2 posts tagged with

rock whitebeam (Sorbus rupicola)

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Royal Botanic Garden Edinburgh (27th July 2008) Part 1: Sorbus arranensis and Sorbus pseudofennica

Well, I was down at Edinburgh's Royal Botanic Gardens on Sunday (third time that week) and it was a glorious day. I had myself a good time walking around in the sun admiring trees and taking several hundred photographs. My favourite bit of the Gardens is the Highlands area just on the left when you come in at the East Gate. Not because it is particularly well laid out, or that there are any especially interesting specimens in there, but because it is planted with the things that I am most familiar with and fond of: Scots pines, silver and downy birches, gorse, heather, bilberries (blaeberries), rowans, brooms, alders, foxgloves… These kinds of flora are familiar to me from trips to the Highlands, but mainly from living on the edge of the Peak District, where all of the above are abundant.

Anyway, three small trees in the Botanics' Highland bit specially caught hold of my attention after writing this recent post on Arran whitebeams. Two of the trees were Sorbus arranensis (a.k.a. Arran whitebeam); the third was a Sorbus pseudofennica (a.k.a. Arran cut-leaved whitebeam a.k.a. Arran service tree a.k.a. bastard mountain ash). Neither of the two species are found anywhere in the world except the Isle of Arran. Says the Forestry Commission:

Only a few hundred trees of each species exist, clinging perilously to the steep rocky slopes of two remote glens at the north of the island.

The Arran whitebeam was first recorded in 1897...

The other rare hybrid, the Arran cut-leaved whitebeam, was first noted in 1952. [...] Both species were more abundant in the past, but have been forced to retreat to their restricted enclaves as the island was progressively improved for agriculture.

small Sorbus arranensis

This is the smaller of the two S. arranensis trees. As you can see, it is only a young 'un.

leaves on the small Sorbus arranensis

And these are some of the leaves of the small S. arranensis.

larger Sorbus arranensis

This is the larger S. arranensis. A poor photo, but it gives an idea of the form.

 Sorbus arranensis leaves

Leaves from the top...

 Sorbus arranensis leaves

...and some from the bottom.

S. pseudofennica

The S. pseudofennica, squeezed in between a rowan and a birch.

S. pseudofennica leaves

S. pseudofennica leaves...

S. pseudofennica leaves

...more leaves...

S. pseudofennica leaves (undersides)

...and the silvery undersides of even more leaves.

I found a paper by Robertson, Newton and Ennos (my dissertation supervisor and one of my old lecturers) - Multiple hybrid origins, genetic diversity and population genetic structure of two endemic Sorbus taxa on the Isle of Arran, Scotland (Molecular Ecology (2004) 13, 123–134) – that clears up the origins of both of these Arran whitebeams. From the abstract:

In this study, we use an array of genetic markers in a population analysis to elucidate the hybrid origins of the Arran whitebeams Sorbus arranensis and S. pseudofennica, two woody plant taxa endemic to the Isle of Arran, Scotland. It has been proposed that S. arranensis was derived by hybridization between S. aucuparia [rowan] and S. rupicola [rock or cliff whitebeam], and that subsequent hybridization between S. arranensis and S. aucuparia gave rise to S. pseudofennica. Analyses of species-specific isozyme, nuclear intron and chloroplast DNA markers confirm the proposed origin of S. arranensis, and indicate that S. aucuparia was the female parent in the hybridization. Analysis of microsatellite markers suggests that there have been at least three origins of S. arranensis on Arran. Microsatellite markers also support the proposed hypothesis for the origin of S. pseudofennica, and indicate at least five hybrid origins of this taxon.

And from the Introduction, an explanation of the origins of S. rupicola, the subject of the last treeblog post:

...S. rupicola... (rock whitebeam), itself an autotetraploid derivative of S. aria [common whitebeam]. It is most likely that S. aucuparia was the female parent involved in this cross because S. rupicola produces seed apomictically, but has significant pollen fertility of 20%.

Being the kind and generous human being that I am, I have attempted to sum up all of that information in the following simplified graphic:

Arran whitebeams family tree (haha!)

Now, I think I'll end the post here. I have more material for a future post about whitebeams in Holyrood Park (again), but I think regular readers must be sick of Sorbi by now so I'll lay off 'em for awhile!

Bonus picture!


When I was photographing the S. pseudofennica this fly accosted my hand. So I took a photograph and was pleased to see what a big fly looks like from so close.

Posted in Miscellany

Rock whitebeams in Holyrood Park

rock whitebeam leaves

Rock whitebeam leaves; upper surface (left) and silvery lower surface (right).

Rock whitebeam (Sorbus rupicola) is a small tree endemic to north-west Europe. According to ukwildflowers.com, rock whitebeam is

Absent from the south east of England and central and Southern Ireland, the few trees which exist are scarce and slightly more frequent the further north you go.

Not so long ago I stumbled across this .pdf document which provides details of rock whitebeam and its distribution in Edinburgh’s Holyrood Park. The document, marked “Edinburgh Biodiversity Partnership”, is over eight years old now so I will take the liberty of plagiarising big chunks of its content:

Rock whitebeam is found on steep rocky slopes or cliffs of basic rock at low to moderate altitude. It often grows in inaccessible situations... Mature individuals readily produce flowers and fruit, the latter probably being distributed by birds in order to regenerate the species in new locations.

Rock whitebeam is apomictic, which means that it can produce viable seed without the need for sexual exchange as well as preventing the possibility of any crossing with other related species. Populations are often very small and it is quite common for single trees to exist in isolation.

Regarding Holyrood Park’s population, the document has this to say:

[Rock whitebeam] has probably never been common in Edinburgh, with numbers particularly declining since the turn of the century. Rock Whitebeam has been known from Holyrood Park since 1813…

Only one large ‘mother tree’ and one or two very young saplings remain on Dunsapie Crag with a further two or three on the rock face of Raven’s Crag west of Duddingston Loch. However, it is possible that there are still trees hidden away in one of its former sites or elsewhere.


Fire damage, both accidental and as a management tool, has probably had the single largest impact on the Edinburgh population of rock whitebeam. Rabbits are keen to eat the bark of the closely related rowan, and so it is likely that rock whitebeam has also been targeted. This may be the main reason for its occurence [sic] only in inaccessible places.


Although fire is no longer used as a management tool in Holyrood Park there is always the possibility of accidental fires being started. Indeed, the prevelance [sic] of fire may increase as gorse, which is highly flammable, is likely to extend its range as a consequence of the recent removal of grazing cattle and sheep from the Park and the fact that it is no longer collected for winter fodder.

Hearing that there were rare trees within a short distance of our flat, last Monday (July 21) I went on a mission with my flatmate and fellow ecologist to Dunsapie Crag to see a rock whitebeam up close. We were in luck: there were three of them at the Crag. There was a big one high up the rocky Crag face, which I presume to be the aforementioned ‘mother tree’; a smaller one beneath the ‘mother’ but still on the face; and a smaller one still growing in the grass beneath the Crag.

the ‘mother tree’

The ‘mother tree’.

the youngest rock whitebeam

The youngest rock whitebeam with Dunsapie Loch in the background. The leaves in the photos at the beginning of this post belong to this tree.

all three Dunsapie Crag rock whitebeams

All three Dunsapie Crag rock whitebeams.

We didn’t go and have a look for the rock whitebeams that the “Edinburgh Biodiversity Partnership” said were on the face of Raven’s Crag, but on the way back around the west side of Arthur’s Seat we spied a couple of young specimens just below the path.

two new rock whitebeams

Two more Holyrood Park rock whitebeams - new discoveries?

And coming in a future post… more whitebeam wonders at Edinburgh’s Botanic Gardens.

Book announcement: Between Earth and Sky: Our Intimate Connections to Trees, authored by Nalini M. Nadkarni, is a recent release by the University of California Press. Check it out here. UC Press have generously offered to send me a copy to review, so keep your eyes peeled for treeblog’s inaugural book review!

Posted in Miscellany

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