Potamogeton sp (cheesemanii or sulcatus)

Pondweed at Majura, ACT

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Identification history

Potamogeton sp (cheesemanii or sulcatus)	18 Jan 2021	michaelb
Potamogeton sp (cheesemanii or sulcatus)	18 Jan 2021	michaelb
Potamogeton sulcatus	17 Jan 2021	michaelb
Unidentified	16 Jan 2021	JaneR

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User's notes

Plants mostly stranded on wet muds by falling water levels: occurring infrequently in this dam, only on southern shore.

13 comments

JaneR wrote:

17 Jan 2021

I assigned it to Potamogeton cheesemanni rather than P. sulcatus due to number of longitudinal veins being two few for P. sulcatus, and number of flowers in spike being too few also. But leaf width length was indeed more like P sulcatus

michaelb wrote:

17 Jan 2021

Do you think this sighting ID is correct for Potamogeton cheesemanni ?:- Potamogeton cheesemanii (Pondweed)
It is different from this one:- Potamogeton cheesemanii (Pondweed)

JaneR wrote:

17 Jan 2021

Hi Michael,

How do you decide what characteristics to rely on ?
I can see that the wider more lime-green leafed plants look different from the narrower, darker plants; but wonder if that is phenological differences: early season v later older plants.

I have just checked a specimen collected from the same dam on 9 Dec 2020. Overlapping characteristics are leaf size (3.7x2.6, 5.8x3.4 - either species); rounded apex; number of flowers is 20, or 21. Characteristics that fit P. cheesemanii are: longitudinal veins are 15, and infructescence is 1.8 cm long.
Sighting 4198017 also looked like it should be P.sulcatus but had metrics that better suited P. cheesemanii.
Sighting 4352668 was earlier in the season; but has only 9-11 longitudinal veins (no specimen collected so have no other info).
I don't know how to resolve this - ??

michaelb wrote:

18 Jan 2021

My botanical skills are limited, so I can't resolve it. We need trained botanist. The problem of differentiating the two species will continue, so I have added a new name to the species list "Potamogeton sp (cheesemanii or sulcatus)". If we can't solve the problem we can classify it that way:- https://canberra.naturemapr.org/species/46052

JaneR wrote:

18 Jan 2021

that is an excellent solution, responsible and practical. if resolution requires detailed examination, then ID down to species will otherwise always be a stumbling block for CNM.

michaelb wrote:

18 Jan 2021

Thanks Jane

JaneR wrote:

18 Jan 2021

Should this be applied retrospectively to other Potamogeton contentious ID ?

michaelb wrote:

18 Jan 2021

I've re-ID Potamogeton sp. & moved a few into the new grouping, only 2 left:- https://canberra.naturemapr.org/species/22322

Tapirlord wrote:

14 Feb 2023

My understanding is that p.sulcatus has broader leaves ovate-elliptic as opposed to p.cheesemanii which will have lanceolate-ovate (never elliptic). p.sulcatus has longer infloresence with crowded flowers (usually greater than 20), while p.cheesemanii has short infloresence (under 3cm) & less crowded infloresence. as jane says p.sulcatus is said to have more than 20 veins per leaf but this can be difficult to determine from photos. i would say considering everything this is most likely p.sulcatus while the sighting you reference michael (Potamogeton cheesemanii (Pondweed)) is certianly p.cheesemanii.

Tapirlord wrote:

14 Feb 2023

Also I seem to be having issue with CNM comments (I can't have capitals & hyperlinks in the same comment).

JaneR wrote:

14 Feb 2023

the counts of veins and flowers on inflorescence were made on actual plant material at the time. These are (for me) stronger characteristics than leaf shape, and so lead me to P cheesemanii: which was a puzzle as leaf shape did look like P. sulcatus.

michaelb wrote:

15 Feb 2023

Hi Ciaran, I agree there is a bug whereby capitals are lost with hyperlinks.

AaronClausen wrote:

15 Feb 2023

Thanks @Tapirlord @michaelb we'll sort this shortly.

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