non je suis géologue, en revanche, il vous faut un biologiste végétal

It is very difficult to identity a plant merely on the basis of leaves. Flowers and fruits are must for correct identification.

I agree with Arvind, but I'll try.

A - Ailanthus altissima;

C - some kind of Fraxinus; (excelsior/pennsylvanica);

H - Acer negundo.

Dear Ana

 The Image A is of - Ailanthus probably and the image H is Acer Species probably, I will be very happy if my assumption is correct. herewith I also requiest you to do not collect such incomplete specimen without flower and fruit which is not identifiable.

with regards

Sunit Mitra

@Lukas Petrulaitis, @Sunit Mitra thank you very much for the  scientific name of the trees. Are very useful for me. I think also that A is Ailanthus altissima and C is Fraxinus. 

Thank you for the support ! 

A: I am quite sure that this is not Ailanthus altissima. Neither shape of the base of the leaflets nor their serrate margin fit for this species. E seems to be the same species.

B: Koelreuteria paniculata (Sapindaceae)

C/D: Some Fraxinus, most likely Fraxinus pennsylvanica.

H: Looks like Acer negundo.

Regards

Franz Starlinger

OK for Koelreuteria as B

Where are these tree growing. They look planted ornemental, arent't they ? The photographs are not enough to determine safely species.

@Marc Philippe your are right that these trees are ornamental. I have photographed these in a park from a church. 

Dear Ana-Maria,

"By their fruits ye shall know them", as my Botany Professor used to say. Do these leaves have a rank smell? Reproductive structures are the best way to positively ID a tree or plant.

SIncerely,

Amy

@Amy Eisenberg, the trees had no fruit and no flowers. I took pictures to identify them. It was the only solution.

In my opinion, A and E are Juglans nigra. The leaves are missing the terminal leaflets, which is normal in J. nigra. Also the serrate margin fits well.

Regards

Franz Starlinger

@Franz Starlinger the fruits of Juglans nigra (photo A and E) was like in the attached photo. 

Yes, of course. It should be clear now, that this is not Ailanthus.

 @Franz Starlinger, I must say that A and E are not the same tree leaf. The photos are  taken from different trees. 

@Arvind Singh @Dipti Das  you could help to identify the species [B, C, G, H] ? 

C,D are Fraxinus spec. Cf. americana.

Dear Colleagues

"By their fruits ye shall know them." Examining plant specimens with reproductive structures are the best way to identify plants to their respective specific epithet.

Sincerely,

Amy Eisenberg, Ph.D.

Ethnobotanist

On the third photo, as seen by the fruits - Ash (Fraxinus sp.), the seventh - Ivy (Hedera sp.).

B. Koelreuteria paniculata?

C and D. Fraxinus sp.

G. Aleurites molucana?

H. Hacer negundo?

Best wishes

A - Juglans nigra

B - Koelreuteria (may be) paniculata

C - Fraxinus sp.

D - F. excelsior

E - ?

F - Platanus orientalis

G - precisely NOT Hedera (for I am dealing with this genera)

H - (looks like) Acer negundo

With best wishes

Imag A & B : Species Ailanthus....

Imag: G: Sterculia or Jatropha.....

It is very difficult to identity a plant merely on the basis of leaves. if you taken flower or fruits..upload img....

It is not easy to identify only with pictures of leaves, it was important other featureslike flowers, fruits, an overall picture of the plant and the location.

The images, I think

A - Juglandaceae Family ?.

B -Koelreuteria paniculata?

C -Fraxinus sp.

D -Fraxinus sp

And -Family Juglandaceae.?,

F - Platanaceae family. Probably Platanus orientalis?

G- Brachychiton or Aleurites Moluccan?

H -Acer negundo?

 It is very difficult to identify only using leaves (vegetative organs). You may to employ other taxonomic features like flowers, fruits and seeds.  

"By their fruits ye shall know them."

Book Aymara Indian Perspectives on Development in the Andes

Approach the Botanical survey center existing in your country with the different parts of the plants. Refer International Plant Research Centers Directory too

Indeed, very difficult. 

I propose also Koelreuteria paniculata for B and Platanus for F (but rather other species than P. orientalis).

A - Pterocarya fraxinifolia

B - Koelreuteria paniculata

C - Fraxinus sp.

D - Fraxinus sp

E - Ailanthus altissima

F - Platanus x acerifolia

G - Paulownia tomentosa

H - Acer negundo

It is not that easy identifying trees from leaves alone, particularly if you do not show how the leaves are attached to the stems. The identifications above are mere guesses, but these are plants frequently found planted (and naturalised) in Bucharest.

Confirming Koelreuteria paniculata for B (unmistakeable at least among temperate zone trees - the leaflets look like they are falling apart), Platanus for F and Acer negundo for H. 

Dear Colleague, 

Do you have reproductive material to accompany your images of leaves and leaflets for a more scientifically correct ID?

A Ailanthus 

B Koelreuteria paniculata

C Fraxinus ? pensilvanicus

D ? Fraxinus

H Acer negundo

By their fruits ye shall know them. How about photographing reproductive material for a more positive ID?

http://www.aznps.com/rareplants.php

From where are these photographs and any hint on their local names?

I agree with Lukas Petrulaitis

Definitely:

A - Ailanthus altissima;

H - Acer negundo.

And:

C D - some species of Fraxinus (excelsior, pennsylvanica);

Yours respectfully

One would need additional details like floral structure, fruit and bark characteristics, and an appropriate family key in order to determine the exact identity of the trees.