Saxicolella nana Engl.

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 : 417-419

4. Saxicolella nana Engl. ( Engler 1926: 356 taf. XVII: 1);

Engler (1920: 38 fig 27); Onana & Cheek (2011: 253); Onana (2011: 116); Onana (2012: 137).

Type: Cameroon, Centre Province, “ In Nyong sudlich von Jaunde , Januar 1913 ” (in the Nyong Sof Yaoundé , Jan. 1913) Mildbraed 7739a (holotype B [ B100293988 ] ; isotype U [ U1518022 ] n.v.).

Annual herb (probably), c. 5 mm high. Root crustose c. 5 mm diam., margin lobed. Shoots several from the centre of the crustose root, stems c. 1.5 mm long, bearing 2 (– 3) spirally inserted leaves separated by short internodes, terminated by a single spathellum. Leaves 1.5 – 6 mm long, proximal part 1.5 – 1.6 mm terete c. 0.2 mm diam. distal (1 –) 5 mm (2 –) 2 (– 3)- fid, the divisions equal, filiform. Spathellum pedunculate, peduncle to 2 mm long; spathellum obovoidclavate, 2 – 2 × 0.9 mm, apex obtuse, opening by radial fissures, producing long triangular teeth. Flower carried c. 1 mm beyond the spathellum. Pedicel 2.5 – 2 mm long. Tepals filiform, 0.3 mm long. Stamen with filament 2 – 2 mm long. Pollen in dyads. Gynophore 0.5 mm long. Ovary fusiform, 1.5 × 0.6 mm. Stigmas linear, 0.5 mm long. Fruit ellipsoid dimensions as

ovary, 6-ribbed, dehiscing by a single suture. (Fig. 3).

RECOGNITION. Similar to Sapicolella sp. A (see below) but differing in the disc-like root, the shoots produced at its centre (not ribbon-like, the shoots at the margin), a distinct gynophore present, fruit 6-ribbed (vs ovarysessile, fruit 8-ribbed).

DISTRIBUTION. Cameroon, Centrale province. Only known from the type locality near Mbalmayo, Nyong River.

SPECIMENS EXAMINED. CAMEROON. Centre Province, “In Nyong sudlich von Jaunde, Januar 1913” (in the Nyong Sof Yaoundé, Jan. 1913) Mildbraed 7739a (holotype B [100293988]; isotype U [U1518022] n.v.); “11°27ˈN, 2°22ˈE” (likely 2°22ˈN, 11°27ˈE), 28 Feb. 2007, M. Kato, R. Imaichi, S. Koi & N. Katayama CMR-129 (YAN.v.) (cited in Kuetegue et al. (2019) see notes below).

HABITAT. Rapids in the river Nyong at Mbalmayo., in full light, in the semi-deciduous forest belt. Growing with Macropodiella heteromorpha (Baill.) C.Cusset (published as Macropodiella mildbraedii Engl. ( Engler 1920: 38)). Alt. c. 220 m.

CONSERVATION STATUS. Sapicolella nana was assessed in 2007 as VU D2 ( Ghogue 2010), citing a single location, the Nyong at Mbalmayo, with an AOO of <20 km 2 and major threats of water pollution, temperature extremes and sudden drought. Independently, a provisional assessment of CR B2ab(iii) was made in Onana & Cheek (2011: 253), unaware that at this point, Ghogue had rediscovered the species likely at the type locality in 2003, the samples all being sent to Z. Cameroon has been relatively well-surveyed for Podostemaceae thanks to pioneering collectors in the German colonial period (1883 – 1916). More recently intensive surveys dedicated to finding sites for this family in Cameroon have been carried out above all by Ghogue, but also by dedicated Podostemaceae researchers from Switzerland, Ghana, USA, Japan and Britain but no further locations for Sapicolella nana have come to light. Much of the length of the Nyong S of Yaoundé is not suitable for Podostemaceae due to the absence of rapids. However, some other rapids can be detected there on Google Earth (viewed June 2021) and would be worth visiting at the correct season to establish if the species has more than a single site. We know of no hydro-electric dams planned for the Nyong at present but this could well change given the number of dams planned elsewhere in Cameroon. We contend that the data presented merits reassessment as Critically Endangered CR B1+B2ab(i-iv).

PHENOLOGY. Flowering in January.

ETYMOLOGY. The specific epithet refers to the small stature of the species.

NOTES. The type at Bwas annotated by C. Cusset in 1973 as “ Pohliella nana (Engl.) C. Cusset ” suggesting that at that time she intended to make Sapicolella a synonym of Pohliella . She did not publish the combination and reversed the decision by the time she published her Flore du Cameroun account, when instead she sank Pohliella into Sapicolella ( Cusset 1987) .

The holotype at Bbears three separate drawings. One of these appears to be made in the field by the collector, Mildbraed and shows the thalloid crustose root with a statement that the thallus firmly adheres for its entire surface. The second sketch (reproduced here as Fig. 3) is the most comprehensive and shows numerous welldelineated thumbnail sketches of the dissected specimen some of which do not figure in the published illustrations e.g. Engler (1926), presumably due to space limitations. The third drawing is a more roughly drawn outline of parts of the second with an ink caption that may have been a guide to the journal designer in assembling the published image. The second drawing shows that both the stem and root thallus are better developed than is figured in the protologue, perhaps to save space. We credit the illustrations to Josef Pohl (for whom Pohliella was named) who provided scientific illustrations for Engler for 30 years (Anon. 2018).

The description above is based mainly on Engler (1926) and Cusset (1987).

Ghogue rediscovered Sapicolella nana in rapids in the Nyong near Mbalmayo, the presumed and likely type locality (details on the type label are indicative of this but not precise) which later in 2007 provided the source of material sequenced in phylogenies such as Koi et al. (2012). Kuetegue et al. (2019) studying the rheophytes of Cameroon did not refind this species but concluded that it should be assessed as Endangered EN B2ab (ii, iii).

When finalising this paper, recent records were found from Gabon on GBIF which are attributed to the species. However, from the images available, they seem to show several important differences from Sapicollela nana and are therefore provisionally identified in this paper as Sapicolella sp. A (see below under unplaced species). If our hypothesis is incorrect and these specimens are shown to be Sapicollela nana , the extinction risk assessment for this species is likely to be reduced from the proposed CR to EN.