, staminate or pistillate.
Humans and most animals are “dioecious”. Most angiosperms are not!
HERKOGAMY: “Male” and “female” sex organs are spatially separated in a bisexual
flower.
Ø Heterostylous species have a special form of this, “reciprocal herkogamy”
DICHOGAMY: “Male” and “female” organs functional at different points in time:
Ø Protandry (anthers open first)
Ø Protogyny (stigma receptive first)
• Dioecy, herkogamy & dichogamy function to prevent self-fertilization and may
promote cross-pollination
Back to basic morphology…
FUSION
CONNATE (adj.) – FUSION OF LIKE PARTS e.g. the fusion of staminal filaments
into a tube
SYNANDROUS
SYNCARPELOUS
SYNSEPALOUS
SYMPETALOUS
(SYNTEPALOUS)
ADNATE (adj.) – FUSION OF UNLIKE PARTS i.e. fusion involving parts from
different whorls. Stamens “adnate” to the corolla are EPIPETALOUS. Various
terms exist for the fusion structures (will cover later in term)
FLORAL SYMMETRY
ACTINOMORPHIC – Radially symmetrical. Multiple lines can be drawn through the
middle of the flower to yield a mirror image on either side
ZYGOMORPHIC – Bilaterally symmetrical. Only one possible line can be drawn
through the middle of the flower to produce a mirror image on either side
IRREGULAR – No axis of symmetry
STAMEN TERMS
STAMINODE – sterile organ derived from a stamen
ANTHER ARRANGEMENT –
Antepetalous: Stamens described as being “opposite” the petals, meaning each
stamen sits right over the middle of a petal.
Antesepalous: stamens “opposite” the sepals.
Diplostemonous: 2 series of stamens, the outer opposite the sepals, the inner
opposite the petals
Will talk about other types of stamen arrangement when we cover the families
ANTHER ATTACHMENT –
Basifixed – anther attached at the base
Dorsifixed – anther attached at the back
ANTHER DEHISCENCE –
Longitudinal – along axis of the anther
Transverse – at right angles to long axis of the anther
Poricidal – through a pore
Valvular – through flap-covered pores
CARPAL FUSION
APOCARPOUS – a flower with carpels forming separate pistils
SYNCARPOUS – with ovaries united to each other
OVARY POSITION
SUPERIOR – Ovary is not united to any other flower part
INFERIOR – Ovary is united with the hypanthium, appears to be sunken “below” the
other floral organs
Hypanthium – fusion product of the calyx, corolla and androecium (may also include
receptacle material). Forms a “floral cup” that may or may not be fused to the ovary
FLOWER TYPES
Three basic flower types are recognized, depending on:
(1)
(2)
Whether the ovary is superior or inferior,
If a hypanthium occurs, whether it has become evolutionarily fused to the carpal
à
HYPOGYNOUS – superior ovary, no hypanthium.
The other flower parts arise below (“hypo”) the ovary
PERIGYNOUS – superior ovary, hypanthium present and unfused
The other flower parts appear to arise around (“peri”) the ovary on the rim of a
hypanthium. Hypanthium may be tubular, bowl or saucer-shaped
EPIGYNOUS – inferior ovary. The hypanthium may not be readily recognizable
because it is fused to the ovary. The other flower parts appear to arise from or on
(“epi”) the top of the ovary
OVULE PLACENTATION
The arrangement or configuration of the placentas (the part that attaches each ovule
to the carpal wall)
Axile
Parietal
Free-central
Basal
Apical
TYPES OF BLOSSOM
Several ways of classifying pollination units (flowers or aggregated groups of flowers)
(1)
Mode of pollination
Ø BIOTIC, e.g., insect-pollinated (entomophilous),
Ø ABIOTIC: wind or water
(2)
Functional structure (see Faegri and van der Pijl 1979)
(a)
(b)
Ø
Ø
Ø
Ø
Flowers inconspicuous, no optical attraction
Flowers conspicuous
Dish/ bowl e.g., Magnolia, Caltha, Rosa. “Mess-and-spoil pollination”
Bell/ funnel e.g., Campanula
Brush
Gullet. e.g. many Lamiaceae and Scropulariaceae. Flower has upper and
lower division. Sex organs on upper side, pollen deposited on insect’s back
Ø Flag. e.g. many Fabaceae. Flower has upper and lower division. Sex organs
on lower side, pollen deposited on insect’s ventral side
Ø Tube e.g., Delphinium, Aconitum. Nectar is only accessible by insertion of
insect’s mouth parts (tube may be the entire corolla or a “spur” containing nectar
NOTE: Not all flowers fit easily into the functional system! (many orchids,
gingers)