In order to carry out an in-depth representation of the plants, while at the same time generalizing, the list of species is divided into functional groups that share a common adaptive property or groups of properties. In many French studies, such groups were titled: “groupes ecologiques.” Other researchers named such groups slightly differently, as “guilds.” We shall deal here with functional groups as they may be seen in the Negev, Sinai, and Edom (SW Jordan).
1. Shrub-steppe plants
Semi-shrubs growing all over the area surround the rock outcrop. Influenced by a high fluctuation in the mean annual rainfall quantity, the lithosol vegetation looks rather dull and gray even in the spring of a dry year (Fig. 3.1.15). In a rainy year, in the same area, with similar ground, the site looks like a multicolored flower garden (Fig. 3.1.16). The most common contributors to the phytomass of the shrub-steppe are Artemisia sieberi and Helianthemum vesicarium which has highly colorful populations in the Negev Highlands (Figs. 3.1.16, 3.1.17).
2. Plants of desert rocks
The following samples dealt with here are the most common inhabitants of desert rock vegetation. The class of rock vegetation in Israel is named Chiliadenus iphionoides (Fig. 3.1.18) and it dominates the rocks of the Mediterranean and the desert areas. It is assumed that in the desert, C. iphionoides receives the same amounts of water needed to sustain the plant in Mediterranean territory. It is accompanied by Stachys aegyptiaca (Fig. 3.1.19) and by many other species. Taxonomic investigations carried out in the Middle East prove the presence of closely related endemic species in the principal rocky terrain of Jordan, Israel, and Sinai. The forefathers of these species penetrated into the desert from the Mediterranean area, and after local speciation in the rock islands, remained as refugees in the large desert refugia until now. These processes resemble similar situations taking place in oceanic islands and are discussed under the theory of evolution in island research. In both cases the new species are isolated from their relatives.
3. Local endemic species
Local endemic plants displaying the island situation are a particularly clear phenomenon in the species of section Campanulatocalyx in the genus Origanum. O. dayi inhabits the largest area in this group (Fig. 3.1.27). Its noticeable adaptation to the dry climate of the area may be seen in the replacement of the leaves during the year. At the beginning of winter new branches sprout from the plant base carrying large winter leaves (Fig. 3.1.20). Small summer leaves develop later (Fig. 3.1.21) and the transpiring area becomes reduced. In the Negev Highlands (Fig. 2.1.22) a smaller area supports the species Origanum ramonense (Fig. 3.1.23), closely related to O. dayi. A similar situation may be considered with Origanum petraeum (Fig. 3.1.24) and O. punonense, which are confined to a small area in SW Jordan. Each of these Origanum species is endemic to a small area in the country of their discovery. Origanum isthmicum may be regarded as a “dot endemic” and shows in its morphology high affinity to three sections of the genus Origanum. This situation could serve as testimony for the “old age” of the species, which goes back in history to the time when the genus was not yet finally shaped. We do not have an evolutionary watch to evaluate this evolutionary time. The sixth species, Origanum jordanicum (Fig. 3.1.26), is a unique addition. It resembles Origanum isthmicum in its smell, in the leaves and small corolla, almost as small as the calyx. However, it differs from the entire genus by virtue of the deflexed calyx teeth.
The six species of the section were formed or survived in places (Fig. 3.1.27) isolated by large desert areas between them. They can serve as a good example of palaeo-endemism in “moist islands in the desert.” The four previous species, that do not have a scent of thymol and carvarcrol, have a corolla protruding from the calyx and anthers protruding from the corolla. The evolution of species in this section of Origanum may be divided into two prominent groups.
There are two Teucrium species in the Middle East with similar morphology. These are T. capitatum and T. leucocladum (Fig. 3.1.28, 3.2.29). A detailed study of the T. capitatum complex in Europe showed that the hairiness (indumentum) has an important set of diagnostic characters. After a comprehensive study of the T. leucocladum complex in Israel, Sinai, and SW Jordan, I recognized three subspecies of T. leucocladum differing in their indumentum (Figs. 3.1.30, 3.1.31). I decided to use the sub-specific rank following an article by Peter Davis regarding eight subspecies that are considered as “geographical races.” Two additional examples of isolated speciation are Micromeria serbaliana found in S Sinai and its relative M. danaensis endemic to Dana Nature Reserve in SW Jordan (Fig. 3.1.32). The second group is of Silene danaensis (Fig. 3.1.33), growing in SW Jordan, S. swertiifolia growing in the Mediterranean territory of Israel (Fig. 3.1.34), and S. libanotica (Fig. 3.1.35), growing on Mt. Hermon, S. Lebanon.