TOW: Tuberous Pelargonium

David Victor
Mon, 23 Aug 2004 10:54:12 PDT
Dear all,

All of you will no doubt know a Pelargonium when you see one.  Indeed, many 
of you will be the proud owners of one or more of these attractive 
plants.  However, some of you will not immediately recognise the name 
Pelargonium, as they are frequently known as Geraniums.  Sadly, this is due 
to a series of arguments between taxonomists in the 18th century  See 
footnote.  However, to make matters clear, I am here talking about the 
tender plants that are frequently used in window boxes and patio planting, 
not the hardy plants that you can leave in the garden all year round, which 
are the true Geraniums.

Before getting into the meat of this note, firstly a little 
background.  The name Pelargonium refers to the shape of it's fruit and is 
derived from the Greek for "stork's bill":  Pelargoniums are members of the 
family Geraniaceae, other members being Geranium (Greek for "crane's 
bill"), Erodium (Greek for "heron's bill"), Monsonia and Sarcocaulon (the 
latter two now sometimes being clumped together).

Whilst there are a number of ways to separate Pelargonium from other genera 
in the family, the most obvious one is by the shape of the flowers.  In 
Pelargonium, the flowers are irregular, with two petals at the top and 
three at the bottom, whereas with the others the petals are spread evenly 
around the flowers.

Pelargoniums come mainly from South Africa, although there are a few in 
Australia, East Africa, the Middle East and some islands, such as St. 
Helena and Madagascar.  There are thought to be of the order of 250 species 

The Pelargoniums normally found in cultivation are fibrous rooted, so it 
might surprise you to see the title "Tuberous Pelargoniums".  However, 
there are many examples of tuberous species in the genus: Indeed, there are 
almost as many tuberous species as fibrous ones.

The genus overall may be divided into a number of Sections and today 
normally 14 are recognised:  Two of these are under re-consideration but 
this does not need to worry us today.  Whilst tubers appear in seven of 
those Sections, they are dominant in two, Sections Polyactium and Hoarea.

Section Polyactium - There are a dozen or so species in the Section, which 
only contains plants that have tubers or thickened rootstocks that store 
water and food, to help survival during periods of high temperatures and 
low rainfall.  Plants of this Section are found across South Africa in 
various climatic areas.  Some have strange, extremely divided foliage, some 
have yellow and black/purple flowers that are scented at night for moth 
pollination and some have the most extraordinary fringed petals.  To me, 
the most extraordinary of all of this group is P. bowkeri, which shows most 
of these characteristics.  Take a couple of minutes out to review the 
photos of this plant on the WIKI.  There you will find three photos which 
will illustrate my points (apart from the beautiful night-time scent, I'm 
afraid!).  It's also worth looking at some of the others of the Section, 
such as P. schizopetalum and P. lobatum, whilst  you are there.  When 
looking at these pictures, it's worth asking yourself if you would 
recognise the genus of the plant if you saw it without knowing it was a 

The pictures are at…

Section Hoarea  However, whilst Section Polyactium is fascinating, it is in 
Section Hoarea that we find the most beautiful examples of tuberous plants 
and many, many of them.  It is the largest Section of Pelargonium, there 
being something over 70 species.  And, they are all tuberous!  However, 
that's all for part 2 which will be published tomorrow.

I trust that you will find this wonderful genus as fascinating as I do.

Footnote - Originally, pelargoniums, geraniums and even other relations, 
such as erodiums, were all part of the genus Geranium.  Johannes Burman, 
Professor of Botany at Amsterdam, coined the name Pelargonium to describe 
this particular part of the family when separating it in 1738.  However, 
Linnaeus, in publishing his Species Plantarum soon afterwards (establishing 
the principles of binomial naming) did not recognise this separation and it 
did not catch on for another forty years and, in many ways, has never 
caught on at all!

Best regards,
David Victor 

More information about the pbs mailing list