Water-ribbon

A plant of winter-wet swamps, it grows in full or partial sun. The flowers are like tiny dark green balls along a spike, which turn purple-green then yellowish as they mature. Although small, it forms a substantial part of many wetlands. More clumping than spreading, its copious seeding results in many seedlings near the parent plant.

Maintenance

Unlikely to overwhelm nearby plants. To prevent seeding you can cut off the flower stems when they turn yellowish, but this should not be necessary.