Florula Urbana: what whitebeam is this?

I saw this sapling yesterday, and identified it on the fly as Swedish whitebeam (Sorbus intermedia).

Having looked more closely I'm not so sure. Some of the leaves have free leaflets at the base, and the number of lateral veins seems to be on the low side. But the overall shape of the leaf doesn't match bastard service tree (Sorbus ×thuringiaca). The nearest match in Stace, for leaf outline, seems to be Swedish service tree (Sorbus hybrida). But all this analysis assumes that the foliage of young plants looks the same of that of mature plants, which I don't know to be the case.

Any ideas? (Am I right in identifying it as a whitebeam, or have I missed something that should be obvious?)

Update: 14 June 2008

I was passing the area again today, so I had another look. This plant is growing in a grassy verge in an industrial estate, in front of a row of conifers (leylandii?). There are several other shrub seedling growing there - a cherry, a rowan, an elder, some hawthorns, a couple of cotoneasters (I think that they are C. microphyllus and C. simonsii), and a couple of specimens of another whitebeam (but apparently not Sorbus aria). I suspect that the conifers are a bird roost, and this explains the appearance of seedlings of berry bearing shrubs and trees adjacent to them. (There is a nearby patch of woodland, but this doesn't contain any immediately visible Sorbus; the commonest tree there is alder (Alnus glutinosa) and there are a couple of laburnums.

This is a leaf of the sapling. This particular leaf has one pair of free leaflets at the base, but the on the sapling the number of free leaflets at the base varies between 0 and 1. Note that the number of lateral veins is about 8 per side.

This is the other type of whitebeam. (Is it Sorbus latifolia?)

These are the other shrub seedlings

About a mile to the south I came across a group of about a dozen of what seems to be the same plant, near to a country (urban fringe) lane. I can't tell whether these are spontaneous, or planted. There are planted trees in the area (oak, ash, birch, lime, cherry), but these whitebeams aren't obviously of the same vintage. One or two of them are fruiting. These have 1 or 2 pairs of free basal leaflets, sometimes 0.

Here are some photographs.

To add to the complexity at the end of the lane there's a small group of houses with 4 whitebeams (unlobed leaves, distinct white meal on upper surface) which appear to have been grafted onto the species under discussion (3 of those 4 whitebeams are suckering). The leaves of the stock sometimes, but not always, have pairs of free basal leaflets.

I see no reason to suspect that these aren't Sorbus aria. One wonders why this is grafted on a rarer species. Perhaps it's an import from a country where it isn't rarer. Perhaps it's intended as a dwarfing rootstock.

The scion.

The stock.

Between the two sites, where a bridge crosses a dual carriageway that has been driven through a cutting, the banks of the cutting have been planted with a variety of trees, incluing two types of Sorbus. One is a whitebeam rather like the last, while the other is darker leaved. Using a digital camera as a binocular substitute tells me that the latter is Sorbus intermedia.