Life-forms and Chorotypes of Succulent plants of Al-Dale'a Governorate, Yemen

The present study was carried out during the years 20152019, deals with the floristic composition of the flora, life forms and phytogeographical affinities of Succulent plants of Adhale Governorate, Yemen., The succulent flora of the study area consisted of 104 succulent taxa belonging to 52 genera and 29 families. Life form of study area, was dominated Chamaephytes with the maximum number of species they were represented by 46species (44.23%), followed by Phanerophytes represented by 29 species (27.88%), Geophytes represented by 13species (12.5%), Hemicryptophytes represented by 9 species (8.65%) Therophytes represented by 6 species (5.7%) and 1 parasite (0.96%). From the chronological point of view, the largest proportion of the succulent flora belongs to Monoregional constituting 77.8% (81) of species is native to the SudanoZambenzian phytochoria. The second dominant phytochoria was Bi-Regional constitute (11.46 %) "Sudano-Zambenzian + Saharo-Sindian (11 sp. 10.5%) and Sudano-Zambenzian + Mediterranian (1 sp., 0.96%), while Plueriregional comprises (11sp.; 10.57%) "The Tri-Regional element "SudZam +Sah-Sin+ Med, 3 sp. Cosm. 5 sp.; Trop. 2 sp.; Pan. 1 sp. Results also revealed that 41 taxa (39.4%) are endemic, (among them are 21 taxa (20.19%) which were endemic to Yemen alone, while the remaining (19.23%) are near endemic.

The present study aims at carrying out a comprehensive survey of the natural succulent flora of the study area, as well as analyzing the floristic composition. Furthermore, an annotated checklist is given in a step towards a thorough understanding of the succulent flora of Yemen.

2.Materials & Methods
The field studies were carried out through several trips during the different seasons in the period 2015-2019, in order to study the succulent flora of the Al-Dale'a governorate. The specimens collected include flowers and fruits, in addition to the leaves and stems (plants of small or moderate size, herbs and small shrubs), which were dug up carefully and the complete plant collected , included the underground succulent parts (roots, rhizomes, tuber and bulbs). The plant specimens were pressed during the field trip and transported to be preserved and mounted on a herbarium sheet. Another taxa were cultivated in our Botanical Garden at home as: Euphorbia, Aloe, Kalanchoe, Dorstenia. Plectranthus, Huernia, Monolluma, Orbea , Cissus etc., while flowers of stapeliads were treated with interest by keeping them in dark plastic bottles containing preserver solution which composed of formalin, glycerin and distilled water (3:1.5 : 30 ml) respectively.
The collected plant specimens were undergone to identification to species, subspecies, and variety level with the help of available literature. ( Plants species were classified on the basis of life forms as defined by Raunkiaer (51) and Hassib (38), determined the phytoclimate of the area . The chorology of the recorded taxa was retrieved from the literature (

3.Results&Discussion:
Analysis of Succulent flora: According to Kent and Coker (41), the main purpose of studying the vegetation is to know the dynamic and to develop strategies to protect species (34).
Succulent life forms of Al-Dale'a are a prominent feature and unique that reflects the shaping climatic, biotic, soil and topographical features of the study areas. The present results revealed that the study area comprised of 104 succulent taxa belonging to 52 genera and 29 families (Appendix 1).The enclosed appendix includes a checklist of all species collected in Al-Dale'a Governorate, which displays the related information on their life forms and chorological types. From the recorded 29 families in the present investigation there are 10 families 13 genera and 21 species of monocots, while dicots comprised 19 families, 39 genera and 83 species. At the level of species, Monocots are represented by 21 (17.2%) and Dicots by 83 (82.6%).From the present results, the largest succulent families of the monocots were Aloeacea (8 sp. , 1 g.). while dicots were: Apocynaceae "the largest and most diverse family with 33 sp. , 14 g. constituting 31.7% (33\104) of the total recorded species are including 2 subsp and 3 variety follow it Euphorbiaceae (8 sp. , 1 g.), Crassulaceae (6 sp. , 3g), Asteraceae (5 sp. , 3g) and Lamiaceae (5 sp. , 1g). Regarding the number of taxa belonging to these families, our results is agreement with (15:30:35).These six families constituted about 57.6% 60\104 of the whole succulent species of the study area.
The analysis of the present data has showed that, there are six genera that have the most number of species, represented about 57.6% 60\104 of the whole succulent genera of study area, Apocynaceae has been the largest number of genera which constitute 26.9% (14\52) and species which constitute 31.6% (33\104) of the total genera and species of succulents study area, followed by Aloeaceae representing by 1 genus and 8 species, Crassulaceae represented by 3 genera and 6 species, then Asteraceae. represented by 3 genera and 5 species and Lamiaceae represented by 1 genera and 5species.It was noted that the generic index was 2(52\104), that means that the study area has high diversity. These results agree with (10 ، 30).

Chorological affinities
Phyto-geography, which is known to botanists, phytogeography or plant geography, as Good (36). Its aims to record and then, if possible to explain, the distribution of plants over the world's surface (16). Early plant geographers and phytogeographers in the last century and the first half of this century have delimited the globe into natural chorological units or phytochoria according to different bases. These natural chorological units or phytochoria were delineated by some authors, such as Schouw (53), on a purely floristic classification, namely in accordance with the distribution, presence and absence of certain families, genera and species that are endemic to a particular region. Phytogeographical elements include Structure of succulent species of the study area with respect to origin "Chorophyte".The chorological studies showed that Monoregional species constitute a remarkable portion of the studied succulent flora, 77.8% (81) of species were native to the Sudano-Zambenzian phytochoria. The second dominant phytochoria was Bi-Regionalconstitute (11.46 %) "Sudano-Zambenzian + Saharo-Sindian(11 sp. 10.5%) and Sudano-Zambenzian +Mediterranian(1 sp. ., 0.96%). While Plueriregional comprise (11sp. ; 10.57 %) "TheTri-Regional element "Sud-Zam +Sah-Sin+ Med, 3 sp. Cosm. 5 sp. ; Trop. 2 sp. ; Pan. 1 sp." (Table 1; Fig. 1).The dominant Sudano-Zambenzian region confirm that the study area "as a part of Yemen" belong to the African Horn region, our results agree with (3 ، 5 ، 44 ، 37).The results proved that the Sudanian-Zambezian regions are home to the most of the succulent species. Zohary (62) and Takhtajan (57) indicated that south and south-western Arabian Peninsula is one of the richest areas of the Sudanian (Sudano-Zambezian) territories, However, this area is the richest part of the Arabian Peninsula in terms of endemic species (16).

Life forms spectrum:
According to Raunkiaer, (51) that the climate of a region is characterized by life form and the propose of life form classification system based on the manner in which plants protect their perennating buds during unfavorable seasons. Life-form is the sum of all the adaptations undergone by a plant to the climate in which it resides (41). Raunkiaer (51) proposed the term "Biological Spectrum" to express both the life-form distribution in a flora and the phytoclimate under which the prevailing life-forms evolved. Literature dealing with the life form demonstrated that a very little work has been made in Yemen. Accordingly, life form of the study area exhibit that the most frequent life form class was Chamaephytes with the maximum number of species they are represented by 46 species (44.23%), followed by Phanerophytes represented by 29 species (27.88%), Geophytes 13 species (12.5%), Hemicryptophytes 9 species (8.65%) and Therophytes are represented by 6 species (5.76 %) 1 parasite (0.96%) ( Table 2; Fig. 2).The dominance of the Chamaephytes life form may be attributed to the hot dry climate, topographic variation and biotic influence, while Phanerophytes provide good evidence that their abundance is, in fact, an expression of monsoon climate. These results agree with (12 ، 10). Same results from neighboring countries, such as Taif, Hail and Najd regions in Saudi Arabia (48 ،33) reported that the dominant life form of those regions are Therophytes and Chamaephytes. Abd-El-Ghani and Abdel-Khalik (1), from the south east Egypt, reported that the dominant life forms of that region are Chamaephytes, Therophytes and Phanerophytes.. That mean the study area has been under heavy biotic and abiotic pressure.
Endemism is a key component of biodiversity that, particularly, interests biologists and plant taxonomists (14). it's also an important concept in conservation biology and is considered one of the criteria used to set priorities for species conservation efforts. A taxon (e.g. a species) is considered endemic to a particular area if it occurs only in that area (29). One of the most distinct features of the flora of Yemen is the high percentage of the endemic plants among its components (13 ، 61 ، 15).The endemic and near endemic succulent plants in the study area represented by 39.4% (41\104) of the total collected area and constitute 27.3 % (41\150) of endemics in succulent flora of Yemen as a whole. The percentage explain the richness in species and endemics that interpret the high importance of the study area floristically.