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
today.

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
Pelargonium.

The pictures are at

http://pacificbulbsociety.org/pbswiki/index.php/…

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