Saxicolella deniseae Cheek

Cheek, Martin, Molmou, Denise, Magassouba, Sekou & Ghogue, Jean-Paul, 2022, Taxonomic revision of Saxicolella (Podostemaceae), African waterfall plants highly threatened by Hydro-Electric projects, Kew Bulletin 77 (2), pp. 403-433 : 420-421

6. Saxicolella deniseae Cheek sp. nov.

Type: Guinea, Kindia-Télimelé Rd, 5 km Sof crossing over the Konkouré R., on the Mayankouré near Lamba Sosso village , 10°23ˈ15.3"N, 12°58ˈ20.8"W, 180 m alt. fl. fr. 27 Jan. 2018, Molmou 1682, with Gbamon Konomou (holotype HNG; isotype K [ K000592221 ] ).

http://www.ipni.org/urn:lsid:ipni.org:names:77297286-1

Annual herb. Root crustose, flat, covering the substrate in irregular oblong-shapes 5 – 18 × 7 – 23 cm, the margins with numerous radiating roots, each ribbon-like, 1.5 – 3 × 0.3 cm, tapering slightly to 0.25 cm wide towards the rounded apex (Fig. 6A & B), not, or rarely, branching. Shoots sessile, short, monomorphic, at both margins of the root, rosettes (spiral phyllotaxy) of (2 –) 2 leaves with a terminal spathellum, stems separated from each other by (0.15 –) 0.18 – 0.25 (– 0.3) cm. Leaves heteromorphic, proximal leaves suborbicular 0.2 – 0.5 cm diam., concave, sheathing, sometimes with a minute apiculus 0.05 – 0.1 cm long, stipules absent; distal leaves oblongelliptic, 1.1 – 1.5 × 0.5 (– 0.7) mm, including a short linear apical blade 0.2 – 0.6 × 0.1 – 0.15 mm, apex rounded; stipules equal, flanking the linear blade, triangular, c. 0.05 mm long, rarely absent. Spathellum pre-dehiscence ellipsoid c. 1.2 × 0.75 mm, mucro indistinct; at dehiscence c. 2.2 × 0.9 mm, with irregular dehiscence flaps. Flowers single per stem, terminal, erect in spathellum. Anthetic flowers with ovary half concealed inside spathellum (Fig. 6G). Pedicel erect 0.9 – 1 mm long at anthesis (0.15 mm long in undehisced spathellum) accrescent, increasing to 1.5 mm long in fruit. (Fig. 6J). Tepals 2, filiform, erect, 0.5 mm long, apex acute. Stamen 1, filament 1.6 – 2.6 mm long, slightly or far exceeding the ovary; anther cells oblong-ellipsoid, slightly diverging from each other in direction, (neither opposite, nor parallel) 0.25 (– 0.3) mm long. Gynoecium, gynophore accrescent, 0.75 mm long in fruit. Ovary ellipsoid, at anthesis 1.2 × 0.3 mm, increasing in fruit to 2 × 0.65 mm, orbicular in transverse section, with eight more or less equal longitudinal ribs (commissural ribs well-developed). Stigmas 2 narrowly botuliform, 0.25 – 0.25 mm long, erect, minutely papillate, apices obtuseacute. Fruit with placenta spindle-like. Seeds oblongellipsoid, 0.12 × 0.05 mm.

RECOGNITION. Sapicolella deniseae is most similar morphologically to S. marginalis (G.Taylor) Cheek because both species share numerous rosulate sessile stems inserted at the margin of the ribbon-like roots. Sapicolella deniseae differs in that the three rosette leaves are shorter than the ovary; and in that they are comprised of a concave orbicular sheathing base with only a rudimentary linear apical blade, the apex rounded (in S. marginalis there are 5 – 7 rosette leaves, each narrowly triangular-subulate, the sheathing base inconspicuous, the blade apex acute); in S. deniseae the stigmas are narrowly botuliform (in S. marginalis complanate).

DISTRIBUTION. Guinée, Kindia-Télimelé, Konkouré River.

SPECIMENS EXAMINED. GUINEA. Only known from the type specimen: Kindia-Télimelé Rd, 5 km Sof crossing over the Konkouré R., on the Mayankouré near Lamba Sosso village, 10°23ˈ15.3"N, 12°58ˈ20.8"W, 180 m alt. fl. fr. 27 Jan. 2018, Molmou 1682, with Gbamon Konomou (holotype HNG; isotype K [K000592221]).

HABITAT. Rapids in river. Growing with several other Podostemaceae species, for which specimens for identification are not yet available. 173 m alt.

CONSERVATION STATUS. Currently Sapicolella deniseae is known from a single location which will be impacted by a hydro-electric project in the near future (see notes below). The area of occupation is estimated as 3 km 2 using the IUCN standard. Therefore, we here assess S. deniseae as Critically Endangered (CR B2ab(iiv)). It is to be hoped that further surveys will discover this species at other locations which are secure from threats such as hydroelectric projects otherwise this species is at high risk of extinction.

PHENOLOGY. Flowering and fruiting in January as the water level drops with the advance of the dry season. When collected in late January some plants were still emerging from the water, and live and flowering, while others had already been exposed and had concluded fruiting and died.

ETYMOLOGY. Named for Denise Molmou of Herbier National de Guinée, Université Gamal Abdel Nasser- Conakry, a leading botanist of Guinea who led the botanical survey team in which this species was discovered and who also collected the type specimen.

NOTES. Together with Sapicolella futa , this is the most westerly species of the genus. The two species are geographical outliers of the rest of the genus which is centred in the Cross-Sanaga interval of SE Nigeria and W Cameroon. Sapicolella deniseae cannot be confused with S. futa since in the first the ribbon-like roots are 0.3 cm wide, unbranched, and bear numerous sessile shoots along the root margin, while in S. futa the roots are 0.02 – 0.05 (– 0.08) cm wide and bifurcate at regular intervals, bearing single sessile shoots only at the sinus of the bifurcations.

No associated endemic plant species are recorded near the location of Sapicolella deniseae because this part of Guinea is otherwise botanically unsurveyed.

Sapicolella deniseae is known from one site on the Mayan Kouré River, an affluent that, 5 km to the north joins the Konkouré, one of Guinea’ s largest southward draining rivers. About 25 km upstream of that junction, at Donkheya, the Konkouré is dammed for a hydroelec- tric project. The reservoir extends upstream for 52 km (measured on Google Earth from imagery dated 21 Jan. 2015, downloaded 13 May 2018). This reservoir also extends up several of the affluents. About 20 km downstream of the same junction a new hydroelectric project was opened in 2017 (under construction in the Google Earth imagery of 21 Jan. 2015). The risk is that the reservoir of this project extends upstream a similar distance to that of Donkheya affecting the hydrology of its affluent, on the Mayan Kouré. Moreover, additional hydroelectric projects are planned on the Konkouré. The Konkouré river and its affluents remain almost completely unsurveyed for their plant species including Podostemaceae . Updating this before submission of this paper two years later, CNES Airbus imagery dated 11 Nov. 2018 viewed on Google Earth shows that as feared, the new reservoir on the Konkouré had already filled nearly up to the junction with its affluent, the Mayan Kouré. It is possible that by now, June 2021 the type location of Sapicolella deniseae has flooded which will have made the only known global population extinct. 1