Inversodicraea tenax (C.H.Wright) Engl. ex R.E.Fr. (Fries and Rosen 1914: 56)

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 tenax (C.H.Wright) Engl. ex R.E.Fr. (Fries and Rosen 1914: 56)

Figs 3H, I , 4B

Dicraea tenax C.H.Wright ( Baker and Wright 1909: 125) - Type: same as for Inversodicraea tenax .

Ledermanniella tenax (C.H.Wright) C.Cusset ( Cusset 1974: 275) - Type: same as for Inversodicraea tenax .

Inversodicraea tanzaniensis Cheek, syn. nov. ( Cheek et al. 2020: 31) - Type: TANZANIA • Distr. Iringa c. 1700 m Ruhudji river ["Stromgebiet des oberen Ruhudje, Landschaft Lupembe, nördlich des Flusses"]; 22 Aug. 1931; [9°18 ’31” S, 35°11 ’20” E]; 1700 m; fl., fr.; Schlieben 1131A; holotype: K; isotypes: B†, BM, BR [BR0000017827522], EA, G, LISC, P [P00179369], PRE, Z, ZT.

Type.

ZAMBIA • Victoria Falls , Livingstone Island; [17°55 ’26” S, 25°51 ’14” E]; 885 m; fl., fr.; 17 Sep. 1906; Kolbe 3149; holotype: K [K000435188]; isotypes: BM [BM000797689], BOL [BOL135706] .

Distribution.

Gabon, Democratic Republic of the Congo, Angola, Namibia, Tanzania, Botswana, Zambia, Zimbabwe. Though recent collections revealed the presence of this species in Gabon, it has in fact been collected in the country as early as in 1926 (Le Testu 5983), but it was misidentified as I. ledermannii by Cusset (see Notes under that species). In addition, examination of the collection N. Hallé 4451 collected on the Kinguélé waterfall on the Mbé river (Monts de Cristal) in 1968, and identified as I. cristata by Cusset, revealed the presence of one fertile individual identified by us as I. tenax , now as the collection number N. Hallé 4451B, separated from N. Hallé 4451A, which represents I. cristata . Material associated with I. ledermannii from the Democratic Republic of the Congo and Angola was not examined for this study, but should be checked for their pollen. If monads are observed (i.e. not dyads as typical for I. ledermannii ), this material would be best associated to I. tenax , which could link this species’ original distribution with the newly discovered Gabonese subpopulations.

Habitat and ecology.

In Gabon, rapids and falls in rivers from ca 10 to 40 m wide, 50-510 m in elevation (up to 1,700 m in Tanzania). It appears to be quite rare at the few sites where it has been encountered. In Gabon, flowers and fruits were collected in January, June, July, and August. It grows intermingled with I. cristata (N. Hallé 4451A and 4451B) and close to L. pusilla in the Monts de Cristal area. Collections made from small rivers in Monts de Cristal (north-western part of Gabon), as well as larger rivers (Komo, Abanga, Offooué) revealed important ecological tolerance, previously unsuspected for this species.

Notes.

The discovery of I. tenax in Gabon is surprising, but the pollen as monads shown by the Gabonese material and the close examination of material from southern Africa leaves no doubt about the identity of the Gabonese collections. The recently collected Gabonese material revealed important morphological variability: stem-scales appear to have a variable number of dorsal projections (from 0 to 2, often on the same individuals) and of lobes (3 to 5), whereas Cusset’s description of the species ( Cusset 1983) mentioned 3-dentate stem-scales (or with 3 lobes), and most often with 2 dorsal appendages. The Gabonese material also shows a great variety in the proportion of dorsally appendaged stem-scales versus dorsally smooth stem-scales, with some individuals nearly or completely devoid of dorsal appendages. Nevertheless, the pollen as monads consistently observed on this material allows to rule out I. ledermannii (that has pollen as dyads). The examination of the Paris isotype of the recently described I. tanzaniensis (Schlieben 1131A) showed a similar pattern of stem-scales variation, bearing 3 to 5 lobes and from 0 to 2 dorsal appendages, despite the original description ( Cheek et al. 2020) mentioning the clear absence of dorsal appendages as a strong difference with I. tenax . Stem-scale variation appears more important at the tip of shoots, on stem-scales subtending spathellae, in both the Gabonese collections as well as I. tenax material and the isotype of I. tanzaniensis . Stem-scale morphological variability within the genus Inversodicraea (including in I. tenax ) was already described by Cusset (1983), who mentioned differences in shape and size of stem-scales depending on their position in the stem. Considering the clear continuum between the presence and absence of dorsal appendages, we consider that their absence cannot be used to discriminate material from an otherwise similar species. In addition, all dried capsules observed on the isotype of I. tanzaniensis as well as the Gabonese material showed 8-ribbed capsules, including two commissural ribs clearly visible, whereas Cheek et al. (2020) mentioned I. tanzaniensis as having 6 ribs instead of 8 being a strong difference with I. tenax . Among other differences between I. tenax and I. tanzaniensis are the lengths of the tepals and gynophore. The Gabonese collections showed tepals of ca 0.8 mm of length, similar to what was described for I. tanzaniensis , but slightly longer than mentioned on the original description of I. tenax (0.5 mm), and a gynophore of ca 0.5 mm, similar to what was described for I. tenax , but slightly longer than mentioned for I. tanzaniensis . We believe those differences are not relevant, especially since some variability has also been observed by the authors on other species. Finally, another important character mentioned by Cheek et al. (2020) to discriminate I. tanzaniensis from I. tenax is the length of stem, of up to 20 cm for I. tenax whereas I. tanzaniensis has 5-8 cm long stems. The recently collected Gabonese material showed both stemless individuals (Boupoya et al. 2418, 2420, 2422, 2423), or with stems of up to 3 cm long (Boupoya 1709, 2429, 2430, 2432). We suggest a cautious approach when considering the length of stem as a character to discriminate species. If some Podostemaceae species clearly never show elongated stems, especially in Ledermanniella ( L. thalloidea (Engl.) C.Cusset and L. aloides , for instance), the prolific material collected by authors and colleagues suggests a strong intraspecific variability in that matter, that was only sporadically mentioned by Cusset (1983) in Ledermanniella ( L. pusilla and L. bifurcata ), and that was largely unsuspected for Inversodicraea until now. Recent material collected in Gabon shows that I. annithomae , I. thollonii , and I. tenax (among others) can show stemless shoots as well as developed stems, sometimes on single individuals. In addition, such variability is not surprising considering species that are widespread and known from a variety of micro-habitats, such as I. tenax . When developed stems are observed for a given species, stem length might therefore better reflect ecological preferences. Our observations also suggest that developed stems are often associated with strong currents. For all the above-mentioned reasons, we believe it is best to consider I. tenax as a widespread, morphologically variable (with continuums) and ecologically ubiquitous species, which comprises I. tanzaniensis .

Figures

Figure 3. Photographs illustrating a selection of species treated in this paper. A, B. Inversodicraea annithomae (A: Boupoya et al. 2444; B: Boupoya et al. 2689). C. Inversodicraea boumiensis (Boupoya et al. 1748). D, E. Inversodicraea nicolasii (D: Texier et al. 2247; E: Texier et al. 2334). F, G. Inversodicraea paulsitae (Boupoya et al. 1750). H, I. Inversodicraea tenax (H: Boupoya et al. 2432; I: Boupoya et al. 2430). Photographs: Igor Nguimbit (A), Archange Boupoya (B, C, F-I), Nicolas Texier (D, E).

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).