Cliff hanger: Off on her annual sailing holiday, Anna Pavord couldn't resist dropping anchor in Corsica, where the plant-rich coastline had one or two surprises in store

Our summer holiday is usually spent sailing, but fortunately, the friends we sail with are as keen on walking as they are on navigating the waves. This time we picked up the boat, a Bavaria 42, in the Maddalenas, a scattered group of wild islands that lie off the northern tip of Sardinia. The forecast was for a good steady blow from the east, so we couldn't resist the chance to zip up once again to the stupendous red cliffs of Corsica's west coast.

This was the fourth time we have headed to these waters. Corsica's rocky coasts provide some surprising anchorages, if the wind is kind, and whenever possible, we drop anchor overnight in some quiet bay. Cala di Tuara in the Golfe di Girolata (though Corsica is French, many place names are confusingly Italian) was a new discovery: no houses, no lights, no road, though we could see one of the island's long-distance footpaths dipping down to the shore and then climbing steeply on to the north.

So we had the place pretty much to ourselves and in the late afternoon rowed ashore to explore the dried-up riverbed that disgorged on to the steeply shelving beach. Corsica is a good place for plants; nowhere else I've wandered gives such clear lessons on habitat. One particular set of plants (sweet chestnut, cyclamen, Helleborus corsicus) lives high up in the cooler air of the mountains. Another set (arbutus, myrtle, sea buckthorn) is what you'll find in the hot, dry maquis. On the shore are the dead, matted rhizomes of Posidonia oceanica, a strappy monocotyledon that grows in great meadows on the seabed. Bulbs on the shoreline are most likely to be sea squills or sea daffodils. Bulbs growing in poor pasture will probably be asphodels.

But the first plant we saw on the stony, dried-up riverbed was something I'd never encountered before: a shrubby kind of perennial, four to five feet high, thin leaves, small clusters of creamy flowers (not very conspicuous) towards the top of the stems. Its most outstanding characteristic was its seedpods, extraordinary comma-shaped capsules, up to two inches long, green and covered with soft bristles. When they dried, they split to shed a mass of soft thistledown.

So where do you start when you want to identify a stranger such as this? I've got three flower books that cover the area: Flowers of the Mediterranean by Oleg Polunin and Anthony Huxley (Chatto & Windus paperback £7.95), Mediterranean Wild Flowers by Marjorie Blamey and Christopher Grey-Wilson (Harper Collins £30) and Wild Flowers of the Mediterranean by David Burnie (Dorling Kindersley £14.99). Constraints of space on board mean that I usually take only two of the three.

Trained botanists may well start their search with the identification key: flowers spurred or not spurred, flowers in umbels or distinct heads, petals free or fused, leaves heart-shaped or linear, ovary below tepals or underground. But this is too daunting a task for most of us, who take a lifetime even to understand that wildflower books are not laid out alphabetically but according to the age of the family in question. So my Mediterranean flower books start with pines, which, according to the fossil records, are the oldest group of plants in the region, and finish with families such as the thrifts, olives, gentians and bedstraws, which, in geological time, evolved much more recently.

But I'm not a trained botanist and my way in is much more random. Sometimes the general habit and style of a plant will suggest a family - spurges perhaps or geraniums. The plant in front of me on the riverbed didn't do that. By far its most arresting and decorative feature was its extraordinary seedpod, and I wondered whether this might have led to a common name that highlighted this feature. So when I got back to the boat, I flicked through the various bladder plants listed in the indexes: bladder campion, bladder senna, bladder vetch, but it certainly wasn't any of those.

After that, I had to depend on good pictures and in this respect David Burnie is by far the most helpful. His book uses photographs, not drawings, and the illustrations are always alongside the text, not clumped in separate sections. Flicking laboriously through the first 176 pages, I found my plant, the bristly-fruited silkweed, Gomphocarpus fruticosus, because it was so well illustrated, with details of leaf, flower and seed capsule pictured alongside a stem of the plant itself.

But if I'd pursued my first approach a little further, I might indeed have been able to track this plant down by its common name. When I picked a sprig to take back to the boat, the stem produced a milky sap, like a spurge. The plant is in fact one of the milkweed family and milkweed in the index would have led me straight to it. It turns out it's not actually a native at all, but was introduced into the Mediterranean as an ornamental plant from South Africa. It was particularly pleasing to read - the final positive identifier - that its preferred habitat is rocky watercourses.

From Calvi we made a favourite trip up to Corte, a university town in the wild, craggy centre of the island, to walk part of the Mare a Mare path through the mountains. At first this is maquis territory, drifting into chestnut where watercourses provide sufficient water for the trees to drink. The best way to get to Corte is on the train that hauls itself from east coast to west on a track that defies all laws of gravity. But the train people were en grÿve and the buses that got us to Corte then decided to join them. So we got back to our boat thanks to a magnificent taxi driver determined to prevent anyone from overtaking her - ever.

In high-speed French, with much waving of hands, sometimes both at the same time, she gave us the local news. There had been a big flood at Bastia. Her Mercedes was washed away. Pouf! A landslide had crushed a lorry, just here, on the road. Pouf! A new hotel had been built in the town we were passing through. An outsider. Said he didn't think much of the Corsicans. The next day, Pouf! No more hotel. So, just to get this absolutely clear, I LOVE CORSICA.