Variability of leaf stomatal density of adult trees ofArgania spinosa(L.) Skeels in the field

Stomatal density is recorded on both faces of the two types of argan (Argania spinosa (L.) Skeels) leaves (simple and grouped) of 30 adult trees within three populations at Ait Melloul, Ait Baha and Argana, three sites in the south-west of Morocco, during three consecutive years, 1994–97. No stomata are observed at adaxial leaf surface characterizing argan as a hypostomatous species. Stomata density varies from 312 to 50 stomata per mm2 for simple leaves and from 294 to 62 stomata per mm2 for grouped leaves setting a large variability interval within argan populations. Tree genotype and its interaction with year are the sole significant sources of variation for simple or grouped leaves. Interpopulation (population) contribution to total variance is lower than intra-population (tree/population or its interaction with year). Repeatability (an estimate of broad sense heritability) values, 26.7% −38.3% for simple leaves and 18.1 to 46.1 for grouped leaves are relatively high within each population for this ecophysiological character.