Identification: Sichuan maple identification

Can anyone help me ID these maples photographed in Sichuan in September and October?

#1 is from Luoji Shan in S Sichuan, between 2500 and 3000m altitude.

 

#2 is from Hailuogou, WC Sichuan, 3000m

 

#3 is also from Hailuogou, WC Sichuan, 2500m

 

...and the last one, #4, also from Hailuogou at around 2500m.

 

Looks like they're Sec. Macrantha maples, specific anatomical features are used to determine which particular ones.

http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=317203

 

The trunk with the reddish papery bark belongs to a birch. One seen in western cultivation with a similar appearance is

http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200006168

 

Thanks Ron, I suspected they would prove difficult if not impossible to positively identify...

 

Are you sure? I'm almost positive it belonged to that maple.

 

Certainly looks like a birch, probably Betula albosinensis, to me.

 

Sorry, had another look at the full size image, and I guess you're both right, I had to do some acrobatics to get the pictures (and a few seeds), so must have missed the obvious.

 

Any idea what section this belongs to? Also Hailuogou, around 2500m. (Sorry for the quality, it was raining.)

 

Probably Section Palmata, Series Sinensia.

 

I had a similar thought but wasn't originally sure enough of myself to post. Acer sinense (A. campbelli subsp. sinense), for example, looks similar and is native to Sichuan at 2500m. (Not saying it is this species, just putting it forward as one possibility.)
A. sinense at Flora of China
Illustration

 

1,2=acer davidii very similar, is native of Sichuan, the last pic i agree with maf

 

The page I linked to the first time says 13 Sec. Macrantha maple species occur in China.

 

Thanks guys, it's all noted down on the labels :) Are there maples of sect. Sinensia that are reliably hardy in a (cool) maritime z7?

...and these can be whittled down further if the listed distributions are to be trusted: AA. davidii, forrestii, laxiflorum, maximowiczii, pectinatum. #1 and #2 were both shrubby, #2 was rather compact as well, but it was growing rather exposed.

 

Trees growing in a shrub-like manner a function of site conditions. Subalpine fir, for instance can be a 100' spire or a creeping mat.