Allopatric Distribution of Two Varieties of Medicago Laciniata (L.) Mill. in the Negev Desert

Abstract

Medicago laciniata (L.) Mill. is a winter annual represented in the Negev by two varieties: M. laciniata var. laciniata and M. laciniata var. brachyacantha Boiss. The first variety has larger pods with markedly longer spines (Fig. 1) and occurs in relatively less arid habitats (Heyn 1963). In the Negev, near Sede Boqer (300 52' 49 N, 340 51' 27 E), it occupies northern slopes and wadi beds dominated by the association of Artemisietum herbaealbae (Zohary 1962; Friedman 1969). The second variety occurs in more arid habitats, such as southern slopes and hill tops dominated by the association of Zygophylletum dumosi. Thus, the populations of the two varieties occupy distinct adjacent territories and meet along the base of the southern slopes where intermediate forms occur within a narrow strip (Fig. 2). Rodents and ruminants are common in the area and are capable of carrying the spiny pods tangled in their fur from one slope to another. Seeds are also dispersed by these animals through their faeces since a few at least remain viable after passing through the ruminant digestive system. Seed longevity of both varieties is considerable. Germination of 20-year-old seed was tested and was found to be 8500 after 48 h. The aim of the present study was to investigate the factors controlling the distribution of the two varieties. The growth, development and yield of each variety was evaluated under the relevant environmental conditions with and without the effect of the associated plant communities.