Saxicolella angola 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 : 415-417

3. Saxicolella angola Cheek sp. nov.

Type: Angola, Cuanza Sul , Gango-Cuanza , Mussende , 1000 m alt., fl. fr. 21 June 1920, Gossweiler 9328 (holotype K [ K000325202 ]).

http://www.ipni.org/urn:lsid:ipni.org:names:77297283-1

Annual (probably) herb, 1.2 – 1.9 cm tall. Root incompletely seen, probably crustose. Portion at base of stem (Fig. 2A) shield-like c. 1.1 mm diam., irregularly convex. Stems unbranched, erect, stout, selfsupporting 9 – 15 mm long, terete, c. 0.5 mm wide at base, increasing to c. 1 mm diam. at apex. Proximal 1.8 – 5.5 mm lacking leaf-scars, distal portion with 5 – 7 leaf scars, internodes 0.5 mm long (proximal-most internodes) to 2 mm long (more distal internodes). Scars ± amplexicaul, distal nodes with leaf bases persistent, sheathing (Fig. 2B); stem apex with a head of flowers surrounded by clusters of heteromorphic leaves, phyllotaxy spiral. Leaves of outermost (proximal) part of apical cluster ligulate, 2.5 – 2 × 0.25 – 0.2 mm, or spatulate, that is with the distal end broader, elliptic, 0.8 × 0.3 mm, apex rounded or obtuse, base slightly sheathing, stipules absent (Fig. 2C); innermost, more distal leaves of apical cluster broadly ovate, or ovate in outline 0.6 – 1 (– 1.5) × 1 – 1.5 mm, apex entire or slightly or deeply bifid, lobes equal or unequal, base broad, with or without marginal stipules. Stipules sometimes exceeding blades, subulate 0.5 × 0.2 mm. Spathellae in terminal cluster of (2 –) 5 – 8, pre-dehiscence narrowly ellipsoid c. 2.5 × 0.8 mm, dehiscing into (2 –) 2 – 5 subequal lobes, overall c. 2.5 × 1.5 mm. Flower partly concealed in spathellum at anthesis (Fig. 2D). Pedicel 0 – 0.5 mm long, concealed in spathellum. Tepals not seen. Stamen exceeding gynoecium, filament 2 – 2.05 mm long, anthers c. 0.3 × 0.2 mm. Pollen not seen. Gynophore 0.1 – 0.2 mm long. Ovary ellipsoid 1.5 – 1.8 × 0.6 mm, in transverse section suborbicular, unilocular; longitudinal ribs 6, ribs well-defined, 0.06 – 0.07 mm wide, commissural ribs absent. Stigmas 2, united at base, erect, cylindric, 0.3 – 0.35 × 0.1 mm, apex acute. Fruit about same size as ovary, mainly contained in spathellum (Fig. 2E) dehiscing by 2 equal valves, placenta spindle-shaped, 0.1 – 0.15 mm diam. Seeds ellipsoid c. 0.25 × 0.12 mm.

RECOGNITION. Differs from other species of Sapicolella with elongated stems ( S. ijim and S. flabellata ) in that the stems are unbranched (not highly branched), stigmas shortly cylindrical (not filiform, nor complanate); spathellae narrowly ellipsoid (not obovoid nor globose); leaves a mixture of simple-ligulate and ± isodiametric entire or bifid (not, only deeply quadrid, nor only simple-ligulate).

DISTRIBUTION. Angola, Cuanza Norte and Cuanza Sul Provinces (Cuanza River and its affluents).

SPECIMENS EXAMINED. ANGOLA, Cuanza Norte, Loanda Moaba, Duque da Bragança (now Kalandula Falls), Lucuala R., 1000 m alt., “on rocks of river Loando near the waterfall”. fr. 29 Aug. 1922, Gossweiler 8858 (K000592225); Cuanza Sul, Cuene or Cuno, bridge on river, “submersiherbosa, Limno Nereida” 650 m alt., 12 July 1927, Gossweiler 11252 (COI [COI00071835]); Cuanza Norte, Cuanza R., Punta Filomeno da Camera, 100 m, submerged rocks, scarlet red plants, st. 7 March 1928, Gossweiler 12027 COI [COI00071833].

HABITAT. Waterfalls and rapids exposed to full sun, with gallery forest, 1000 – 1300 m alt. Occurring at the type locality near Mussende, with other species of Podostemaceae : Inversodicraea digitata H.E.Hess and Tristicha trifaria (Gossweiler 9291, BM, n.v., COI [COI00022957], ZT n.v.). At the Kalandula Falls, Cuanza Norte, occurring with Ledermanniella aloides (Engl.) C.Cusset (Gossweiler 8858A), Tristicha trifaria (Gossweiler 8858B) and Inversodicraea fluitans H.E.Hess (Gossweiler 8855, 8856, 8857) ( Cheek et al. 2017b: 129). At Punta Filomeno da Camera, occurring with an unidentified Podostemaceae collected later that year (25 June 1927) “in swift currents of water” (Gossweiler 10697 COI [COI00022111]).

CONSERVATION STATUS. Known from four collections, each at a different location of the Cuanza or an affluent. The collection site of “Punta Filomeno da Camera” has not been found but its altitude of 100 m on the Cuanza corresponds with the hydroelectric dam at Cambambe and so it is likely that the species has been lost at this location. However, the identification of the specimen is not completely certain since it was sterile and only viewed online. The site at “Cuene or Cuno, bridge on river”, since it is at 650 m alt. on the Cuanza, corresponds with the newly constructed Lauca Hydroelectric project, Angola’ s largest. Here again the species is unlikely to survive due to the loss of its habitat and hydrological change. This leaves two locations upstream where the species is likely to survive. These two locations are c. 200 km apart. Gossweiler 9328 (type specimen) near Mussende was recorded 21 June 1920 (presumably an error by Gossweiler for 1 July). The exact site was not given, but is most likely to be the ford across the Gango River 16.5 km from Mussende on the road to Quibala (10°26ˈ07.7" S, 15°52ˈ39. 53"E observed on Google Earth), since this set of rapids is closest to Mussende (the town and river mentioned on the label) and is most readily accessible from that town. That vehicles are likely to drive over the plants at the type locality is highly possible, and this would constitute a threat. The second locality, the Kalandula Falls (also known as the Calandula falls and formerly Duque de Bragança falls) on the Lucuala (or Licuala) River (Gossweiler 8858, 29 Aug. 1922), is now a major tourist attraction, probably because it is one of the major falls by volume in Africa and is only 260 km by road from the capital, Luanda. It is evident from the numerous posts of photographs by tourists on the internet (https://en.wikipedia.org/wiki/ Kalandula_Falls accessed 20 May 2021) that trampling by visitors occurs, which can destroy plants of Podostemaceae as at the Lobe Falls in Cameroon ( Cheek et al. 2017b). Both locations, are here ascribed an area of occupancy of 3 km 2 as preferred by IUCN (2012). Therefore, Sapicolella angola is here assessed as Endangered EN B2ab(iii) using the categories and criteria of IUCN (2012). Despite this assessment, and the fact that this species has not been recorded in the wild for 78 years, and despite the fact that Hess (1952), a Podostemaceae specialist who visited the Kalandula Falls in 1950 did not find the species there, we doubt that this species is extinct, although it is probably not common. This is because at both known locations, further apparently suitable habitat can be seen on Google Earth immediately upstream and/or downstream. However, there is no guarantee that the species occurs at these sites because it is rare and infrequent (only 2 of the 25 Angolan Podostemaceae held at COI are this taxon, and one of these is only doubtfully identified). Finally, there is no cause for complacency about the security of this species since the surviving two sites are both at risk of future new hydroelectric projects in which there is currently an upsurge in Africa and which are inimicable to the survival of Podostemaceae ( Cheek et al. 2017b) .

Angola is currently going through a surge of development posing risks to its species-diverse Flora. Additional range-restricted newly described species endemic to Angola are Justicia cubangensis I.Darbysh. & Goyder ( Darbyshire & Goyder 2019) and Stomatanthes tundavalaensis D.J.N.Hind ( Hind & Goyder 2013).

PHENOLOGY. Only collected in flower (end June) and fruit (August) at the end of the dry season, the wet season being September to April

ETYMOLOGY. Named for the country of Angola as a noun in apposition. This species is both unique to Angola and the only species of the genus currently known to occur in the country.

NOTES. Sapicolella angola was first recognised as a distinct species, but informally, and not published, by C. Cusset in 1975. This is evident from her annotations of all four specimens of the species cited in this paper. She had annotated two specimens of what appears to be this taxon (Gossweiler 11252 and Gossweiler 12027 at COI, viewed online May 2021) as “ cf. Sapicolella angolensis ” dated 1975. Two other specimens, the basis of the description above, were sent on loan from Kto Pin 1982 (registered at Kas H960/82) and were annotated as “ Sapicolella gossweileri C. Cusset ined. 1998”, on one of which she had deleted an earlier annotation she had made of “ Pohliella angolensis C.Cusset ined.”. Since the Code ( Turland et al. 2018) advocates that such names should not be perpetuated without the permission of the author, and since that permission has not been obtain- ed, an alternative name has been selected.

Sapicolella angola is incompletely known. Both collections studied comprise of fruiting material. The roots, stem leaves, flowers at anthesis, pollen, are all either unknown, or only partially known. The ecology (microhabitat-ecological niche) is also unknown. Further field studies to fill these large gaps in our knowledge are advisable.