Commicarpus macrothamnus Friis & O.Weber

Friis, I., Gilbert, M.G., Weber, O., Demissew, S. 2016. Two distinctive new species of Commicarpus (Nyctaginaceae) from gypsum outcrops in eastern Ethiopia. Kew Bulletin 71: 34. DOI 10.1007/S12225-016-9648-3.

Type

Type: Ethiopia, Oromia Regional State, Bale Zone, Raytu Woreda, Lele Hills, lowermost part of NE slope, 127 km E of Ginir along the road from Ginir to Imi, 6°35.28'N, 41°33.62'E, 750 m a.s.l., 13 Nov. 2014, I. Friis, Sebsebe Demissew, Wege Abebe, Abubaker Adem & Ermias Getachew 15492 (holotype ETH!; isotypes C!, K! [K000569011]).

Morphology General Habit

Shrub, free standing, up to c. 3.5 m tall

Morphology Stem

Old woody stems forming a trunk up to 12 cm in diam-at the base of plant (Fig. 3C – D), growth often irregularly twisted and lateral stems may be supported by other woody plants, but main stems almost always upright

Morphology General Wood

Wood pale, with clearly marked growth rings (Fig. 3D)

Morphology General Bark

Bark on old stems greyish brown

Morphology Branches

Persistent main branches initially terete, 3 – 4 mm in diam., internodes 5 – 8 cm long, nodes sometimes slightly swollen, marked with a faint line between the opposite leaf-bases, bark pale grey to whitish grey, on stems of second growth-season finely puberulous with 0.1 – 0.3 mm long hairs that are tipped with minute colourless glandular heads Most lateral branches deciduous

Morphology Leaves

Leaves strictly opposite: petiole 1.0 – 3.5 cm long, canaliculate, slightly puberulous along the edges; lamina slightly glaucous to pale green, broadly ovate to orbicular or obovate, undulate, 4.0 – 6.5 × 2.5 – 6.5 cm, base cuneate to rounded, truncate or subcordate, margin slightly thickened, pale whitish green, usually straight, rarely faintly sinuate, apex rounded, bluntly acute or acuminate, glabrous on both sides, veins 3 – 6 (– 7) on either side of midvein, not prominent and becoming obscure towards the tip of lamina

Morphology Reproductive morphology Inflorescences

Inflorescences terminal on latest season's growth (Fig. 2B – C, 3A – B), deciduous after fruiting, up to 15 (– 20) cm long and 10 cm wide, paniculate with the ultimate branches verticels of dichasia; main peduncle 3.0 – 6.0 cm long, lowermost rachis-internode 2.0 – 4.0 cm, green, usually flushed slightly purplish pink, upper internodes pink, all parts, including main peduncle, densely beset with c. 1 mm long purplish pink sticky glandular hairs; ultimate units of inflorescences 3-flowered dichasia (occasionally reduced to monochasia, rarely to single flowers) on 10 – 16 mm long dichasial peduncles; pedicels 8 – 17 mm long, slightly elongating up to 20 mm in fruit (Fig. 2C, 3A – B, 4B)

Morphology Reproductive morphology Inflorescences Bracts

Bracts linear to lanceolate, 4 – 5 (– 6) mm long, shortly glandular pilose, caducous

Morphology Reproductive morphology Flowers

Flower buds clavate, dark green and densely glandular pubescent

Morphology Reproductive morphology Flowers Perianth

Perianth (including anthocarp) (15 –) 18 – 20 (– 24) mm long; tube 8 – 10 mm long, tinged purplish pink and with numerous purplish pink glandular hairs slightly shorter than elsewhere; limb shallowly 5-lobed, 6 – 8 mm in diam., 4 mm long; lobes rounded, slightly retuse, white or very pale pink, veins minutely pubescent (Fig. 4E)

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens 3, gently curved to almost straight, exserted by 10 – 15 mm; filaments brownish purple, glabrous, at base fused into a 0.8 – 1 mm long tube surrounding the stipe of the ovary; anthers suborbicular in outline, c. 0.5 × 0.8 mm

Morphology Reproductive morphology Flowers Pollen

Pollen globular or sphaeroidal, c. 100 μm in diam-(unacetolysed), pantoporate, spinules of exine not or hardly visible in unacetolysed pollen

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary at anthesis 0.8 – 1 × c. 0.5 mm, on 0.8 – 1 mm long stipe (Fig. 4F)

Morphology Reproductive morphology Flowers Gynoecium Style

Style slightly longer than the stamens, exserted by 14 – 17 mm, glabrous

Morphology Reproductive morphology Flowers Gynoecium Stigma

Stigma globular, c. 0.3 mm in diam-Open flowers fragrant

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

No remains of filaments or the staminal tube were observed in the anthocarp

Morphology Reproductive morphology Fruits

Fruit a single-seeded achene, c. 6 × 2.2 mm, on c. 1 mm long stipe, with smooth membranous pericarp, almost filling the inside breadth of the anthocarp (Fig. 4H) Anthocarp cylindrical to slightly clavate, slightly narrowing at both ends, finely 10-ribbed, 8 – 11 × 2.3 – 3.0 mm, most glandular hairs fall off during ripening, while 2 – 4 (– 6) irregularly scattered semi-sessile laterally compressed dark red glands develop along each rib (Fig. 3E – F, 4G)

Morphology Reproductive morphology Seeds

Seed with dark brown to almost black membranous testa, filling the pericarp completely

Morphology Reproductive morphology Seeds Embryo

Embryo c. 5 × 2 mm, horseshoe-shaped, epidermis dark grey or almost black, with cotyledons partly enveloping the hypocotyl and radicule (Fig. 4J – K)

Morphology Reproductive morphology Flowers Gynoecium Ovary Ovules

Perisperm white, at first ample, then gradually absorbed during ripening of the seed

Distribution

Africa: Ethiopia.

Commicarpus macrothamnus has been observed north and south of the road between Ginir and Imi (herbarium specimens and sight records by Friis, Weber and Sebsebe Demissew). It appears to be restricted to the hills with gypsum at Lele in Raytu Woreda, Bale Zone, Oromia Regional State; the locality is in the BA floristic region of the Flora of Ethiopia and Eritrea.

After the initial observations by Friis and Weber in 2013 we assumed that C. macrothamnus could possibly occur on other mountains with gypsum deposits at suitable altitudes, and we have therefore modelled the potential distribution of the species with MaxEnt 3.3 (Phillips et al. 2006), using four runs with eight positive presence points and 1000 absence points. For this we used an environmental dataset developed by Paulo van Breugel for modelling Ethiopian vegetation. It was not possible to produce a model based on the occurrence of outcrops of gypsaceous rocks because the two geological maps available to us, Kazmin (1973) and Yonas Mulugeta (2010 [2012]), indicated very different extents of deposits with gypsum, with the former emphasising outcrops of gypsum and the latter including the presence of gypsum also in lower strata. However, Paulo van Breugel’s environmental dataset included the 19 standard bioclimatic data layers from Worldclim (Hijmans et al. 2005), altitude from the digital elevation model by CGIAR-CSI (2008), added because it refines the rather crude extrapolated temperature variable from Worldclim, and the first 10 principle components from a Principle Component Analysis made of the 42 edaphic layers (7 variables × 6 depths) of the SoilGrids 1 km dataset (ISRIC 2013). We must assume that the SoilGrids 1 km dataset to some extent compensated for the lack of a GIS layer indicating the presence of gypsum, since the soil chemistry recorded in the SoilGrids 1 km dataset is influenced by the underlying substrate, from which the soil is partly derived.

According to this model the main potential distribution area is located along the Audo Range, whilst smaller potential areas with much lower suitability are sparsely distributed to the SW in association with unnamed mountain ranges between the Genale and the Weyb rivers and the mountains to the NE on either side of the Wabe Shebelle River north of Imi.

Ecology

Acacia-Commiphora bushland on grey soil derived from and at lowermost altitudes washed down from rocks with gypsum. Commiphora guidottii Chiov. dominant in the tree-stratum. Hardly any ground cover. 750 – 900 m a.s.l. See also the section ‘The collecting locality’. Fig. 1A – E.

Conservation

In spite of the intensive search during our field work in 2014 it cannot completely be ruled out that Commicarpus macrothamnus has a wider range associated with other outcrops of gypsum and within the area with localities with a suitability higher than 0.5, but that does not seem likely.

Locally abundant (some 500 – 1000 individuals seen along the c. 17 km stretch of road through the area with gypsum outcrops). Some plants were mature with thick trunk and up to 3.5 m high, others were young. Although no new seedlings were observed we must assume that there is reproduction. The observed population (see Table 1) has an Extent of Occurrence (EOO) of 7.3 km2 with an Area of Occupancy (AOO) of 16 km2 (cell size 2 km2). The EOO and AOO were calculated using the GeoCAT tool (Bachman et al. 2011). Under criterion B the EOO is far below the threshold of Critically Endangered (CR), and the AOO is far below the threshold of Endangered (EN). It is likely that Commicarpus macrothamnus has a wider range in the Lele Hills, possibly throughout the hills (Fig. 1A) If the peripheral points of the hills are included with the observed occurrences (see estimated records in Table 1) then the EOO increases to c. 30 km2, still below the thresholds of CR. A recent threat to the habitat at the Lele Hills has been the construction of the new road between Ginir and Imi, which might facilitate settlement, but currently, the area is sparsely populated and only occasionally visited by herdsmen.

On the hydrogeological map of Yonas Mulugeta (2010 [2012]) the area of and around the Lele Hills is indicated as 'Formation with essentially no ground water resources.' Lack of ground water makes it difficult or impossible to drill wells for increased grazing, but reservoirs for gathering rain water were being established at the new village called Beredimtu and in uninhabited areas E of the Lele Hills, creating the possibility for more intense grazing and possibly human settlements. Given the restricted known distribution and the low level of ongoing threats, Commicarpus macrothamnus should be regarded as Vulnerable (VU) according to criterion D2 (IUCN 2012). CR or EN according to criteria B1 ab (i – v) or B2 ab (i – v) are unlikely to be justified given the lack of ongoing threats to the habitats at the Lele Hills.

Note

Flowering Nov. – Dec. Fruits observed in one specimen in late Nov. at 750 m a.s.l. after an unusually wet and long rainy season.

The specific epithet is a Latinised substantive derived from Greek: μακρo- (macro) = big, large, and θάμνoς (thamnos) = shrub.

Commicarpus macrothamnus is exceptional among species of Commicarpus in its habit as an erect shrub, almost a small tree, to 3½ m high, its up to 12 cm thick and erect woody trunk, and its long purplish pink glandular hairs on the inflorescence-axes, pedicels and lower part of perianth with most flowers in distinct dichasia (Fig. 2C, 3B – D, 4B & D – F). The complex thyrsiform inflorescence-structure of C. macrothamnus is most similar to the structure in C. leleensis Friis & Sebsebe. The anthocarps of C. macrothamnus are superficially similar to those of C. hieranensis Thulin, but the anthocarps of that species are only 7 – 8 mm long, not 8 – 10 mm long as in C. macrothamnus, and have two kinds of glands: large dark sessile glands in 1 – 3 subapical whorls and smaller irregularly scattered paler glands along the ribs, not, as in C. macrothamnus, variable glands irregularly scattered along the ribs.

Commicarpus macrothamnus is a tall shrub or a small tree with thick woody stems developed during continued secondary growth with well-developed growth-rings. The habit, discussed in the section 'Habit, inflorescence organisation and terminology', is so unusual that we at first doubted that the species should be placed in that genus. Meikle (1978), after having revised the entire genus as known then, pointed out that Commicarpus is readily recognisable by anthocarps studded with large, viscid, sessile or stipitate glands and that this striking diagnostic feature was the reason for the generic name (Greek κόμμι (‘commi’): gum, and καρπός (‘carpos’): fruit). Viscid, sessile glands also develop in Commicarpus macrothamnus, although irregularly and quite late in the development of the anthocarp.

Vernacular

KONTOM, name given independently by two older and one young Oromiffa-speaking informant through the intermediary of our guide Abubaker Atem. One very young Oromiffa-speaking informant called the plant GUBI. Two independent Somali-speaking informants did not recognise the plant and had no name for it.

Use

According to the Oromiffa-speaking informants the plant is eaten by all animals grazed in the area, camels, cows, goats and sheep. One informant claimed that cows should not eat it, as they might develop stomach trouble.