TAXONOMIC REVISION OF SAUDI ARABIAN TETRAENA MAXIM. AND ZYGOPHYLLUM L. (ZYGOPHYLLACEAE) WITH ONE NEW VARIETY AND FOUR NEW COMBINATIONS

The genera Tetraena Maxim. and Zygophyllum L. (Zygophyllaceae) present different morphological characters, viz. growth habit, leaf features, flower traits and fruit shape, and have a high diversity of species in Africa, Australia and Asia. Six species of Tetraena [T. alba (L.f.) Beier & Thulin, T. coccinea (L) Beier & Thulin, T. decumbens (Delile) Beier & Thulin, T. hamiensis (Schwein f.) Beier & Thulin, T. propinqua (Decne.) Ghaz. & Osborne and T. simplex (L.) Beier & Thulin], and one species of Zygophyllum (Z. fabago L.) have been identified in Saudi Arabia, most of which grow in sandy soils and saline habitats as shrubs and herbs. One new endemic variety (T. alba var. arabica Alzahrani & Albokhari) along with four new combinations [T. alba var. amblyocarpa (Baker) Alzahrani & Albokhari, T. hamiensis var. qatarensis (Hadidi ex Beier & Thulin) Alzahrani & Albokhari, T. hamiensis var. mandavillei (Hadidi ex Beier & Thulin) Alzahrnai & Albokhari, and T. propinqua subsp. migahidii (Hadidi ex Beier & Thulin) Alzahrani & Albokhari] are proposed. Descriptions, illustrations, distribution maps and a key for identification of the taxa are presented. Conservation status has been proposed for the new variety and combinations.


Introduction
The genus Zygophyllum L. distributed in Saudi Arabia received much attention based on morphological and anatomical characters (Hadidi, 1978;Migahid, 1978Migahid, , 1996Hosny, 1988;Mandaville, 1990;Chaudhary, 2001;Soliman et al., 2010;Waly et al., 2011). However, according to the most recent taxonomic proposal of Tetraena Maxim. and Zygophyllum presented by Beier et al. (2003), the most Saudi Arabian taxa of Zygophyllum were transferred to Tetraena. Zygophyllum and Tetraena have similar morphological characters, viz. growth habit, leaf features, flower traits and fruit shape. Beier et al. (2003) showed that Zygophyllum and Tetraena could easily be distinguished from each other by the characters of fruit dehiscence and staminal appendages. Zygophyllum propinquum was not included in Beier et al. (2003) and it was not mentioned as a synonym under any species in their study. However, Ghazanfar and Osborne (2015) transferred this species to Tetraena propinqua.
Taxonomically, Zygophyllaceae R. Br. was placed in different orders by several authors. Engler (1964) placed the family in the order Geraniales, while Cronquist (1968) and Hutchinson (1969) positioned Zygophyllaceae in the order Sapindales. Dahlgren (1980) deposited it in the order Geraniales, following Engler (1964), but Takhtajan (1980) positioned the family within Rutales. Currently, APG III (2009) placed Zygophyllaceae with Krameriaceae within a new order 1 Zygophyllales. These two families are placed with strong support as sister to a clade containing more than two orders. Sheahan and Chase (2000) analysed both rbcL and trnL-F sequences from 36 taxa of Zygophyllaceae and their results were supported by previous classification of Zygophyllaceae into the five subfamilies (Zygophylloideae, Larreoideae, Seetzenioideae, Tribuloideae and Morkillioideae). Moreover, Sheahan and Chase (2000) have indicated that Tetraena is nested within the large and variable Zygophyllum.
The genus Zygophyllum was first described by Linnaeus (1753) and has been accepted by several authors who worked broadly on systematics of this genus (Zumbruch, 1931;Van Huyssteen, 1937;Oltmann, 1971;Hadidi, 1978;Chase, 1996, 2000;Van Zyl, 2000). Linnaeus (l.c.) classified six species within Zygophyllum, namely Z. fabago L., Z. morgsana L., Z. sessilifolium L., Z. fulvum L., Z. coccineum L. and Z. spinosum L. Based on growth habit, androecium characters and dehiscence of the capsule Van Huyssteen (1937) split Zygophyllum into two subgenera, viz. Zygophyllotypus Huysst. (= subgenus Zygophyllum) and Agrophyllum, and further subdivided Zygophyllotypus into eight sections and Agrophyllum into five sections. In this classification, Zygophyllum coccineum, Z. album and Z. aegyptium were placed in section Mediterranea Engl., and Z. simplex and Z. decumbens in section Bipartita Huysst. Z. dumosum was placed in section Alata Huysst (Van Huyssteen, 1937). Hadidi (1977) recognized eight species of Zygophyllum in Arabia and all of them belong to section Mediterranea, including two new species, i.e. Zygophyllum mandavillei Hadidi, and Z. migahidii Hadidi. Z. migahidii is closely related to Z. propinquum, but they differ in flower and fruit characters. In Z. migahidii, the flowers and fruit are solitary at each node, while they are grouped in clusters in Z. propinquum, conversely, Z. mandavillei can be easily recognized from other species of its section by its glabrous, large long-stalked flowers and sausage-shaped capsule. Later, Hadidi (1978) described Z. qatarense from Qatar as a new species. Hosny (1988) reported 13 species and three varieties of Zygophyllum in Arabia and among them10 species and one variety were distributed in Saudi Arabia. She classified them into two subgenera Zygophyllum and Agrophyllum (Necker) Endl. ex Van Huyssteen following Engler (1931) and Van Huyssteen (1937). According to Van Huyssteen (1937), two of the Saudi species belong to section Bipartita, seven species belong to section Mediterranea, including Z. boulosii A. Hosny as a new species, and two species belong to section Hamiensia Engl. Sheahan and Chase (1996) studied the phylogenetic relationships of Zygophyllaceae based on morphology, anatomy and the rbcL sequence and found Fagonia as sister to the rest of the subfamily, while Zygophyllum fabago (type species of Zygophyllum) is a sister to genus Augea, and Z. simplex is a sister to genus Tetraena and concluded that Z. simplex might not belong to Zygophyllum. Later, Sheahan and Chase (2000) investigated the phylogenetic relationships of 36 taxa of Zygophyllaceae including 15 species of Zygophyllum from Africa, Australia and southwest Asia using nucleotide sequences of the plastid gene rbcL and non-coding trnL-F. Their results agreed with a high support to the previous results that stated Zygophyllaceae needs to be divided into five subfamilies and the subfamily Zygophylloideae was further classified into five clades with a high support of bootstrap. Also, they concluded that Zygophyllum is polyphyletic. Zygophyllum fabago was nested with another Asian species, Z. xanthoxylum, whereas Z. simplex was placed in a strong clade with genus Tetraena and other species of Zygophyllum: Z. cylindrifolium, Z. decumbens, Z. album and Z. coccineum (last three are distributed in Saudi Arabia). Moreover, molecular studies have indicated that Tetraena is nested within the large and paraphyletic Zygophyllum (Sheahan and Chase, 2000).
Van Zyl (2000) made a revision for 54 species of south African Zygophyllum and classified these species into two subgenera Zygophyllum and Agrophyllum, based on morphological characters, more particularly capsule dehiscence, seed attachment and presence of spiral threads in the seed mucilage. The result agreed with classification provided by Endlicher (1841) and Van Huyssteen (1937). Takhtajan (1987) separated the genus Tetraena from subfamily Zygophylloideae and erected Tetraenoideae based on morphology of pistil, fruit, pollen grains and chromosomes. Species within the genus Tetraena can be distinguished by growth habit, plant colour, leaf structure, flower colour, and fruit type and shape (Van Huyssteen, 1937;Hosny, 1988;Van Zyl, 2000;Chaudhary, 2001;Beier et al., 2003).
Based on trnL plastid DNA sequences and morphological characters Beier et al. (2003) showed that Zygophylloideae is monophyletic, whereas the genus Zygophyllum is paraphyletic, since it was placed with the genera of Augea Thunb., Tetraena and Fagonia L. In addition, they proposed a new classification for Tetraena and Zygophyllum which is supported by combination of morphological and molecular data, transferring 35 species from Zygophyllum to Tetraena as new combinations. These species are known from Africa and Asia. Zygophyllum is characterized by a loculicidal capsule and undivided staminal appendages, while Tetraena is distinguished by a schizocarp and sometimes bipartite staminal appendages. Subsequently, many authors agreed with this transfer and used the combinations proposed by Beier et al. (2003) as valid in their works (Norton et al., 2009;Louhaichi et al., 2011;Mosti et al., 2012;Sakkir et al., 2012;Azevedo, 2014;Symanczik et al., 2014).

Materials and Methods
The present revisionary study of Tetraena Maxim. and Zygophyllum L. in Saudi Arabia is based on extensive field survey, literature and analysis of more than 348 specimens, including types and images of types from different herbaria, viz. BM, CAI, CAIM, E, K, KAUH, KSU and RIY. Field surveys were carried out in c. 31 localities, between 2013 and 2014, and 72 collected samples were deposited in KAUH (King Abdulaziz University Herbarium, Jeddah, Saudi Arabia). The collected specimens were critically studied and examined, and identifications were confirmed using standard literature (Hosny, 1988;Chaudhary, 2001;Beier et al., 2003). In each case, several duplicate voucher specimens were made and these were complemented with fresh material preserved in 70% ethanol and stored for further research.
A total of 74 morphological traits were found effective to determinate species and new combinations from field collections and herbarium specimens. These characters, including both vegetative and reproductive features, were examined and scored using a Novex dissecting microscope and X10 hand lens. Differences between species, subspecies and varieties were supported by distribution maps, diagnostic traits placed in the identification key, and drawings, and evaluation of synonyms. The conservation status for the new variety and combinations was assessed following the guidelines of IUCN (IUCN, 2014).

Results and Discussion
Zygophyllum is represented by only one species in Saudi Arabia, Z. fabago. It clearly differs from Tetraena species by several morphological characters such as size, shape and colour of leaves, flowers and fruits. The present study reveals that Z. fabago is characterized by 2-foliolate, flat leaves, up to 4 cm long, and 2.5 cm wide, creamy flowers, and loculicidal, oblong-cylindrical capsule, up to 3 cm long. This is congruent with Beier's results (Beier et al., 2003).
Habitat: Found in coastal and inland saline sandy soils, and salt marshy areas. Etymology: The varietal epithet is derived from Arabia, the area of its distribution. Conservation status: Based on its known distribution (area of occupancy estimated to be less than 10 km 2 ) and abundance (number of mature individuals less than 50), the IUCN Red List Category (IUCN, 2014) "Critically Endangered" is here attributed to this variety. Phenology: February to June. Vernacular names: Rotreyt, Qarmal, Harm. Distribution: Saudi Arabia: Shuaibah (Fig. 3). Worldwide: South Arabia (Yemen), tropical East and North Africa (Egypt).
Habitat: Salt marshy areas. Conservation status: Least Concern (lc), locally common on the west coast of Saudi Arabia, cost of Yemen, Egypt and Somalia.   (Fig. 4). Diagnosis: T. coccinea with a shrubby habit can be recognized by its cylindrical fruits and persistent triangular stipules.
Habitat: In sandy and saline soils.
Habitat: Grows in sandy soils.