Inversodicraea koukoutamba Cheek, 2019

Inversodicraea koukoutamba Cheek View in CoL , sp. nov. — Fig. 1 View Fig , 2 View Fig

Differs from all other species of Inversodicraea in that the 3 styles are each bifurcate at the base (flowers appearing 6-stylous); no other species has bifurcate styles, and all but two other species (see below) have 2 styles, not 3; it also differs from all other species in the massive size of the erect rubbery stems, 7 – 20( – 35) cm tall (other species of the genus have stems either horizontal, not free-standing, or if free-standing usually < 4 cm tall; if exceeding this, the stems woody 4 – 8( – 20 cm) tall). — Type: Cheek 18950 (holo K; iso HNG, P), Guinea, Guinée-Moyenne, Labé Region, Tougé Prefecture, Koukoutamba Falls , fl. 14 Jan. 2018.

Etymology. Named as a noun in apposition for the type and only known locality, the Koukoutamba falls in Tougé Prefecture, Labé Region, in the Fouta Djalon Highlands of Moyenne Guinée, Guinea.

Annual or perennial herb. Root ribbon-like 1.1 – 1.8 mm wide ( Fig. 1d View Fig ). Stem erect, free-standing, rubbery, 7 – 20( – 35) cm tall; (2 –) 4 – 10 mm diam at base when live, basal 1/2 to 1/3, unbranched, lacking scale-leaves; distal 1/2 to 2/3 with spur-branches mostly 0.4 – 1.2 cm long, internodes 0.5 – 1 cm long, spur-branches increasing in length and number of shoots with distance from point of attachment, proximal spur-branches with 1 – 2 shoots, distal-most branches with c. 30 short flowering shoots. Flowering shoots short and stout, 2.5 – 4 by 2 – 2.5 mm (excluding spathellum) densely clad in scale-leaves, with a single terminal spathellum. Leaves not seen, possibly caducous or not produced. Scale-leaves heteromorphic, stage-dependent. Scale-leaves of proximal portion of main axis covering <5 % of surface, broader than long, semi-circular 0.1 – 0.2( – 0.5) by 0.5 – 0.6 mm, entire, apex rounded, entire ( Fig. 1e View Fig ). Scale-leaves of flowering shoots stout, more or less flat, completely covering and adpressed to the stem surface, those at i) shoot base 0.5 mm long, deeply 3-lobed, broader than long, the basal,

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unbranched part 0.2 by 0.3 mm, the distal 3-lobed part with a large triangular central lobe 0.3 by 0.2 mm, the two lateral lobes 0.2 by 0.1 mm, slightly spreading; ii) mid-shoot scale-leaves c. 1.3 mm long, the basal unbranched portion 0.8 by 0.3 mm, the central lobe 0.5 by 0.15 mm, the two lateral lobes as in the shoot basal scale-leaves; iii) distal scale-leaves (subtending the spathellum) entire, unlobed, narrowly triangular 1.3 by 0.3 – 0.4 mm (i–iii) depicted left to right, with intermediates, Fig. 1h View Fig ). Spathellum shortly ellipsoid, 2 by 1.5 mm, apex with a short, broad mucro 0.2 mm long, dehiscing irregularly. Pedicel 6.5 – 7 mm long. Tepals 2, filiform, erect 0.2 mm long. Androecium with two stamens. Andropodium 1.5 mm long. Free filaments 1.5 – 1.6 mm long. Anthers 1.2 – 1.4 by 0.6 – 0.7 mm. Gynophore 0.5 – 0.6 mm long. Ovary narrowly ellipsoid 2.5 – 2.75 mm long by 0.8 – 1.05 mm, wide (non-commissural plane), laterally flattened, in the commissural plane (c. 0.6 mm wide), unilocular, longitudinal ribs 6, broad and deep, ribs each 0.2 by 0.1 mm. Stigmas 3, purple red, each bifurcate from the base, horizontal, (0.4 –) 0.5 mm long, sometimes the branches themselves bifurcate at apex, apices tapering to an acute point. Fruit and seed not known.

Distribution — Guinea, Fouta Djalon, Moyenne-Bafing, Bafing River, known only from the Koukoutamba Falls.

Ecology — Rheophyte growing on rocks in the full-force of the torrent, in full sunlight; 470 m altitude.

Conservation — Inversodicraea koukoutamba is known from a single location, the Koukoutamba Falls , at which we measured its AOO (and so also the EOO) as less than 4 km 2, using the IUCN-preferred cells of that size. Here it is threatened with extinction by the imminent placement of the Koukoutamba hydroelectric dam. Following environmental studies by Tractebel Engineering, construction by Sinohydro is due to begin in 2019 ( Pigeon 2017). The World Bank is reported to have supervised the Environmental and Social Impact Assessment (ESIA) for the project, although the outcome of these has been controversial ( Watts 2018).The construction works have been commissioned by the Organisation pour la mise en valeur du fleuve Sénégal (OMVS), led by Hamed Diane Semega who announced in April 2018 that the work would go ahead soon ( Atcha 2018). It is to be hoped that this species will be found at additional locations where it might survive, so reducing the extinction risk, but this is far from certain. Many species of Podostemaceae are known to be single-site endemics. Therefore, using the precautionary principal advocated by IUCN (2012), the species is here assessed as Critically Endangered (CR B1+B2ab(iii)) since placement of hydroelectric dams at waterfalls with endemic species of Podostemaceae has been documented to have caused local species extinctions ( Cheek et al. 2017a, Cheek 2018, Cheek & Magassouba 2018).

It is to be hoped that efforts will be made to bank the seed of this species and to make efforts to translocate it to suitable safe sites, or that other measures can be taken to protect it from extinction at Koukoutamba.

Additional specimen. Guinea, Guinée-Moyenne, Labé Region, Tougé

Prefecture, Koukoutamba Falls , fl. 13 Jan. 2018, Cheek 18943 ( HNG, K) .

Notes — Inversodicraea koukoutamba was initially identified in the field by the first author as Inversodicraea abbayesii which also occurs in the Fouta Djalon of Guinea, but in a different drainage system, an affluent of the Konkouré River. However, although the scale-leaves of the two species are similar (see Taylor 1953: 68) there are numerous points of separation (see Table 1).

Inversodicraea koukoutamba is only the third species of Inversodicraea known to have three, not two, stigmas. Those other species are:

1) Inversodicraea ntemensis (Y.Kita, Koi, Rutish. & M.Kato) J.J.Schenk, Herschlag & D.W.Thomas ; and

2) I. ebo Cheek ( Cheek et al. 2017a) .

Both are globally endemic to the Memve’ele Falls of Cameroon. However, I. koukoutamba is unique in the genus in having each of the three stigmas bifurcate. The species is also unusual in being the tallest (6 – 20( – 35 cm) free-standing member of the genus, exceeding I. cristata Engl. , I. ebo (both c. 7 – 8 cm tall) and I. tchoutoi Cheek (4( – 20) cm tall), all of which occur in Cameroon, far to the east of Guinea. Inversodicraea koukoutamba also differs from the preceding three species in the stem being rubbery and not woody.

The Koukoutamba Falls on the Bafing River of Guinea, with five species, have the highest species-diversity for Podostemaceae of all waterfalls documented to date in Guinea, and possibly in the whole of West Africa. This is exceeded in Central Africa by the Lobé Falls of Cameroon, with ten species, which holds the record for Podostemaceae species-diversity in Africa ( Cheek et al. 2017a).

The other four species of Podostemaceae present at Koukoutamba Falls are:

1) Tristicha trifaria L. (the most widespread and common Podostemaceae in Africa);

2) Stonesia taylorii C.Cusset (restricted to the Bafing River, with only three global locations, assessed as EN ( Cheek & Molmou 2018);

3) Inversodicraea harrisii (C.Cusset) Cheek restricted to Guinea and Sierra Leone and assessed as Endangered ( Cheek et al. 2017a) but which has subsequently been discovered at additional locations (Cheek pers. obs. Jan. 2018) ;

4) Lebbiea grandiflora Cheek , assessed as Critically Endangered ( Cheek & Lebbie 2018).

Each of these five species has its own niche within the falls at Koukoutamba, and usually different phenologies. In January 2018 we observed that the plants of species 1) and 3) had already long been fully exposed and were dead and dried, being c. 60 cm above the water-level at that time.

Plants of 4) occupied flat, horizontal surfaces of rock and c. 90 % of the individuals were dried and dead, with only c. 10 % still alive and flowering. Plants of 2) were attached to vertical rock steps in the falls, the long flexible stems draping down, covering the vertical surfaces, they were only c. 5 % at flowering stage, the remainder post-anthetic.

Inversodicraea koukoutamba occurred only in foaming white water in the fastest flowing and most turbulent places at the top edges of the falls, with only the apices of the stems rising above the spume. Of all the five species present, it alone had not yet reached the fruiting stage in January. It is possible that it alone at this site is perennial since it grows deeper in the water than the other species at sites which may remain wet through the dry season, while the other species seem to be annuals completely drying and so dying after fruiting.

Below the Koukoutamba Falls , a flat open apron of rock and rubble 250 m long spreads out 70 m wide on the north side of the river. In the wet season this must be covered in fast-running water since it supports a community of specialised plants, all of which seem to be rheophytic (adapted to fast-flowing water). These include unusual species of herb, including Portulaca and Pennisetum , shrubs including Zizyphus and Ormocarpum , and scattered stunted trees of Pterocarpus santalinoides . This community will be reported on in detail in a separate publication when identifications are completed.

The Bafing River at this point in its descent from the Fouta Djalon highlands, flows through open woodland with Borassus , with areas of open ferralitic bowal close by. Barleria asterotricha Benoist ( Acanthaceae ), assessed as Critically Endangered ( Rokni 2017), was the only other rare, threatened species recorded by us at the Koukoutamba Falls themselves, being localised to the denser woodland in this area. While some sec- tions of the river are lined by evergreen gallery forest some tens of metres wide, there is none at the falls themselves, but such forest begins just downstream where the river narrows and deepens to only 30 – 40 m wide, while at the falls the river spreads to 170 m wide, dropping in three shallow steps a few tens of metres apart. The total drop from the top ( 480 m above sea-level) to the bottom of the falls is about 11 m as measured on Google Earth.