Fig. 24.3 T&Z3

Normal Floral Organ Identity

Organs (LDOs) are always produced by the Flower Shoot Apical Meristem (Flower SAM) in the following order, from lower/outer to upper/inner:

Sepals Petals

Stamens Carpels

Names of Flower Organs

Individual Collectively, DistinctOrgan or Connate

Carpel Gynoecium (G), Ovary, Pistal

Stamen Androecium (A)

Petal Corolla (Co, C) Perianth (P)Sepal Calyx (Ca, K)

If the organs of the two whorls/spirals of the Perianth are not differentiated from each other (that is, are both showy appear similar to each other), they may be called Tepals (T) or simply P

When you cannot easily count the organs

Number of Petals usually equals number of Sepals(Sepals are usually easy to see from below the flower)

Sepals and Petals are usually Alternate/Rotationally offset(If true for part of its circumference, true for entire flower)

wt ap2 pi ag1

Fig. 2 Meyerowitz 2002

S P St C C St St C S S C C [S P P S] n

Homeotic Mutants that Transform the Identity of Adjacent Whorls

Arabidopsis

B B B A C C A C A

Wild Type A is Null B is Null C is Null

The ABC Model based only on phenotypes of single mutants

Each Function acts in two adjacent whorls

Functions include Organ Identity and, forA and C, inhibition of each others function

The ABC Model of Floral Organ Identity

Y SUP

AP3+PI AP3+PI AP3+PI AP3+PI

LUG+SEU LUG+SEU LUG+SEU LUG+SEU

AP1 SEP3 AP1 SEP3 AP1 SEP3 AP1 SEP3

AG AG AG AG

AP2+BLR AP2+BLR AP2 AP2

LFY+WUS LFY+WUS

Sepals Petals Stamens Carpels

AG AG

ABCE Model: Regulators Y (inhibits AP3+PI), BLR (activates AP2), and LFY+WUS (activates AG) are differentially expressed

C A B C A B C A B C A B

Y SUP

AP3+PI AP3+PI AP3+PI AP3+PI

LUG+SEU LUG+SEU LUG+SEU LUG+SEU

AP1 SEP3 AP1 SEP3 AP1 SEP3 AP1 SEP3

AG AG AG AG

AP2+BLR AP2+BLR AP2 AP2

LFY+WUS LFY+WUS

Carpels Stamens Stamens Carpels

AG AG

Why ap2 lacks both A Functions: Expansion of AG into Whorls 1 and 2 inhibits the Specification Function of AP1

C A B C A B C A B C A B

Tepals in Monocots

First two whorls are identical, looking like two whorls of Petals, three organs in each whorl

Expression of ABC Genes indicates that both whorls are Petals: the whorl of Sepals has been transformed into a whorl

of Petals

Imperfect Flowers: Male and Female Flowers

Studies of the development of the whorls in Male and Female flowers indicate that both male and female whorls start

development, but either the male or female whorl aborts, resulting in a unisexual (imperfect and incomplete) flower

There is an extensive taxonomy based on the types of flowers (hemaphorditic vs unisexual) on individuals and in populations

monoecious (one house): male and female flowers on same plant

dioecious (two houses): male and female flowers on different plants

Floral Symmetry

Actinomorphic: Radially Symmetric (Actually Rotationally Symmetric)Probably the Ancestral State

Zygomorphic: Bilaterally SymmetricLocal Inhibition of Organ Development and/or Differential Growth of Organs,

resulting in one or two mirror planes

If any part of the flower is even weakly zygomorphic the entire flower is considered to be zygomorphic

Irregular: No obvious Symmetry

23.11 Stern9

All Ovaries start out Superior (4th Whorl)

The first three whorls may be elevatedon an outgrowth of the receptacle on whichthey are borne/inserted

This outgrowth is called an Hypanthium

It may be entirely adnate (fused) to with the ovary, adnate to the ovary only in the ovary’s basal region, or entirely distinct (free)

Hypogynous: Apparent insertion of thefirst 3 whorls below the gynoecium

Perigynous: Apparent insertion of the first 3 whorls at level of gynoecium

Epigynous: Apparent insertion of the first 3 whorls above the gynoecium

Hypanthium

Receptacle

MS Simpson (and many taxonomists?): An hypanthium is not an hypanthium if it is adnate (fused) to the ovary. It is an hypanthium only if it is distinct (free of the ovary).

Have not discovered how they think the corolla and androecium crawled up the sides of the ovary.

Agree Agree Duh?

A More Narrow Definition of an Hypanthium

RAB Glossary: A Broad Definition of an Hypanthium

Hypanthium: May be adnate to ovary (epigyny) or free from ovary (perigyny).

Superior ovary: Hypanthium adnate to ovary for less than ¼ the length of the ovary.

Inferior ovary: Hypanthium adnate to the ovary for ¾ or more of its length.

Sensible, and the Keys and Descriptions of Rosaceae use these definitions. But at least one lead to some taxa of Rosaceae does not.

Partial to complete Connation/Fusion of Carpels

Minimum Number of carpels can be inferred from whichever is the larger number: number of locules, number of lobes, number of

(paired) rows of ovules, number of styles, or number of stigmas.

Warning: In some taxa, a carpel develops a false septum, resulting in two pseudo-locules

Fuse Carpels before Closing Them

Close Carpels before Fusing Them

septate

axial parietal

marginal axial parietal free central apical

marginal axial parietal free central

basal

Walters and Keil

Ovaries from Fused Carpels

nonseptate

3 Carpellate3 Loculate3 Septa

3 Carpellate1 Loculate0 Septa