Stinging nettles grow in a wide range of natural habitats, river banks, swamps, meadows, wastelands, floodplains, disturbed areas and gardens. They are are particularly effective colonisers of disturbed, bare or ‘waste’ ground. They flourish in nitrogen-rich soils.  Their seeds can lie dormant in the soil for some five years (and can even survive soaking in salty water), plus they spread using their underground rhizomes. Nettles may not be the most friendly plants to us, as their leaves and stems are ‘armed’ with special ‘hairs’. The hair-like structures are termed trichomes and each trichome has a hollow tube-like structure. At the bottom of the tube is a swollen base, which is filled with a number of chemicals, (including histamine, serotonin, formic acid and acetylcholine). The tip of the tube is easily broken, leaving a sharp point that can penetrate the skin and deliver the ‘biochemical cocktail’. [caption id="attachment_7154" align="aligncenter" width="600"] Trichomes - loaded with their chemical 'cocktail'[/caption] [NB: there is a video on YouTube that shows this mechanism here.] This collection of chemicals gives the characteristic rash/inflammation of a nettle sting.  Nettles may be found near to dock leaves which, if crushed and rubbed where you have been stung by the nettle, may take away some of the pain. More detailed information on the chemistry of the 'chemicals' in the nettles can be found here.  The hairs / trichomes probably evolved as a defence mechanism to limit grazing by sheep, deer or rabbits. Despite their ‘weaponised hairs’, nettles are in fact very good for wildlife, particularly in urban / sub-urban areas.   This is also true in areas under intensive farming practices.  The spread of farming, urban sprawl, habitat fragmentation and pollution have all contributed to the loss of natural habitats (for plants and animals), and that’s without mentioning climate change. Stinging nettles are the food plant for the caterpillars of comma, painted lady, peacock, red admiral and small tortoiseshell butterflies. The presence of nettles in our gardens and urban areas has allowed these butterflies in. And it’s not just butterflies that rely on nettles. For example,  ladybirds often lay eggs on nettle leaves. This insect might be termed a “gardener’s friend” as it has a voracious appetite for aphids - greenflies and blackflies that suck the sap from plants, ravage the vegetables in our gardens / allotments, Some aphids spread plant viruses, for example, virus yellows on sugar beet. Having nettles in our gardens and near farms give ladybirds and other insects somewhere to shelter, ready to feast when the aphid population rises. Aphid populations can rise very quickly as females give birth to live young, without fertilisation. Nettles can be used to make tea, soup, flavour beer, wrap cheese (Cornish yarg) or make cloth.  Using nettle fibres to make fabric / clothing is a very old practice, dating back to the Bronze Age.  Nettles can also be used to dye fabric [caption id="attachment_34107" align="aligncenter" width="650"] stinging nettle[/caption]

Wetlands. In the past, many areas of wetlands have been drained and ‘dried out’.  Now it is recognised that this is counter-productive in terms of carbon storage / sequestration and biodiversity, so there are now measures to restore wetlands. The hope has been that restoration of wetlands will do much to restore the variety of plants and animals (and help carbon storage).  However, research by the University of Copenhagen suggests that such projects might be ‘struggling’. The study examined ten wetlands (near the River Odense) that were restored between 2001 and 2011.  The restoration involved the removal of drains and ditches, and allowed streams to meander again instead of flowing in ‘straight channels’.  The aim of the project was primarily to reduce the leaching of nitrogen and phosphorus from adjacent farmlands, and hope to see greater diversity of plants (e.g. marsh orchids, globeflower, tussock-sedge and ragged-robin).   The ‘restored’ wetlands were botanically poor (whether restored in 2001 or 2011), they had only a quarter of the plant species compared to natural wetlands.  This may be due to  the continued input of nutrients (from agriculture), which encourages species that are ‘nutrient hungry’ at the expense of others. the ‘difficulty’ of wetland species to disperse from one area to another. It may be that future restoration programs will need to include planting / seeding of additional wetland species. It has been suggested  that it could take the best part of a hundred years for the restored wetlands to resemble natural wetlands. Redwoods and relatives. Previous posts have talked about the special features of the giant redwoods (their height, age etc).  Over the last 150 years, they have ben subject to the pressures of commercial logging, clear felling and more recently high intensity fires.  Indeed, the fires have been of such an intensity that seed banks in the soil have been destroyed. Now they have been subject to genomic analysis, that is their DNA has been analysed and sequenced.  The first conifer genome to be sequenced was that of Norway Spruce, then that of loblolly pine.  These suggested that conifer genomes are large (3 to 10 times larger than the human genome), with repetitive sequences.  Coast Redwoods are hexaploid, that is, they ave six copies of each chromosome (we are diploid, that is, have only two copies of each chromosome).   The DNA of a coast redwood has  27 billion base pairs of DNA, the giant sequoia has 8 billion; by contrast we have circa 3 billion.   It is hoped that the Redwood Genome project will see the restoration of areas of coast redwood and giant sequoia that have been lost over the years. The genomic analysis will help inform and guide management strategies, ensuring genetic diversity in the newly planted tree seedlings. Such a strategy will (hopefully) enable newly planted areas to survive and thrive — in the Anthropocene. More on chromosomes Just as it has recently been shown that Coast redwoods are polyploids (i.e. have extra sets of chromosomes), so recent research in the Czech Republic has shown that the common nettle [Urtica dioica] has different ecological ‘preferences’ depending on its chromosomal status.  Nettles can be diploid (2n = 26) or tetraploid (2n = 52).  The tetraploid nettles seemingly have a broader ecological tolerance and a wide geographical distribution, whilst the diploid nettles occur in a narrower range of ecological conditions. Details of this research can be accessed here (note link opens a PDF) and Plants for a future has lots of information on nettles.    

Stinging nettles (Urtica dioica) are widespread across the UK.   They are found nearly everywhere; in woodlands, hedgerows, gardens and on disturbed ground. Nettles have been found in and around human settlements since the earliest of times; they probably formed part of the diet in Stone Age times.  Nettles also provided fibre for clothing.  A piece of nettle cloth has been found in Denmark's richest known Bronze Age burial mound (Lusehøj). It is associated with the burial of a rich and powerful man - after the burning of his body, his bones were wrapped in a cloth made from stinging nettles and then placed in a bronze container. Stinging nettle pollen is often to be found in soil sample cores, suggesting it is one of our native plants though human activity and movement may helped it to extend its range.  Nettles can tolerate a wide variety of soil conditions, though they seem to like moisture, and soils rich in nitrate and phosphate. In favourable conditions, they can grow to a metre or more in height. There are patches of stinging nettles that mark phosphate-rich debris from abandoned villages and sites of human occupation from more than 1500 years ago. Nettles have the potential to grow and expand in woodlands, perhaps aided and abetted by the increasing levels of eutrophication (nitrate / phosphate enrichment from air borne pollution).  Indeed, they can become 'botanical thugs' overwhelming other members of the ground flora  / herb layer. Read more...