Old Genus Revived For Potamogeton PectinatusThe cosmopolitan Fennel-leaved pondweed (Potamogeton pectinatus L.), is an uncommon waterweed in New Zealand wetlands. In 1912 the German botanist Börner placed it and other allied species into a segregate genus Stuckenia Börner, as S. pectinata (L.) Börner. However, Börner’s genus was overlooked until 1997, when it was reinstated by Czechoslovakian botanist Josef Holub. Although Stuckenia seems to have been widely adopted worldwide, the genus has not been used in New Zealand before, so NZPCN provide a summary of its defining characters.
As currently circumscribed the Potamogetonaceae comprises three genera, Potamogeton L., monotypic Groenlandica J.Gray, and Stuckenia Börner. Börner erected Stuckenia to accommodate those species of Potamogeton with long stipular sheaths, tubular leaves with air channels bordering the midrib, flexuous peduncles, hydrophilous pollination and a hexaploid chromosome number (x = 13, 2n = 78 (6x)). In Stuckenia the stipules are fused (adnate) to the basal part of the leaf and form a sheath with a distinct ligule, they are adnate for at least 2/3 of their length. Similar sheaths though present in Potamogeton s.s are scarce, only two species P. robbinsii Oakes and P. serrulatus Regel et Maack are known to consistently possess this character, and even then the stipules are adnate for only ½ their length. The emergent and submerged leaves of Stuckenia are always sessile, while in Potamogeton they are petiolate. A further difference is that the submerged leaves of Stuckenia differ consistently from those of Potamogeton and Groenlandica, in that they are characteristically grooved and channelled, turgid and opaque. In these latter genera they are without grooves or channels, usually translucent and flat. The emergent peduncles of Stuckenia are long, slender, flaccid, wiry (flexuose), while the inflorescences are usually interrupted; those of Potamogeton are normally compact. Aside from the hydrophilous pollination mechanism (anemophilous in Potamogeton), the pollen grain morphology of Stuckenia is also very distinct from both Potamogeton and Groenlandica. Chromosome counts for Stuckenia are 2n = 78, except in S. pectinata where an aneuploid series has been reported, though in New Zealand this species, based on one recent unpubl. count (P. J. de Lange pers. comm.) has 2n = 78. In Potamogeton the usual chromosome number is 2n = 26 x = 13, (2x) or 2n = 52 (4x), though again New Zealand samples of P. cheesemanii have been reported with 2n = 28. Aside from these differences further support for Stuckenia can be seen in the pattern of hybridisation within the family; there are no intergeneric hybrids known between Potamogeton and Stuckenia. Stuckenia based on molecular and cladistic data is a sound monophyletic group distinct from Potamogeton and Groenlandica.
In New Zealand we have the one indigenous species, S. pectinata which, aside from its filiform leaves and interrupted inflorescences is also distinguished from the other New Zealand Potamogeton by its tuberous condition. S. pectinata while uncommon throughout much of New Zealand, can at times be abundant and almost troublesome as an aquatic weed. Recent field surveys by NIWA suggest that its current threat assessment of “Chronically Threatened/Gradual Decline” is unwarranted and that it fits “At Risk/Sparse” better (P.D. Champion pers. comm.).
NZPCN thank Peter de Lange for the provision of his unpublished New Zealand count for Stuckenia pectinata and Paul Champion for comments on the conservation status of the species.
Les, D.H.; Haynes, R. 1996: Coleogeton (Potamogetonaceae), a new genus of pondweeds. Novon 6: 389-391
Holub, J. 1997: Stuckenia Börner 1912 – the correct name for Coleogeton (Potamogetonaceae). Presilia 69: 361-366.