Course Title: Principles of Flowering Plants Taxonomy(Theory)
Course No: BOT 222
Representative flowers of two important families Gramineae and
Compositae
Gramineae Flowers


The part of the grass plant popularly known as the flower, is actually composed of many
small flowers hidden, except at flowering time, within scales or bracts.
The structures containing the flowers are called SPIKELETS.
Structure of Flower

The flower is usually bisexual.


It consists of an ovary containing 1 ovule (the female part).
The ovary is usually surmounted by two feathery stigmas and is surrounded by three
stamens.
Each stamen (the male part of the flower) consists of an anther and a filament.

Anther




There are no petals or sepals.
Instead, the flower is protected by two sets of scales.
The first set consists of the LEMMA and the PALEA which enclose the flower.
This whole structure is called a floret.

One or more florets may be arranged on an axis (the RACHILLA), with all of the florets
being protected by a second set of scales at the base called GLUMES.


The glumes enclose the florets before they are mature.
The whole unit is called a SPIKELET.



The Lemmas (of individual florets) and/or the Glumes, may have bristle-like extensions
called AWNS arising from them
A spikelet made up of 2 florets
The spikelets are arranged into a flowering head (inflorescence) in a number of different
ways depending on species.
Compositae Family


Composites have packed a number of tiny flowers on their ends next to one another, on a
platform called a receptacle
Finally to organize many flowers which look like just one flower. In other words the
sunflower is actually a collection of hundreds of flowers



Moreover, in that sunflower you are seeing two kinds of flower.
The two composite-flower types are usually known as disk flowers and ray flowers, and
the differences between these two flower types is shown in the above diagram.
In the picture of the sunflower the "flower's" broad central area is composed of hundreds
of disk flowers, and the yellow "petals" are the ray flowers.


Composite flower heads bear scale-like bracts, which are usually green and overlapping,
like the ones below .
The collection of all the bracts considered together is called the involucre.
Bracts
ANALYZING DISK & RAY FLOWER STRUCTURE
Here are a couple of composite-family characters to keep in mind:

STAMENS: Stamens in disk and ray flowers number four or five, and are fused together
by their anthers to form a cylinder around the style.

PISTILS: In each flower type a thread-like style passes up through the anther-cylinder to
two long stigma lobes projecting above
. The ovary is situated below the point of attachment for sepals and petals.
Technically such an ovary is referred to as being inferior.


Pistils develop into fruits.
The Composite Family's inferior ovary transforms into a unique kind of fruit called an achene.
PAPPUSES




Atop the achenes of many members of the Composite Family sepals have become
reduced to special projections known collectively as the pappus.
Atop the achene, the slender, radiating items are the pappus.
Later the pappuses on these mature achenes will serve as parachutes, enabling the
achenes to be blown by the wind into new territory.
Pappuses come in an amazing variety of forms, not just the hairlike bristles
.
Disk flower
Pappus
Achene
BRACTS ON THE RECEPTACLE

Many composite flowers have no bracts at all, and the vast majority of the ones
who do possess bracts have bracts that are much smaller and paler.

The bract is rather scoop-shaped, with the disk flower more or less fitting into its
concavity.