Near Zadar, Croatia, grows an oak which is different from other local oak species in the neighborhood; Q. x viridis Trin., called "green oak". To clarify the origin of this tree we investigated the anatomy of wood an leaves (in particular, the hairs and epidermis cells were examined). The investigations' were done with different methods: light and scanning electron microscopic (high vacuum and ESEM) techniques combined with digital image analysis. We compared the results of the wood anatomy with the results of Q. cerris, Q. ilex and Q. pubescens in the neighborhood and in literature. Q. cerris, Q. ilex and Q. pubescens are supposed to be the ancestors of Q. x viridis. Investigations of the leaves were done with Q. x viridis, Q. cerris and Q. ilex. A number of measurements and histochemicals reactions were done with the epidermis, hair, and root meristem-cells. EDX was used to determine the elements in the hairs, and the DNA-content of the nuclei was measured using Feulgen-reaction in combination with a densitometric method. The woods of Q. x viridis, Q. cerris, and Q. pubescens are ring-porous, Q. ilex is diffuse-porous. Of the whole rays the anatomy of Q. x viridis and Q. cerris is very similar, triangular ray cells were only seen in preparation of these trees. Q. x viridis has five different types of hairs, the other investigated oaks only four. Q. x viridis and Q. cerris have a similar number of hairs on the adaxial suface of the leaves. The numbers of hairs on the abaxial surface are different, Q. x viridis has less hairs. The sizes of the hairs of Q. x viridis and Q. cerris are similar. We found lipoids and cuticle in all hairs, only the cell walls of the hairs of Q. x viridis are slightly woody. EDX analysis shows no flint or lime. DNA measurements show contents of 1.2 pg for 2 C nuclei of Q. x viridis, Q. ilex has 1.4 pg (root meristem). The majority of the nuclei of hair cells have a DNA content of 2 C (all investigated oaks), some of them 4 C and 8 C (Q. cerris). The Nuclei of epidermis cells have DNA contents up to 16 C. The results of this investigation and the origin of the "Green oak" will be discussed.
