The genus Scirpus of Renfrew County:
A comparative study

Scirpus hattorianus Makino, Mosquito bulrush

Scirpus hattorianus is common in Renfrew County. It often appears weedy on disturbed woodland trails and often seen with bulblets growing from the axils late in the season (Figure 4). Until recently, many flora treated Scirpus hattorianus as a variety of Scirpus atrovirens and all Renfrew County herbarium records at CAN and DAO have been filed under S. atrovirens requiring examination and verification since many are expected to be S. hattorianus. Those records in CAN have recently been updated and reclassified while those in DAO still require assessment before they can be mapped. The visual characteristics of S. hattorianus and S. atrovirens are indistinct and lead to many incorrect determinations. However, microscopic views of the scales, perianth bristles and achenes will reliably separate these two species (Figure 5). The most obvious difference is the more robust perianth bristles equaling the achene in length for S. atrovirens while, the perianth bristles are more delicate and generally shorter than the achene for S. hattorianus. Although not noted in other floras, I find (at least for the Renfrew County specimens) that the scales are distinctive: S. atrovirens has spikes along the distal margin of the scale while S. hattorianus only has spikes on the mucro of the scale (looking like the colloquial "thagomizer" on the tail of Stegasaurid Dinosaurs). Unfortunately, a field lens can hardly discriminate these features (Figure 1 at full resolution is equivalent to a 10x loupe and the naked eye) so bringing a few spikelets from mature specimens home to the microscope is usually necesssary to confidently identify.

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