Morphology of Pinus uliginosa (Pinaceae) needles from populations exposed to and isolated from the direct influence of Pinus sylvestris

Eleven needle traits of two contrasting populations of Pinus uliginosa (P. mugo complex), one located in a Pinus sylvestris forest, the other isolated from the influence of this species, were compared to quantify the degree of hybridization. Statistically significant differences between the studied populations were found, but both of them differed by a similar degree from P. sylvestris. Surprisingly, the R uliginosa population surrounded by the P. sylvestris forest, which was expected to consist of individuals with intermediate traits, appeared to be more closely related to R mugo than those isolated from the direct influence of R sylvestris. Large differences in the distances between the analysed pair of populations of R uliginosa and R sylvestris have not influenced the morphological traits of the species. Gene flow from P. sylvestris to R uliginosa is possible, but is likely to be small and does not differ compared with populations of P. uliginosa. The decline observed during the last three decades in both populations of the species has not influenced their needle morphological traits. (C) 2003 The Linnean Society of London.