Ledermanniella bifurcata (Engl.) C.Cusset (Cusset 1974: 273)

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

Ledermanniella bifurcata (Engl.) C.Cusset (Cusset 1974: 273)

Figs 4C , 6D, E

Inversodicraea bifurcata Engl. ( Engler 1915: 273, plate 178) - Type: same as for Ledermanniella bifurcata .

Inversodicraea minima Engl. ( Engler 1915: 273, plate 176) - Type: CAMEROON • Rapids of the Kienké river, ca 50 km east of Grand Batanga ["in den Schnellen des Kienke oder Kribi-Baches, c. 50 km östlich Groß-Batanga”]; Jun. 1911; [2°48 ’00” N, 10°21 ’00” E]; 90 m; fl., fr.; Mildbraed 5952; lectotype (designated here): U [U 0005647]; isolectotypes: B, BM [BM000910384].

Inversodicraea zenkeri Engl. ( Engler 1915: 273, plate 179) - Type: CAMEROON • Bipindi; Nov. 1908; fl., fr.; Zenker 3811; lectotype (designated here): BM [BM000910385]; isolectotypes: B, WU [WU 0037875].

Type.

CAMEROON • Rapids of the Kienke river , ca 50 km east of Grand Batanga [" in den Schnellen des Kienke oder Kribi-Baches, c. 50 km östlich Groß-Batanga”]; Jun. 1911; [2°48 ’00” N, 10°21 ’00” E]; 90 m; fl., fr.; Mildbraed 5951; holotype: B, isotype: BM [BM000910386] .

Distribution.

Cameroon, Gabon, Republic of the Congo. Kuetegue et al. (2019) as well as Ghogue (2010) mention that this species is present in Equatorial Guinea, but they did not cite collections. We have not been able to find any collection clearly from Equatorial Guinea, aside from Letouzey 15334 from the Ntem river at the border with Cameroon. The presence of this species in this country is nonetheless most probable since it was collected on the Ntem river, and in Gabon. In Gabon, this species is known from one collection (Bogner 761) made at the Kinguélé falls in the Monts de Cristal, but recent inventories at this site revealed it has since disappeared due to the construction of two hydroelectric dams on the Mbé river. We have not been able to retrieve this collection and confirm the identification made by Cusset, although she mentioned it as being deposited in Paris. This species has not yet been found again elsewhere in the Monts de Cristal area, despite recent efforts since 2017. In Gabon, L. bifurcata is also present on the Ogooué river around Lastoursville, as attested by a collection made by Le Testu (7424) in 1929, and nine recent collections made in 2019.

Habitat and ecology.

In Gabon, rapids in rivers from ca 50 to 450 m wide, 150-350 m in elevation (up to 600 m in Cameroon). It appears to be quite rare where encountered. Flowers and fruits were collected in January, February, May, June, July, November, and December. Recent Gabonese fertile collections were only made in July. In Gabon, it has been found once near Saxicolella nana , in the Ogooué. At the Kinguélé falls, past collections made by Nicolas Hallé comprised L. letestui , I. cristata , and I. tenax , along with L. bifurcata , but no information on habitat partitioning was collected. In Gabon, this species was mostly found in fast-flowing water.

Notes.

The recently collected Gabonese material confirmed observations already made by Cusset (1984) concerning the morphological variability of this species, especially the presence of stemless shoots as well as elongated stems. Boupoya 1953 to 1957 and Nguimbit 16 all show only stemless shoots, while Nguimbit 15 shows elongated stems up to 2 cm long. The collection Boupoya 1958 displays elongated stems up to 5 cm long, as well as a few stemless, fertile shoots, on the same individuals. The leaves appear to be variable in shape, most dwarf collections showing no or rarely forked leaves. On individuals with clearly developed stems, most leaves are usually 1-2-times forked. Stipules are also variable, from absent to present, more or less rounded at apex, depending on the material studied, and in variable proportions. Ledermanniella bifurcata appears to generally have two stamens, but in the collection Nguimbit 16, ca 5-10% of its flowers have only one stamen. When it has a dwarf habit, this species is morphologically very close to L. pusilla , except this latter species has pollen as dyads, whereas L. bifurcata has pollen as monads. It is also very similar to another dwarf species with pollen as monads: L. aloides . It can still be differentiated from this species by the combination of at least some leaves being dichotomously divided (vs always entire in L. aloides ), and most importantly the conspicuously stalked spathellae, that show a tapered portion at base (stalk) variable in size, up to 7.5 mm long on Boupoya 1957 (vs spathellae never stalked in L. aloides ). The numerous collections of L. aloides now allow for a better understanding of its morphological variability and its boundaries, therefore permitting a better selection of truly discriminative characters. It is nevertheless not yet the case for L. bifurcata that, despite its wide range of distribution in Central Africa, remains a rarely collected and poorly known species. Phylogenetic studies may also help in clarifying its position relative to allied species such as L. aloides .

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.