Effect of Climate in Seed Diversity of Wild Tunisian Rhus tripartita (Ucria) Grande

Rhus tripartita (Ucria) Grande (Anacardiaceae) is a rare and endangered species. Seeds of Rhus tripartita were obtained from spontaneous populations in nine different localizations in Tunisia and their shape analyzed by image analysis. Seeds were harvested in 2014 and image analysis was done in CSIC laboratories (Salamanca, Spain).

The method for seed shape analysis is based on the comparison of seed images with a cardioid. Five hundred and thirty seeds from nine natural populations in Tunisia were analyzed giving percentages of identity with a cardioid (J index) ranging from 76.2 to 95.3. Variation was higher in the side of the seed containing the micropyle (right side). Seeds are classified in four types: A, B, C, or BC depending on their degree of similarity with the cardioid in both sides (right and left). Type A seeds have high degree of similarity on both sides; type B have high similarity in the right and low in the left; type C present high similarity in the left and low in the right, and finally type BC with low similarity value in both sides. Size and shape were compared for seeds in and among populations. Differences among populations were found both in size as well as in shape (roundness, J index total and partials). The analysis of seed size and shape reveals differences between climatic regions. The largest seeds are found in the lower semi-arid region; the smallest in the upper arid; in the lower arid, seeds are of intermediate size. Four morphological seed types were obtained (A, B, C and BC). Type A represents seeds in the lower semi arid climate whereas type C represents seeds in the arid climates.

Morphological types were characteristic for some of the populations indicating that differences in shape are independent of size Genetic and ecological effects contribute to seed size and shape of Rhus tripartita.