Monotypic families

10:46am Friday 13th October 2006

Last month I wrote about one of the largest of the plant families, the Rosaceae, which contains several hundred members or genera.

Most plant families are a little more modest, like Fagaceae, the beech family, which has eight members, including beech, oak and hornbeam, and Berberidaceae, which has 18 genera, including Berberis, Epimedium, Mahonia and Nandina.

There are some families, however, that have just one member - I think they are known to botanists as monotypic families'. I find these families quite fascinating; the plants within them must be so unlike any other type of plant that even the most assiduous botanist can find no links between them and those in other families.

Gunnera is one of these genera in a family all of its own. No surprise there, I hear you say, although some people have likened their huge leaves to those of rhubarb (which is in the Polygonaceae along with bistort and Russian vine). If you look at the flower spikes of any Gunnera, from the huge Gunnera manicata to the tiny G. magellanica, you will see that they consist of dense, upright spikes of tiny, greenish yellow flowers. The basal flowers are usually female, the uppermost male, while those in the middle are sometimes bisexual. It is this unusual arrangement of flowers that unites all species of Gunnera into their own family and separates them from the rest of the plant world.

Garryaceae is another plant family with only one genus - yes, you've guessed it, Garrya. There are 13 different species of Garrya, including the familiar G. elliptica; once again it's their flower structure that sets them apart. Garrya flowers are petal-less catkins, with male and female catkins found on separate plants. Male catkins are generally more attractive than the females, so it's usually male plants that are sold in nurseries and garden centres.

Although we can't grow lotus flowers outside in this country, many of us have seen them in hot-houses, growing alongside Victoria amazonica water lilies, or while on holiday in warmer climes. Their distinctive, flat topped seed pods turn up in dried flower arrangements from time to time.

The family Nelumbonaceae contains just two species, Nelumbo nucifera, the sacred lotus, and Nelumbo lutea, the American lotus.

While researching this article I came across several monotypic families that I had never heard of, the few well-known monotypic families that I have mentioned above, and one complete surprise. Whoever would have guessed that the humble peony would have its own special family!

The family Paeoniaceae contains just one genus, Paeonia, the common-or-garden peony - all the more surprising when you consider that there are around 30 different species and dozens of cultivated varieties. Common as they are, they have nothing in common with the rest of the plant kingdom...I shall appreciate them all the more for their uniqueness.

• Jobs for this week:

Begin the annual, thankless task of raking fallen leaves from lawns and paths. Check gutters and drains are not blocked to avoid unexpected floods.

Dry and sunny autumn days may be the last chance we have this year to give wooden garden furniture a protective coat of woodstain before the winter arrives.

Plant hyacinth and miniature daffodil bulbs in bowls or pots indoors, for flowering at Christmas and New Year.

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