Genus Scirpus Linnaeus, Bulrush
There are seven species of Scirpus found in Renfrew County.
The first three of these are erect plants with a branched ascending/spreading terminal inflorescence carrying spikelets in dense sessile clusters. They all have short perianth bristles with retrorse barbs:
A fourth species, Scirpus pendulus, has cylindrical spikelets on long pedicels. The perianth bristles are contorted filaments not exceeding the scales.
The remaining three species are part of the Scirpus cyperinus complex (wool grasses) having perianth bristles much exceeding the achene and giving the spikelets a woolly appearance:
I follow Schuyler and separate these latter three species by scale color, pedicellate behavior and fruiting period. Leaf width also helps to separate S. atrocintus and S. pedicellatus. Fruiting period is the least reliable indicator because these species are frequent on emergent shorelines and high water can greatly delay the emergence of these species. Regardless, there are no definitive morphological or phenological characteristics that definitively separate these three species and field experience is required to consistently assign their identity.
- S. cyperinus: spikelets sessile or clustered (three or more), scales hyaline to brown, fruiting late July to September.
- S. atrocintus: spikelets pedicelled singly or in pairs, scales blackish, fruiting late June though July (usually dehiscent by August 1 in Renfrew County), leaf width < 5 mm.
- S. pedicellatus: spikelets pedicelled usually singly, scales light brown, fruiting late July through August, leaf width > 5 mm.
Specimens fitting these three descriptions can be readily found in Renfrew County and the distinction between the species is apparent in most cases.
References
Alfred E. Schuyler, A Biosystematic Study of the Scirpus cyperinus Complex, Proceedings of the Academy of Natural Sciences of Philadelphia, Vol. 115 (1963), pp. 283-311.