February 2018

I like writing this column because it forces me to check my facts before I write it and that means that I find stuff out.  We had some unusual visitors to our bird feeders recently – redpolls.  This was very unusual simply because we have never seen them on there before.  Redpolls are a small finch that breeds in this country, and we also get an influx from Scandinavia in winter.  When I looked up redpolls, it turns out that they could have been one of two species – the common redpoll, or the lesser redpoll.  Apparently these have only recently been split into two species, more recently than 2001 when my bird guide was published.  My bird guide did however, mention two sub-species depending on where in Scandinavia they bred, that correspond to the new species division.  So did we see Lesser Redpoll or Common Redpoll?  I haven’t a clue because the differences are small (one is slightly smaller and paler than the other) and I wasn’t expecting there to be two possible species when I saw them.  But it was a delight to see them and as long as they know the difference that’s all that matters.

Common or Lesser Redpoll - Carduelis flammea or cabaret

In last month’s column I briefly mentioned mosses and liverworts.  Apart from the fact that I could probably point out mosses or liverworts if I saw them, that was about all I knew, so I looked them up and it turns out that they are a very interesting group of plants.  As a group they are known as bryophytes and the group includes another set of plants that I had never heard of – hornworts.  Apparently hornworts are quite scarce in the UK which is probably why I haven’t come across them before (and if I had I probably would have thought them to be liverworts).  One thing about bryophytes is that they are not vascular plants.  Vascular plants (the plants we are more familiar with) have flowers, branches, and even trunks that contain sap which flows through the plant in a similar way to blood in veins – hence the term vascular.  Vascular plants grow, flower, set seed, which then germinate to form new plants, but bryophytes complicate matters with an extra stage. 

Bryophytes produce spores; those spores, usually dispersed by the wind, land somewhere favourable and grow into a new plant, but the difference between spores and seeds is that the DNA in seeds has the chromosomes from both parent plants, but bryophyte spores only contain the DNA from one parent.  (The technical term is haploid.)  When the plant that grew from the spore grows into a moss or liverwort, that stage cannot then produce spores.  Instead each plant is either female which produces eggs, or male which produces sperm.  The sperms are then usually dispersed by water (which is why bryophytes usually grow in very damp places) or by insects that carry sperm from one plant to another.  This egg and sperm stage is called the gametophyte stage, but you probably don’t need to know that.  The fertilized eggs are then dispersed from the gametophyte, again usually by water and having both the male and female DNA, they can then grow into the spore producing generation (called sporophytes, should you be interested).

From studies of their mitochondrial DNA it has been suggested that liverworts may well have been the first land plants to evolve from green algae more than 400 million years ago.  There are thought to be more than 1,000 species of bryophytes found in the UK and more than 20,000 worldwide. Though they are often overlooked, mosses and liverworts are an important part of the ecology and support a wide range of insects and other arthropods, not to mention the many birds that feed on those smaller creatures.  One day I hope to find a creature that makes its home only in moss – the tardigrade bear – that is almost microscopic and not actually a bear, but no less interesting for all that.