Two new species of Commicarpus (Nyctaginaceae) from the Horn of Africa

The new species Commicarpus altus Thulin from central Somalia and C. ogadenensis Thulin from southeastern Ethiopia are described, illustrated and mapped. Both species are shrubs with succulent leaves and white flowers, and they have previously been treated as forms of the widespread and variable C. plumbagineus (Cav.) Standl. Commicarpus altus is found on gypseous or saline ground at elevations of 125–150 m a.s.l., whereas C. ogadenensis seems to be entirely confined to gypsum at 350–550 m a.s.l. Commicarpus altus differs from C. plumbagineus , apart from being a shrub with succulent leaves, by having a glabrous perianth and a joint on the pedicel well below the anthocarp. Commicarpus ogadenensis differs from both C. plumbagineus and C. altus by having five (versus three) stamens.


Introduction
recognized 12 species of Commicarpus Standl. in the account of the genus in Flora of Somalia, four of which had been described a few years earlier (Thulin 1990). One plant, a slender shrub growing up to at least 4 m high on gypseous or saline ground in central Somalia, caused problems. It was first thought to be a new species, but as it agreed with C. plumbagineus (Cav.) Standl. in having white flowers with a prominent perianth-tube and three stamens, it was finally regarded as a shrubby form of this very widespread and variable species. This taxonomy has now been reconsidered, and the plant in central Somalia is described below as C. altus. Gilbert (2000) treated nine species of Commicarpus in his account for Flora of Ethiopia and Eritrea, all of them also occurring in Somalia. Friis et al. (2016) described two new species from gypsum outcrops in eastern Ethiopia, one of them being an up to 3.5 m tall shrub, and provided an overview of the 14 species then known from Somalia, Ethiopia and Eritrea.
However, during field work in Ogaden in southeastern Ethiopia in 2006 and 2007, another shrubby gypsum plant had been collected in two localities by the present author, along with Hassan Yusuf Kaariye and Friedrich Wilhelmi. This again agreed with Commicarpus plumbagineus by having white flowers with a prominent perianthtube and was provisionally identified as another shrubby form of this species. As the Two new species of Commicarpus (Nyctaginaceae) from the Horn of Africa

Mats Thulin
M. Systematic Biology,Dept of Organismal Biology,EBC,Uppsala Univ.,Uppsala,Sweden. Research 2 material was poor and scanty, it was left without further study. However, Hassan Yusuf Kaariye has recently been back to one of the localities and managed to take good photographs of the plant. This stimulated a new study of the available material and this Ethiopian species is described below as C. ogadenensis.
The Horn of Africa region in the sense of Thulin (2004), now with about 20 species of Commicarpus recorded, is clearly a center of endemism and diversity for the genus. Gypsophily or gypsum-tolerance is common among xerophytic members of Nyctaginaceae (Douglas and Manos 2007), and Commicarpus ogadenensis, and to some extent C. altus, add to the list. Other examples of gypsophilous species of Commicarpus in the Horn of Africa region are C. macrothamnus Friis & O.Weber in Ethiopia (Friis et al. 2016) and C. reniformis (Chiov.) Cufod. in Somalia and Yemen. The single African member of the otherwise North American genus Acleisanthes A.Gray, A. somalensis (Chiov.) R.A.Levin (syn. Selinocarpus somalensis Chiov.), is a gypsum endemic in Somalia (Thulin 1993(Thulin , 2006. Commicarpus altus Thulin sp. nov. (Fig. 1, 2) This species differs from C. plumbagineus (Cav.) Standl. by being a slender shrub (versus herb or subshrub, woody towards base only) with succulent (versus herbaceous) leaves, glabrous (versus sparsely to densely pubescent) perianth and pedicels with a joint 1-2 mm below the base of the anthocarp (versus with joint at base of anthocarp).

Distribution and habitat
Commicarpus altus is known from the Galguduud, Hiiraan and Shabeellaha Dhexe Regions in central Somalia (Fig. 3), where it occurs on gypseous and/or saline soils at elevations of 125-150 m a.s.l. The type locality in Galguduud Region is a gypseous plain with saline depressions, where the sparse vegetation includes scattered bushes or small trees of species of Commiphora, Terminalia, Senegalia and Vachellia. The field layer includes, for example, Chascanum elburense Thulin (2005), Indigofera gypsacea Thulin (1992) and Xylocalyx carterae Thulin (1987), all with more or less narrow distributions and, to various degrees, confined to gypseous ground. According to Merla et al. (1979), the locality is within the area of the 'Taleh Evaporite', a geological formation mainly composed of anhydrite and dating from the early Tertiary. However, Abbate et al. (1994) restricted the Taleh Evaporites to northern Somalia, whereas the type locality of Commicarpus altus falls within the area of the 'Mudug Beds' with gypsiferous sands and sandy clays, dating from Oligocene to early Miocene.
The two adjacent localities in Hiiraan and Shabeellaha Dhexe Regions are on silt plains, outside the gypsiferous areas, with Limonium, Suaeda and small bush clumps and open patches of woodland with mainly Euphorbia robecchii and Vachellia reficiens. The presence of species of Limonium and Suaeda indicates saline conditions. The two localities fall within the area of alluvial deposits from the Wabi Shabeelle River, dating from Pleistocene to present (Merla et al. 1979, Abbate et al. 1994.

Similar species
In the label information of the type collection, the plant is described as a slender scandent shrub, up to at least 4 m tall, growing in bushes, whereas the paratypes Kuchar 17238 and 17394 are described as, respectively, a brittle shrub to 3 m and a shrub to 2 m. This makes Commicarpus altus one of the tallest species in the genus (hence the specific epithet), and perhaps the tallest woody one. The much more robust C. macrothamnus in the Oromia Regional State of Ethiopia is a free-standing shrub up to about 3.5 m tall with purplish pink flowers (Friis et al. 2016). Another more or less woody species growing in central Somalia is C. hiranensis Thulin, a species that can become an up to 2 m tall straggling shrub (fide Kuchar 15982), but with pink or red flowers.
However, the species that is most similar to Commicarpus altus is C. plumbagineus, the only other species in the Horn of Africa region with white flowers with a prominent perianth-tube. Commicarpus plumbagineus is very widespread, ranging in Africa from Senegal in the west to Somalia in the east and South Africa and Madagascar in the south, and is also found in Jordan, Israel, Saudi Arabia, Yemen and southern Spain (Whitehouse 1996). Commicarpus altus differs from this species by being a slender shrub (versus scrambling herb or subshrub, woody towards base only) with succulent (versus herbaceous) leaves, flowers in umbels (versus in inflorescences often composed of both umbels and verticels), glabrous (versus sparsely to densely pubescent) perianth, and by having pedicels with a joint 1-2 mm below the base of the anthocarp (versus with a joint at base of anthocarp). The position of the joint on the pedicel clearly below the anthocarp (Fig. 2) is a difference not only from C. plumbagineus, but apparently from most other species in the genus.

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The species differs from Commicarpus plumbagineus (Cav.) Standl. by being an erect and free-standing shrub (versus scrambling herb or subshrub, woody towards base only), with succulent (versus herbaceous) leaves, densely glandular pubescent (versus glabrous to pubescent) inflorescences and anthocarps, and by having five (versus three) stamens. From C. altus Thulin it differs by the densely glandular pubescent (versus glabrous) inflorescences and anthocarps, the five (versus three) stamens, and by having pedicels with a joint immediately below the anthocarp (not with joint 1-2 mm below the base of the anthocarp).

Distribution and habitat
Commicarpus ogadenensis is known from two localities in southeastern Ethiopia (Ogaden) (Fig. 3), where the species occurs in open Senegalia-Vachellia-Commiphora bushland on gypsum. The type locality near Kebri Dehar is on a gypsum plain at an elevation of 550 m a.s.l. (Fig. 4) in an area called Ceelxaar (Hassan Y. Kaariye, pers. comm.), which is also the type locality for Ceropegia gypsophila Thulin (2009b). Other more or less local gypsum endemics found there are Kleinia gypsophila Lebrun and Stork (1990) and Euphorbia suborbicularis Thulin (2009a), the latter a photographic record by Hassan Y. Kaariye.
The second locality is an area of gypsum hills, about 120 km SW of the type locality, at an elevation of 350 m a.s.l. In geological terms, both localities are within the 'Main Gypsum Formation' of Merla et al. (1979), dating from the late Jurassic to early Cretaceous. More localities of the species are to be expected among the numerous gypsum outcrops found in the region. In the geological map presented by Mengesha et al. (1996), the Main Gypsum Formation has a somewhat different extent compared to Merla et al. (1979), and the gypsum outcrops E of Kebri Dehar are not indicated.

Similar species
The material available of Commicarpus ogadenensis is poor and was provisionally identified as a form of C. plumbagineus, with which it agrees by having white flowers with a distinct perianth-tube (Fig. 4, 5B). However, the new species differs from C. plumbagineus by being an erect and free-standing shrub (versus scrambling herb or subshrub, woody towards base only), with succulent (versus herbaceous) leaves, densely glandular pubescent (versus glabrous to pubescent) inflorescences and anthocarps (Fig. 6), flowers in umbels (versus in inflorescences often composed of both umbels and verticels), and by having five (versus three) stamens (Fig. 4B). Among the species in the Horn of Africa region, the only other species that may have five stamens is C. pedunculosus (A.Rich.) Cufod., a species with bright pink or magenta flowers in head-like inflorescences. Further south in Africa, there are also, for example, C. pentandrus (Burch.) Heimerl and C. greenwayi Meikle, which may have five stamens, but both have pink to purple flowers (Whitehouse 1996).
Commicarpus ogadenensis differs from C. altus by its densely glandular pubescent (versus glabrous) inflorescences and anthocarps (Fig. 6), the five (versus three) stamens (Fig. 4B), and by having pedicels with a joint immediately below the anthocarp (not with joint 1-2 mm below the base of the anthocarp).

Additional specimens examined (paratypes)
Ethiopia, Somali National Regional State (