Gomphonema krammeri E. Reichardt, 2005

Stone, Jeffery R., Kociolek, J. Patrick & Westover, Karlyn S., 2020, Two multi-stigmate Gomphonema species of Africa: Gomphonema kalahariense (nom. nov., stat. nov.) and Gomphonema chemeron (sp. nov.), Phytotaxa 436 (3), pp. 270-282 : 273-274

Gomphonema krammeri E. Reichardt

Although the two forms that Reichardt(2005) identified as Gomphonema krammeri bear a striking similarity to Reichelt’s sketch, when compared directly with Gomphonema specimens collected from the Kalahari region, some differences in the valve outline become apparent. The taxon we observed from ancient lake sediments from the Mababe Basin is distinctly more lanceolate-clavate than G. krammeri but more lanceolate than the more linear-clavate Gomphonema hustedtii , both described in Reichardt (2005). Of the known multi-stigmate Gomphonema , the largest specimens of the taxon we observed from the Kalahari region, when the full range of observed specimens are present, appear most similar in valve outline to G. dubravicense Pantocsek 1892 , originally described from fossil deposits in Europe. However, G. dubravincense can be readily distinguished from the taxon we observed by the presence of multiseriate striae ( Reichardt, 2005), which were never observed in the species we analyzed. Based upon these observations, we believe the species originally described as Gomphonema ventricosum var. africana is not synonymous with G. krammeri , but rather is a distinct species. Thus, we elevate this taxon to species level, recognizing it does not appear to be closely related to G. ventricosum . The epithet “ africanum ” is currently occupied by a species described by West (1907), therefore we have created a new name for this taxon:

Gomphonema kalahariense Jeff.R.Stone & Kociolek , nom. nov., stat. nov. Figures 4–17

Basionym: Gomphonema ventricosum var. africana Reichelt 1903: 779 , Abb. 39, Atti Inst. Bot. Pavis, achter Anhang, 760–784.

Description: Frustules in girdle view wedge-shaped with rows of coarser areolae (typically 4–5) on the mantle separated from the transapical striae by a structureless zone. Valves slightly clavate, relatively narrow, lanceolate ( Figs. 4–11 ), with narrowly-rounded apices. Length 41–76 µm, width 9.7–13.0 µm. Axial area wide, with a unilateral central area due to the presence of a shortened stria (more rarely two striae). Raphe lateral, with external distal ends deflected away from the side bearing the stigmata. Stigmata (2) 3–4 present in the central area, with the number present positively related to valve length. At the border of the central area, striae on the side opposite of the stigmata often end with slightly detached, stigmoid areoles. Transapical striae distinctly punctate, radiate, 7–9 in 10 µm, but at the poles slightly denser (10 in 10µm). Footpole with a bilobed apical pore field. Septa and pseudosepta present at the poles.

In SEM: Striae with roughly 24 (20–26) areolae in 10 µm that are coarsely punctate and consistently uniseriate ( Figs 12–17 ). Stigmata are expressed internally as slits and externally as simple openings. Internally, the proximal raphe ends in both species hook sharply toward the stigmata. Proximal raphe ends lack distinctive central pores. The distal raphe ends terminate internally as small, distinct helictoglossae.

Locality: Mababe, Botswana.

Note: Gomphonema kalahariense has only been observed in tropical and subtropical areas in Africa, from modern and geologically-young lake deposits.

Differential diagnosis: While similar to G. krammeri in size range and striae density, G. kalahariense has a distinctly different outline: it is not lanceolate-rhombic and it does not taper toward the valve ends. It also has a different range of stigmata (2–4), slightly smaller valve length and distinctly narrower in width than G. krammeri . While it has a similar outline to G. dubravicense , it is readily distinguished by being smaller and uniseriate (See Table 1).

Figures

FIGURES 4–11. Light microscope images of Gomphonema kalahariense. Scale bar = 10 µm.

FIGURES 12–17. SEM images of Gomphonema kalahariense. Fig. 12. External valve view. “S” indicates position of stigmata. Fig. 13. Internal valve view. “S” indicates position of stigmta and “PS” indicates evident pseudoseptum. Figs 14, 15. External views. Fig. 14. Headpole. Fig. 15. Footpole. “APF” indicates position of apical pore field. Figs 16, 17. Internal views. Fig. 16. Footpole, showing the pseudoseptum. “H” indicates the helictoglossa. Fig. 17. Headpole, with both pseudoseptum and helictoglossa evident. Scale bars are indicated in the images.