Tuesday, 19 July 2011


Here’s one for all you fans of the counter-intuitive!

Stonecrops (Sedum sp.) are plants with hairless, succulent, fleshy leaves. These leaves act as water storage organs, hence Stonecrops are adapted for life in dry, sharply-drained environments (sand dunes, rocks, walls etc.). So the odd thing is that three of the Mersey Valley species grow on the river bank, almost at the water’s edge.

The explanation for this, superficially odd, circumstance is that the dry habitats, free from the competition that these small plants would have difficulty coping with, are at the river’s edge.

In some places sandy silt has built up to form miniature sand banks and in others the river banks have been shored up with concrete strips and rafts. These represent almost ideal habitats for Stonecrops, with one small snag, which you may be able to guess – but more of that later.

The three species are as follows:

Biting Stonecrop (Sedum acre) – Top Photo

This yellow flowered species is native to the UK. It is the first of the three species under discussion to flower (May to July). The leaves have a peppery, ‘biting’ taste – hence the name (it’s probably not wise to consume any more than the absolute minimum if you decide to test this out).
Biting Stonecrop is relatively common in the UK – usually on walls, rocks or sand dunes. Nevertheless, it is now rare in the Mersey Valley. The plants in the picture were photographed, just below the Princess Road Bridge, on a sandy layer deposited by the river on a concrete raft.

This species used to grow at the base of the brick walls that line the old sewage works channel that runs parallel to the river bank at the edge of Chorlton Ees. Sadly this population was destroyed a few years ago in a ‘tidying-up’ operation. When I complained I was told that it was, “only a garden escape”. This may or may not be true but garden escapes which become naturalised in the wild (and are not invasive) are intrinsically interesting and should not be carelessly destroyed – particularly not for reasons of tidiness!

I can’t find any old records, for this species, from Chorlton and adjacent areas but, in the mid-19th century, the species was certainly present in the Altrincham/Bowdon area.

White Stonecrop (Sedum album) – Middle Photo

This species is also native to the UK, but is restricted in its distribution as a truly native plant. Nevertheless, it is not infrequently encountered as a naturalised garden escape. It flowers from June to August.

White Stonecrop is now, by far, the commonest Stonecrop on the narrow strips and rafts of concrete at the river’s edge. A couple of weeks ago its massed flowers made a spectacular display at the base of the northern river bank about quarter of a mile west of Crossford Bridge - which carries the A56 over the river near Stretford. I noted some small butterflies feeding on the flowers. There’s one of these butterflies in the photograph. I think that it’s probably a Small Copper (Lycaena phlaeas) – but feel free to disagree with me!

Rock Stonecrop (Sedum forsterianum) – Bottom Photo

Rock Stonecrop is another native plant which also frequently occurs as a garden escape. It’s much less common than White Stonecrop and much more sporadic in its occurrence, but grows in much the same places. It flowers from June to August.
It is generally larger, has much longer slimmer, pointed leaves which are flattened on their upper surfaces.

The snag for these plants is, of course, that periodically they have to endure flooding. You’ve probably seen the Mersey in spate – a rushing, raging torrent which can rise right up to the upper flood banks, completely inundating the Stonecrops’ habitat. It’s amazing that they don’t get washed away – they must have amazingly strong root systems!

What I suspect actually happens that many leaves do break off and are washed downstream. Then, if luck prevails, they will end up on another bit of concrete where they can produce roots and another Stonecrop colony.

Dave Bishop, July 2011

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