Near a stream.
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This plant isn't growing far from my house - what features should I look for to confirm the ID?
... Per Stace in C. oppositifolium the leaves are opposite (in pairs), up to 2 cm in size, cuneate (wedge-shaped) to rounded at their base (junction with stalk) with the petiole (stalk) about as long as the blade; in C. alternifolium they are alternate (one per node), up to 3 cm (or more) in size, cordate (heart-shaped) at their base, and with the petiole much long than the blade. (The last point suggests that I was wrong, and that it's C. oppositifolium.)
Lat/Lng: 54.2889, -0.4146
OS grid ref: TA032893