Ledermanniella pusilla (Warm.) 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 pusilla (Warm.) C.Cusset (Cusset 1974: 273)

Figs 6F, G , 7A

Sphaerothylax pusilla Warm. ( Warming 1899: 146, pl. 39)

Dicraeanthus pusillus (Warm.) C.H.Wright ( Baker and Wright 1909: 127)

Inversodicraea pusilla (Warm.) Engl. ( Engler 1926: 461)

Type.

CAMEROON • Bipindi, in the Lokundje rapids [" Bipinde, an den Lokundje-Schnellen "]; 10 Aug. 1896; [3°05 ’00” N, 10°25 ’00” E]; 70 m; fl., fr.; Zenker 1050; holotype: B; isotypes: BM [BM000910383], G [G00014258, G00014259], K [K000959889], L [L0035207, L0035208], M [M0108129], U [U0005651], W [W18980001777], WAG [WAG0002675] .

Distribution.

Cameroon, Gabon, Democratic Republic of the Congo. Before 2017, this species was known from nine collections throughout its range, including two from Gabon, in the Ogooué river at Booué and the Ogoulou river at Mitingo. The authors and colleagues have collected this species 119 times since 2017, which makes it the most commonly collected Podostemaceae species of Gabon. In Gabon, L. pusilla is found in all the rivers explored by authors and colleagues in the Monts de Cristal area, as well as the Ogooué, Ngounié, and Louetsi rivers, and the Offooué and Ivindo rivers, near their confluence with the Ogooué. This species is expected to be present in Equatorial Guinea as well as in the Republic of the Congo.

Habitat and ecology.

In Gabon, rapids in rivers from ca 10 to 650 m wide, 35-590 m in elevation. It is usually abundant where encountered, forming dense and large mats. Flowers and fruits were collected in July, August, and September, as well as in January, February, and November outside of Gabon. In the Ogooué river, it seems to share micro-habitats with Inversodicraea annithomae , I. thollonii , Ledermanniella aloides , Macropodiella hallaei , and Tristicha trifaria . It is also often the only species found in rapid areas of small forested rivers in the Monts de Cristal area. In Gabon, this species is very ecologically tolerant, being found in slow or fast-flowing water.

Notes.

The Gabonese material corresponds to the specific concept of Cusset, who already noticed the ability of this species to produce stemless fertile shoots as well as developed stems. The recent collections mostly comprise stemless individuals, but some collections (Boupoya 1751, 1935, and 1936) show elongated stems up to 4 cm long. The root morphology appears also quite variable, with most collections displaying ribbon-like roots up to 3 mm wide, but sometimes also crustose root, up to 8 mm in diameter (Boupoya 1467, for instance). All leaves are linear, varying in length (up to 2.5 cm long in Boupoya 1935), with a good proportion of them being dichotomously divided at least once, the proportion varying depending on the collection. Exceptionally, all leaves can be entire, which brings the question of the validity of L. linearifolia . This species, endemic to southern Cameroon, always shows entire thread-like leaves up to 2 cm and may represent a local form of the more widespread L. pusilla . In addition, both L. linearifolia and L. pusilla belong to the same subclade within the Ledermanniella -Dyad group (see molecular data and illustrations in Moline et al. 2007: fig. 6A-G; Thiv et al. 2009; Koi et al. 2012). While in L. pusilla , most leaves bear stipules, some are also lacking such features, sometimes on single shoots. Exceptionally, some double-sheathed leaves (between two spathellae on a single stemless fertile shoot) can show up to four stipules (Boupoya 1731). Double-sheathed leaves are a peculiarity of many podostemoid members in America and Africa, always positioned at the fork of dichotomously branching stems (see Cook and Rutishauser 2007: 306; Moline et al. 2007: 163). One collection showed a couple of flowers having only one stamen (Boupoya 1725), and a couple of flowers amongst the several hundred observed showed three stigmas instead of two. Despite important morphological variability, L. pusilla can be recognized by the combination of pollen as dyads, leaves distichously arranged, linear, and almost never strictly entire, flowers with (usually) stalked spathellae, almost always bearing two stamens, among other minor characters.

Figures

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.

Figure 7. Distribution maps of Podostemaceae in Gabon. A. Ledermanniella pusilla (red diamonds), L. tenuifolia (grey circle). B. Ledermanniella pygmaea (grey circles), Macropodiella heteromorpha (red diamonds). C. Macropodiella hallaei (grey circles), Saxicolella nana (red diamonds). D. Tristicha trifaria (grey circles).