The Miracle of Seed Dispersal

Thursday 14th September brought a sunny but cold day tempting eight botanists to meet at Low Barns Nature Reserve. The aim of the morning was to study seeds and their dispersal. Before starting we had a discussion as to what fruit and seeds were and the different methods of dispersal. We even talked about the dispersal of coconut seeds although we knew we weren’t likely to see a coconut palm as we went round.

 

We hardly had to step outside the car park before we found interesting plants and their seeds. We had fun throwing the seed cases of Arctium minus (lesser burdock) and watching how they stuck to our clothes regardless of what materials our coats were made of. We then looked at the seeds. The outside of the seed case consists of spines which under a lens look like tiny walking sticks, a bit like the ones Charlie Chaplin used in his act.

 

The next plant was the Geum rivale (wood avens). This plant too, uses the same type of seed case with hooks especially for animal dispersal. Also Fagus sylvatica (beech) whose masts or seed cases are similar with a deeply lobed woody cup that encloses the beech nut. A straggly piece of Glaium aparine (goosegrass or cleavers) was our next find. Those new to botany wondered how we could recognise the plant because it has lost all its colour. It still had most of its identifying features including its sprawling appearance, four angled and very rough stems. The few ripe seeds remaining had hooked bristles with swollen bases that are well known for catching on clothing. All the above were perfect illustrations of plants that disperse seeds using animals, the seeds catching on their coats as they pass by.

geum urbanum

Walking on a few paces we tried identifying a member of the Rumex (Dock) family. This is not an easy group and seeds are an important feature of identification. Steve, who was leading the group at this point delved into a heavy bag he was carrying which contained some lovely books. Between us we keyed the plant out to establish it was a Rumex obtusifolius (broad-leaved dock). An interesting feature was the triangular inner tepals some of which had a large wart on them. The purpose of the wart is somewhat unclear but maybe a food source for the seeds. Later in the event we keyed out another plant of the same family Rumex sanguineus (wood dock). The tepals in this case being oblong untoothed, blunt but again with some wart features.

rumex obtusifolius

A plant which the group found particularly fascinating was one which is native to Britain but is often removed by the Durham Wildlife Trust volunteers because it is so invasive. Having examined the seeds we know why now, they are beautiful but there are so many. Chamerion angustifolium (rosebay willowherb) seed pods open from the top rather like peeling a banana in a four way split to reveal many fine feathery hairs (pappus) attached to the seed that float and blow away in the wind. There can be as many as 80,000 seeds in one plant. Another name for rosebay willowherb is Fireweed. There are several reasons for this name including the fact it is one of the first plants to colonise a site that has been burnt.

chamerion angustifolium

At this point it was guess the seed time. Steve produced a book, ‘The Cambridge illustrated glossary of botanical terms’ and we all played guess the plant from the picture of the seed relating in particular to the Carrot family (Umbelliferae), now known as Apiaceae. This included seeds and seed cases from Aegopodium podagraria (ground- elder) the leaves of which you can eat as long as they are young, Angelica sylvestris (wild angelica) and Heracleum sphondylium (hogweed).

heraculeum sphondylium

Fruits on the trees did not escape our attention including looking at Crataegus monogyna (common hawthorn). As its name implies, mono, the fruit or berry consists of a single seed in a fleshy cover. We looked at Sorbus aucuparia (rowan) which contains one or two seeds in a fleshy case and another tree that encouraged a good deal of debate. We eventually came to the conclusion it was a Sorbus torminalis (wild service tree). Someone asked if the seeds were edible. The answer is “Yes” but the fruit should be bletted first which means they must be extremely ripe. Unripe seeds can contain hydrogen cyanide making the fruit bitter. Medlars are treated the same way. Of course like anything you eat in the wild you should always take extreme care and only eat anything that you are absolutely sure about. Stick with blackberries and raspberries and you won’t go far wrong!

 

Moving on we reached a small meadow where the grass had been cut ready for hay making. We rooted around finding some amazing seeds. One that particularly caught our interest were the seeds of Filipendula ulmaria (meadowsweet) which are twisted together to form an amazing shape a little like some wasps’ nests. A little pressure they split into individual seeds. Our final plant was an orchid. We were each given a seed case for most of us to immediately comment that the plant had shed it seeds. Closer examination and running a finger along the case or a slight tap dust emerged or some of the fine seeds. Orchid seeds are minute and blow away in the wind for long distances. The seeds are so tiny they have no food source and rely on a symbiotic fungus to germinate and grow.

 

For those of you who could not make this botany event you missed a real treat. I think the whole group were amazed when they examined closely the shapes of the various seeds and how individual plants adapt to make sure the species continues. Some of the group were also artists and collections of seeds were made as we strolled round so they could be drawn, painted, embroidered or simply studied further. Perhaps one day we can see the finish results of these activities. Finally we are went back to enjoy a tea or coffee because we were all feeling the cold by then. Soon afterwards it rained heavily for a short while, luckily we escaped it already sitting in the warm.

 

Thank you Steve for arranging the event, it was excellent.

 

Carole Lloyd is an active member of Durham Wildlife Trust botany group, set up to enjoy and learn more about the wonderful range of plants in our area. If you would like to attend events, have a look at the events page, email botany@durhamwt.co.uk or telephone 0191 5843112.