GeraniumsOnline   

                                               

 

Pelargonium Profile – Botany 101 – Flowers   

By Wayne Handlos, Ph.D.                                                                                                        Diagram ( cross section) of a Pelargonium flower >

The typical flower in seed plants (angiosperms) consists of four groups of parts.  These are (1) the SEPALS, the green, outer covering of the flower and collectively called the calyx; (2) the PETALS, usually showy, colored parts collectively called the corolla;

 (3) the STAMENS consisting of a stalk or filament and the anther in which the pollen grains are produced;                                                                                                                                    

< a Pistil

and  (4) the PISTIL or seed bearing organ.The pistil  is composed of  a stigma  (a) (the structure on top of the style which receives and holds the pollen after pollination), a style (b) and a basal ovary (c)  

In the geranium family (Geraniaceae), the flower parts are usually produced in groups of five. There are five sepals, five petals, five or 10 stamens, five compartments in the ovary and five stigma branches. When the ovary matures, it splits into five sections or mericarps, each containing one seed. The mericarp is plumed and this aids in seed dispersal.

The number of flower parts may vary in individual species; and when plant breeders and gardeners are involved, aberrant types with extra petals are selected as desirable. Therefore in zonals and ivies, plants bearing double and semi-double flowers, i.e. with more than five petals, are common. In the regal and angel geraniums only one or two extra petals may be found but truly double flowers are uncommon. However, there is one novelty cultivar (probably a form of P. cucullatum) called ‘Spanish Lavender’ in which I have counted over 40 petals in one flower!

Within the geranium family there are five genera: Pelargonium, Erodium, Geranium, Monsonia and Sarcocaulon. A few floral characters are used to separate these groups. Erodium has five fertile stamens, Geranium has 10 fertile stamens, Monsonia has 15 stamens and is herbaceous (not woody), Sarcocaulon also has 15 stamens but has a spiny, succulent stem; Pelargonium, unlike the previous four, has irregular or zygomorphic flowers. In this group this means that two of the petals are different in size, shape and/or patterning from the other three. The two halves of a flower are mirror images of each other. The number of fertile stamens is fewer than 10 – commonly seven or five (but other numbers ranging from two to six may be found in certain species. (So much for our basic rules!)                  June 2008


                                          

        Pelargonium                      Erodium                       Geranium                     Monsonia*                     Sarcocaulon**

                                     A dicotomous key to the genera in Geraniaceae

1.  Flowers irregular  (the upper two petals different in shape and/or size from the lower three) ;

     hypanthium present, (fertile stamens fewer than 10) ......................................................................  Pelargonium

1.  Flowers regular (all petals more of less the same in shape and size);  no hypanthium .............     2

 

2.  Stamens 10 or fewer   .......................................................................................................................     3

2.  Stamens more than 10 .....................................................................................................................      4

 

3.  Fertile stamens  5        .....................................................................................................................     Erodium

3.  Fertile stamens 10      .....................................................................................................................     Geranium

 

4.  Stamens 15:  plant herbaceous; stems not spiny    ......................................................................    Monsonia   

4. Stamens  15:  plant succulent; stems spiny,    ................................................................................   Sarcocaulon 

                                                                       * Monsonia image from www.metafro.be       ** Sarcocaulon image from www.aztekium.narod.ru


                                                                                                                                                                                                             

© 2010, Central Coast Geranium Society (CCGS )