Inversodicraea thollonii (Baill.) Cheek (Cheek and Haba 2016: 55)

Bidault, Ehoarn, Boupoya, Archange, Ikabanga, Davy U., Nguimbit, Igor, Texier, Nicolas, Rutishauser, Rolf, Mesterhazy, Attila & Stevart, Tariq, 2023, Novitates Gabonenses 93: a fresh look at Podostemaceae in Gabon following recent inventories, with a new combination for Ledermanniella nicolasii, Plant Ecology and Evolution 156 (1), pp. 59-84 : 59

Inversodicraea thollonii (Baill.) Cheek (Cheek and Haba 2016: 55)

Figs 4C , 6A, B

Podostemum thollonii Baill. ( Baillon 1890: 877)

Ledermanniella thollonii (Baill.) C.Cusset ( Cusset 1983: 388)

Type.

GABON • Lopé rapids in the Ogooué [ “Ogooué, rapides de Lopé”]; Jul. 1887; [0°05 ’38” S, 11°35 ’24” E]; 115 m; fl., fr.; Thollon 825; holotype: P [P00179381]; isotype: BM [BM000910405] .

Distribution.

Endemic to the Ogooué river and its tributaries, in Gabon. Before 2007, this species was only known from two collections, one from the Booué rapids on the Ogooué (N. Hallé 202b, collected in 1966) and one from the rapids of the Ogooué at Lopé (Thollon 825, collected in 1887). In 2007, three sterile collections were made in the Lenké (or Langke) river near Booué (Kato et al. GB11, GB12, and GB13, as mentioned in Koi et al. 2012) that were not identified as I. thollonii until this study. Since 2019, it has been collected 35 times in the Ogooué, and in various tributaries: the Lopé, Létili, Okano, Bissoubilam, Offooué, and Lenké rivers. All of these collections were made less than 2 km upstream from the confluence with the Ogooué river, except for the collection from the Bissoubilam river (ca 6 km away). Most (38 of the 40) of the collections were made in or along a ca 130 km long portion of the Ogooué between Alembé and Makokou in central Gabon, with the exception of two collections made in the Létili river at the border between Gabon and the Republic of the Congo. Those collections are separated from the easternmost others by ca 300 km, and it is expected that I. thollonii is also present in between.

Habitat and ecology.

Rapids in rivers from ca 20 to 600 m wide, 45-500 m in elevation. It appears to be abundant where encountered. Flowers and fruits were collected in July, August, and September. It was collected with or near to Ledermanniella aloides , L. pusilla , Macropodiella hallaei , and Tristicha trifaria . Collections made from small Ogooué tributaries ( Lopé, Bissoubilam, and Lenké rivers), larger tributaries (Okano, Létili, and Offooué rivers) as well as the Ogooué river itself revealed important ecological tolerance, previously unsuspected for this species. It has been noticed in strong as well as slow currents. It has surprisingly not been found on the Ivindo river, even at the Touné falls, close to its confluence with the Ogooué. However, only one day was dedicated to the exploration of this site, and this species may have been overlooked.

Notes.

As for other species in this study, the newly collected material revealed great morphological variability. Inversodicraea thollonii is among the Podostemaceae species showing both stemmed and stemless shoots, whereas it was originally described as having short stems 1-2 cm long ( Cheek et al. 2017). If both forms were usually collected separately, a few recent collections showed stemmed and stemless shoots on single individuals (Boupoya 1948 and 1968, for instance). Stem-scales also show variability, most of them being narrowly triangular with rounded apex as described by Cusset (1983), but in some cases almost linear (Boupoya 2452). Stem-scales are usually spreading and quite delicate (thin). On stemmed individuals, stem-scales are scarce, as described by Cusset (1983), and never covering more than 50% of the stem as the key to all species provided in Cheek et al. (2017) mentions. On stemless individuals, stem-scales are forming a dense crown below the spathellae. With 40 collections to date, I. thollonii is now considered as one of the most common Podostemaceae species in Gabon, even though it is yet to be found in other watersheds than that of the Ogooué river.

Figures

Figure 4. Distribution maps of Podostemaceae in Gabon. A. Inversodicraea annithomae (grey circles), I. boumiensis (red diamonds). B. Inversodicraea nicolasii (red diamonds), I. paulsitae (grey circles), I. tenax (orange triangles). C. Inversodicraea thollonii (red diamonds), Ledermanniella bifurcata (grey circles). D. Ledermanniella aloides (grey circles), L. schlechteri (red diamonds).

Figure 6. Photographs illustrating a selection of species treated in this paper. A, B. Inversodicraea thollonii (A: Boupoya et al. 1948; B: Boupoya et al. 1943). C. Ledermanniella aloides (Boupoya et al. 1749). D, E. Ledermanniella bifurcata (D: Boupoya et al. 1954; E: Boupoya et al. 1958). F, G. Ledermanniella pusilla (F: Boupoya et al. 1733; G: Boupoya et al. 1735). H. Ledermanniella pygmaea (H: Boupoya et al. 1764). Photographs: Archange Boupoya.