April 2018

At a recent Gardening Club meeting we were introduced to many rare and unusual wildflower species, including a few parasitic ones.  One feature that immediately sets wholly parasitic plants apart from other plants is that they don’t contain chlorophyll, the substance that gives plants their green colour and is responsible for photosynthesis which allows them to convert the sun’s energy into growth.  (Note that there are many semi-parasitic plants like mistletoe and yellow rattle that do contain chlorophyll which means that they are less of a drain on their hosts.)

Toothwort (Lathraea squamaria) was the first plant mentioned.   This plant may be found in Alexandra Park where I have seen it growing in the undergrowth below some of the trees there.  Because it contains no chlorophyll, it doesn’t need a sunny spot to thrive, just as long as its host gets plenty of sunshine, though it does need to attract pollinating bumblebees which it does mainly by scent.  It invades the roots of trees and spends most of its life underground, only sending up the flower spikes in early summer.  It has an underground network of rhizomes which have pad-like tips (called haustoria) that attach to, and penetrate the bark of the host roots to get at the nutrients within.  The whole of the plant, including the underground parts are a pale creamy white.  It is not clear whether it gets its name from the resemblance of the flowers to a row of teeth or from the tooth-like scales on its roots.  Like all plants whose name ends with –wort, it was used medicinally for toothache, based on the doctrine of signatures.  It wasn’t commonly used, however, due to the plant’s relative scarcity.

Another parasitic plant mentioned was common dodder (Cuscuta epithymum), a member of the convolvulus family.  I know dodder from Dungeness Nature Reserve where it parasitizes wood sage.  It takes a different approach to toothwort in that its life cycle is completely above the ground.  When the seed germinates, it produces a root-like shoot that must find a host quickly before the energy contained within the seed is exhausted.  Once it has found a host, a sucker develops from which a thread-like stem grows which twines around the host stem (always anti-clockwise, or widdershins as we used to say before clocks were invented) and haustoria in the sucker and stem penetrate the host’s stem to extract nutrients. The root-like shoot then dies off.  As it nearly always kills or at least severely weakens its host, further stems reach out to neighbouring plants until a fine network of dark red stems cover a sizeable area.  It has no leaves because, like toothwort, it has no chlorophyll, taking all the energy required for growth from its host plant.  Small clusters of flowers form along the stems and produce seeds for the next generation.  The seeds can lie dormant for many years and it seems to favour disturbed ground, making it a common plant of managed heathland.  Dodder has also been used in traditional medicine as a purgative and for liver disorders.  Though native to Europe, it is now found on six continents; its spread is thought to be due to exported forage.  

The third parasite mentioned was a bit of a surprise as I was not aware of a parasitic orchid.  The bird’s nest orchid is another parasite that does not contain chlorophyll and this plant is a real specialist.  It parasitizes a fungus Rhizoctonia neottiae that is only associated with beech trees.  It is probable that the fungus has a symbiotic relationship with the beech trees, and it is also possible that the orchid provides some nutrition to the fungus via its roots which mesh with the fungal threads.  Apparently in Finland it is one of three different orchids without chlorophyll that are not related and are believed to have developed the same life cycle independently.  After flowering, the orchid and its rhizomes die off leaving only the tips of its roots which then grow into new orchids. 

March 2018

I have heard that grass doesn’t grow when the soil temperature is below 6 degrees C.  It is quite irritating then to find that despite the cold and dull weather that seems to have persisted for weeks, that our lawn needs mowing.  It’s even more irritating that it’s too cold and wet to get out there for the first mow of spring.  Grass is always a chore for gardeners, if it’s in the border it needs weeding out, if it’s not it probably needs mowing.

Unidentified, possibly Sweet Vernal Grass

It may however, be worth pausing as you empty the grass box, to marvel at one of nature’s most successful plants.  It grows just about everywhere from the high tide mark to well above the treeline and from the tropical rain forests to all but the driest deserts.  It comes in many forms – as grasses, sedges, and rushes, and even bamboo.  Incidentally, grasses, sedges and rushes are in separate families – Poaceae, Cyperacae, and Juncaceae respectively – and if you are not sure which is which then you need to remember the rhyme, ‘sedges have edges, rushes are round and grass stems are hollow right up from the ground’.  (That refers to the flowering stems which are triangular in the case of sedges.)  If you choose a grass species with fat seeds and fill a field with it, then you will have part of the world’s staple diet.  Where would we be without wheat or rice, or my own particular favourite, barley? (roasted and suitably mixed with another favourite native plant species Humulus lupulus, better known as the common hop.)  Another large part of our diet (too large in many cases) is derived from yet another grass – sugar cane.

Canary Grass

There are more than 10,000 different species of grass worldwide, and it is likely that your garden, however tidy you keep it, will contain a dozen or more different ones.  Identification of grasses is not easy and requires a lot of time looking for identifying features and following keys.  The botanical language used is different to that used for other plants because grasses have things like awns and stipules and spikelets that other plants don’t have.  Of course, the first thing you need to do to identify any type of grass is to stop mowing it and let it flower.  Grasses are wind pollinated and so they don’t need showy scented flowers to attract insects.  This means that the flower features are quite small and a hand lens is useful to see them clearly.  I have managed to identify a few species in our garden – Sweet vernal grass, which gives new mown hay its sweet smell, Quaking grass, Cock’s Foot, Field Wood-rush (a small but pretty species), Perennial Rye grass, and of course Common Couch grass.  Yet another species that I am trying to eradicate is Pendulous Sedge – if you have any, I recommend that you don’t let it flower!

Unidentified, possibly one of the False Oats

I find that the names of grasses have a sort of ancient and romantic feel to them.  Things like bents and fescues, crested dog’s tail, wood melick and canary-grass.  Believe it or not, there’s even one called Timothy.

Field Wood-rush