Lost in the woods: Emma Townshend ventures deep into the forest to unearth a secret world of rare and fascinating fungi

Oh,' says Justin Ruddle, the National Trust warden of Slindon Woods, plaintively. 'You've got the new Roger Phillips.' Not only is Ruddle a dab hand at naming fungi, picking them out with enviable ease as we meander through the beech woodland, he also has a keen eye for a freshly published mushroom-identification book. He has spotted the shiny new volume under my arm at 40 paces.

We are in West Sussex, where the Downs roll towards the sea and chalkland is the order of the day. Here, in this little corner of the county, hemmed in by two huge dual carriageways, Ruddle oversees 3,500 acres of National Trust land, including a whole lot of trees and millions of mushrooms.

Today, he has organised a fungi hunt, which has attracted 45 happy members of the public to assemble in the winter sunshine, clad in various states of inappropriate dress. We range in age from an energetic little girl called Ella, who runs from one end of the wood to the other, telling us what's been found up ahead, to slightly less nimble people who are using their walking sticks to point out their discoveries. The National Trust runs a surprising range of off-season activities to keep people visiting its properties throughout the cold months, and I found this walk on its website. Quite a few of our group are local, yet are seeing their woodland this way for the first time.

What starts as a whimsical weekend becomes a real experience in conversion. As we walk and talk, Ruddle's enthusiasm spreads to me and all my fellow fungi-hunters. Far from being a prelude to culinary activity, on this walk, he encourages us to 'look and leave', while telling us about the forest ecosystem, as well as stuffing our heads with remarkable facts about pavement mushrooms splitting Tarmac as they come up, and the fungi that can only grow on London Underground seat cushions. And, of course, there are all those evocative names: the Rosy Sickener, the Common Earthball, the Amethyst Deceiver, King Alfred's Cakes (convincingly burnt-looking), and Fairy Inkcaps. We even see some Dead Man's Fingers.

Studying the identification book, though, I am rather relieved that we're not collecting to eat. The description 'usually free of maggots' has to give you pause for thought as a description of a foodstuff. Set free of worrying about imminent poisoning, the group becomes more and more lively, wandering from tree to tree, chatting, picking and looking things up, with Ruddle always on hand to add a name or a curious footnote. For a finale, we end up in a group peering at the spectacular hallucinogenic toadstool, the Fly Agaric, looking just right as a perch for a little wood-dwelling gnome.

But Ruddle's primary goal is to get us to see this woodland as a system. Just as orchids can't grow without their own particular friendly fungi, trees seem to do better with the local mushrooms living among their roots, exchanging nutrients for tree sugars. He explains: 'In the storm of 1987, we lost so many beeches that the village was cut off for three or four days. But when we replanted with outside trees, we found that they don't do as well as ones native to this spot, that have grown here from the start, right from seed.'

These mutually beneficial associations of tree and fungi are called 'mycorrhizae', and the invisible underground trading floor is increasingly seen as crucial to the survival of many tree species, particularly as climate change puts greater pressure on them. 'Our understanding of what fungi do is changing all the time,' says Ruddle, who is trying to use his expertise to look after the woodland as a whole. Some more hostile fungi, for example Ustulina, rot a tree at the base, creating a risk that it may suddenly break at the bottom. Some eat out the heartwood. And some appear to be able to change the biochemistry of a part of a tree they 'capture', making the tree's cells work slightly differently, for their own benefit. In general, though, most fungi are doing much more good for their trees than I had ever realised. We all wander back to the cars, slightly stunned that there could be so much to learn about trees and toadstools.

This week is National Tree Week, to celebrate the start of the planting season, and Justin Ruddle's fungi facts strengthen my determination to grow a native hedge from scratch, using some of the stand-out berries that have been growing this year. I stop on the way home to pick fruits, seeds and acorns from the verges.

Whatever the gardening implications of fungi, it is addictive to hunt these tiny, delicate, beautiful structures, that seem invisible at first, camouflaged in subtle shades of leaf tones, but which slowly reveal themselves to be almost everywhere. So Roger Phillips' book gets to go on another outing before the weekend is finished. After Sunday lunch at my mum's, we end up in the local shooting copse, trying to identify the mushrooms that are growing among the spent gun cartridges. What bliss when one of them turns out to be: 'Occasional. Often seen growing on pheasant feed.' s The National Trust's winter events calendar can be found at www.nationaltrust.org.uk; National Tree Week runs until 3 December and you can get more information at www.treecouncil.org.uk; Roger Phillips' latest book, 'Mushrooms', is available now, published by Macmillan and priced £18.99

Q&A

Emma answers your horticultural queries

I have been thoroughly enjoying my 'Verbena bonariensis' all summer, but now it is started to look a little bit ratty. What can I do to make sure I get the same display again next year? Do I need to buy the plants all over again? Sorry, I'm not really a very expert gardener at all, and they are the first thing that has grown really nicely for me.

Fiona McLean

The verbenas are South American plants, and some of the smaller ones are best treated as annuals. But Verbena bonariensis (below) probably has some more life in it. If you are a complete beginner, remember that plants will benefit if you cut off the stalk that had the flowers on it. This will make the plant focus on its roots and leaves, rather than on making seeds.

However, this Verbena will seed itself nicely, so if you think you will be able to tell the seedlings apart from weeds, you could always try that approach to increasing its numbers. But the best thing for you to do is probably to cut it back, put some nice compost around it, and - with a bit of luck - next year it will do well for you again.

I'm thinking of ordering one of those mushroom logs for my uncle for

Christmas. But do they actually work?

Jennifer Wallechinsky

Hmm, an interesting but also very timely question considering the topic of this week's main piece. I have had very mixed reports about these logs that you buy pre-treated with mushroom spores, which supposedly just need to be left outside to provide you with a great crop. Several uncles of my own acquaintance have commented that they didn't really work at all. However, Victoria at the Gingko Garden Centre in Ravenscourt Park, London W6 (tel: 020 8563 7112) told me that mushroom spores in packets are the way to go. But they do require regular care - you can't just leave them to it. You buy named types like Oyster and Shiitake, in impregnated plugs which you then put into logs yourself. Unfortunately, it's not quite such a spectacular present though.