May 2018

I hesitate to say it, but I think spring is finally here.  There are cowslips in flower at the end of Pett Road where it joins Rye Road; there are wood anemones and lesser celandine all along Rosemary Lane, and there are bees feeding and nest searching in our garden.

Buff-tailed Bumblebee - Bombus terrestris

Two species of bee have particularly caught my attention – the buff-tailed bumblebee, and the hairy-footed flower bee.  The buff-tailed bumblebee can hardly fail to grab some attention.  For a start, it is Britain’s largest bumblebee so the queens are really easy to spot.  If that doesn’t get your attention then the deep throaty buzz of its wing muscles certainly will.  There seem to be a lot more queens about this year.  Maybe that is because the difficult spring has delayed their emergence from hibernation, or perhaps they had a successful year last year meaning that more queens went into hibernation and, being well fed, more survived hibernation.  Hopefully that’s a good sign for the coming season.

Hairy-footed Flower Bee, female in unusual pose, tongue out and
grasping the leaf with her mandibles

The hairy-footed flower bee could easily be mistaken for a small bumblebee, particularly the females.  It is a solitary bee (which means it doesn’t form colonies) and the male and female are very different.  The female is completely black except for some orange hairs on her hind leg, whereas the male is smaller and mostly ginger.  One thing that sets them apart from bumblebees is their habit of hovering and darting around flowers, so if you see what looks like a small black bumblebee hovering by your flowers, it has probably got hairy feet.  (That’s not actually true because it is the male that has the noticeably hairy feet that gives the species its name.)  Just like bumblebees they love the flowering currant and dwarf comfrey that are in flower in our garden at the moment.

But to go back to the cowslips at the end of Pett Road – I’ve never seen them there before, or at least never noticed them there.  This may be because of seed quiescence or seed dormancy.  Seed quiescence means that the seed is too cold, too warm, or too dry to germinate so it will wait until conditions are right.  Also, it may not be in the plant species best interest for all seeds to germinate at the same time – some flowering earlier or later may make a better use of available resources, or maybe flowering next year would be better.  But seed dormancy is slightly different.  Some species coat their seeds with a tough waterproof coating which seems an odd strategy at first when seeds need water to germinate.  One reason this happens is to stop the seeds germinating in late summer or autumn which would mean that the plant wouldn’t survive to set seed.  The frost will shift the soil around the seed and grate away or soften the seed coating so that water can penetrate, at which point the seed is ready to burst forth when spring finally arrives. (The technical name for this process is stratification.)  If there is no frost or the seed is too deep, then seeds may stay dormant for many years until conditions are better for them.  Gardeners wanting to short cut the process have been known to resort to the freezer and sandpaper to get their seeds to germinate.  It makes me wonder how coconuts manage!

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.