It is a light green and soft to touch. The stems grow along the ground, and not up. The stems have alternating leaves and seed head also appears like a grass, It is spreading from above the soil, and not from underneath.
Conditions are shady, damp, and probably acidic from crushed pine bark and growing in bare soil. I have several sedges growing in different areas of the garden, but none like this
Thank you for your question, and very helpful photo.
Your description of the leaves as being soft, and clearly a light green, make me inclined to think this is a sod grass plant. It does not appear to have the robust leaves, or the signature mauve/purple shades of the stems of either a crab grass, or a quack grass, nor the height of a sedge plant. As most perennial sod grasses grow larger, and are not trimmed, or mown, they can produce two types of horizontally spreading tillers: rhizomes and stolons. Shallow rhizomes grow horizontally under the soil surface, then the stolons also venture laterally, but above ground, as you mentioned.
One last note: to the left of your planted area, it appears as though you may have some turf lawn, which makes me wonder if your mystery plant may be a rogue sod plant that has employed its adventitious root system to expand its territory into your garden.
It seems that you are primarily interested in identifying this plant, and happy to allow this grass to continue growing, and if that’s the case, I hope this helps.