“To effectively manage the invasive introduced subspecies of common reed and avoid misallocating resources,” they write, “land managers require practical, reliable tools to differentiate it from the desirable native subspecies. While genetic tools are extremely useful for identification, morphological identification is a valuable complementary tool that is easier [to use], cheaper, available in the field and thus more accessible for many land managers and researchers.”
In the course of the team’s research, a suite of 22 morphological traits were measured in 21 introduced and 27 native P. australis populations identified by genetic barcoding across southern Ontario. Traits were compared between the subspecies to identify measurements that offered reliable, diagnostic separation. Overall, 21 of the 22 traits differed between the subspecies, with four offering complete separation: the retention of leaf sheaths on dead stems; a categorical assessment of stem colour; the base height of the ligule, excluding the hairy fringe; and a combined measurement of leaf length and lower glume length.
Additionally, round fungal spots on the stem occurred only on the native subspecies and never on the sampled introduced populations.
“The high degree of variation observed in traits within and between the subspecies,” the researchers conclude, “cautions against a ‘common wisdom’ approach to identification or automatic interpretation of intermediate traits as indicative of aberrant populations or hybridization.”
As an alternative, their “five best traits” checklist offers simple and reliable measurements for identifying native and introduced P. australis. It is most applicable, they note, “for samples collected in the late summer and fall in the Great Lakes region, but can also inform best practices for morphological identification in other regions as well.”
The full guide as well as the research that led to it is detailed in the IPSM report. To read it, click here.
The checklist, however, isn’t the only weapon in Dr. McTavish’s arsenal against common reed. This past spring, he publicized details about another initiative involving the release of “two old/new adversaries” of P. australis: a pair of European moth species expected to provide effective biological control of the native-choking plant.
“The two European moths, known by their scientific names Lenisa geminipuncta [pictured below] and Archanara neurica, were selected only after extensive safety testing confirmed they were highly specific to invasive Phragmites, meaning that they can only complete their lifecycle on this plant,” Dr. McTavish said. “The caterpillars of the two moths feed inside the invasive Phragmites stems, causing the weed to wilt or die. In 2019, the Canadian Food Inspection Agency (CFIA) approved the release of both biocontrol agents in Canada. To date, over 17,000 insects have been released at 13 locations across southern Ontario.”
