These wild flowers were photographed in early July  at the northern end of The Chilterns on a short walk to Ivinghoe Beacon – Pyramidal Orchid, Common Spotted orchid, Greater Knapweed, Self Heal, Agrimony, Goatsbeard, Mignonette, Dropwort and Clustered Bellflower. Ivinghoe Beacon is located on The Ridgeway which is an ancient track that runs through the Chilterns, an Area of Outstanding Natural Beauty AONB. The chalk grasslands along this route provide a wonderful habitat for wild flowers which are abundant in July. The flowers shown here are not rare but easy to see and photograph. 

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Two Orchids in flower in June :- The Greater Butterfly Orchid Platanthera chlorantha is found throughout Britain on grassy slopes and woods. It is fragrant at night and pollinated by night-flying moths. The Fragrant Orchid Gymnadenia conopsea is pollinated by butterflies and moths, attracted by its strong scent. It is found throughout Britain on grassland, especially on chalk or limestone and across northern Europe and western Asia. 

Hazel Catkins

The Common Hazel is a wind pollinated, monoecious tree.  A perfect flower, like those found on Cherry trees, has male and female parts combined but this can lead to self pollination so  some trees separate the male and female flower parts. If the separated parts are on the same tree it is known as monoecious (Greek for one household). Alder, Oak, Beech, Birch, Hornbeam and Sweet Chestnut are other examples of monoecious trees. 

Hazel catkins – the hazel is a monoecious tree with male flowers on hanging catkins and tiny female bud-like flowers with red stigmas. To see catkins on the closely-related Turkish Hazel click HERE

Autumn Leaf Colours

Autumn leaf colours can be used to identify trees in Britain – some trees have leaves that turn yellow, others red and some stay green until they fall.The most striking thing about deciduous trees in autumn is not that they shed their leaves, it’s the fact that the leaves on some trees change their colour before they fall. Why does this happen – the leaves have been green all spring and summer? Why don’t the green leaves just drop off without changing colour and why on some trees do the leaves turn yellow and on others red. In fact most trees in Britain, for example Common Alder and Common Ash, shed green or brown leaves but about a third of all species turn either yellow or red. 

In Britain our landscape consists of trees that originated in Europe, America, Asia and Australia. Most trees of European origin turn yellow with hardly any turning red. European tree species that turn yellow include the Norway Maple, Field Maple, Aspen, Silver Birch, Common Beech (yellow then brown), Common Hornbeam, Willows, Poplars and Limes. In some years Wild Cherry leaves turn yellow or red in autumn. The Ginkgo  introduced from China, has yellow autumn leaves. In America there are some native trees  such as the Quaking Aspen, Tulip Tree, some Oaks, some Maples and some Hickories that are yellow in autumn but many more that turn red.  Here are 8 examples of trees that turn yellow.

Not all conifers are evergreens. Some are deciduous and shed their leaves in autumn. Examples are the Swamp Cypress and the Dawn Redwood. For information on these trees click HERE

Nearly all the trees that turn red in autumn in Britain  were introduced from North America or Asia. Examples are the Red Maple, Sugar Maple, Red Oak, Scarlet Oak, Pin Oak and Sweet Gum from North America and  Japanese Maple varieties such as ‘Ozakasuki’, Sargent’s Cherry, Paper-bark Maple, Persian Ironwood, Snowy Mespil and Pillar Apple from Asia. A few European trees, such as the Wild Service Tree and the Bird Cherry turn orange/red and some, such as the Norway Maple and the Common Rowan, may turn orange/red under stressed conditions. Some varieties of European trees with red autumn leaves include the Sycamore ‘brilliantissimum’ and the Claret Ash ‘Raywood’. Here are 9 examples of trees that turn red in autumn.

Two main theories

A leaf is the main photosynthetic organ of a tree. This is a process in which carbon dioxide from the air is combined with water in the presence of light to produce sugars and oxygen. The molecule that carries this out is called chlorophyll. It absorbs red and blue wavelengths of light and reflects green so that the leaf appears green to us. It is a complex molecule with a ring of nitrogen at its centre surrounding an atom of magnesium. Shorter days and lower temperatures trigger leaf fall but this is a multi-step controlled shutdown process. Some trees just discard green leaves but in other trees  the chlorophyll and proteins in the leaf are broken down and essential nutrients, such as nitrogen, are re-adsorbed and stored in the shoots and roots until spring. 

As the chlorophyll breaks down, the leaf loses its green colour and other pigments can be seen. Carotenoids are yellow and orange and are already present. Anthocyanins, which give the leaf a red colour, are newly made. Carotenoids are needed to keep the cells going during the re-absorption stage so most trees that change colour have yellow leaves in autumn but 14% have red leaves. Why, then do some trees go to the expense of making Anthocyanins before the leaves fall? There are two main theories.

Photoprotection hypothesis

Anthocyanins protect the leaf from light damage during the period of re-absorption. This is the basis for the photoprotection hypothesis – it extends the leaf life during shut-down and enables it to send more nutrients back to the tree before the leaf drops. If this is true, trees with yellow leaves should drop their leaves earlier.

Co-evolution hypothesis

Alternatively the red coloration may be a signal to parasites, such as aphids, that have a strong preference for green leaves, to not lay their eggs on red leaves in autumn. This avoids future damage and is the basis for the co-evolution hypothesis. Red colour may be correlated with the level of herbivore defence in the tree, and therefore plants investing more in defences show more autumn colours. If insects adapt to avoid red leaves in autumn, this will lead to a co-evolutionary process in which both preference for green in aphids and intensity (or duration) of red in trees increase.