Ludwigia repens. This plant is one of the easiest red plants to grow, displaying small oval-teardrop shaped leaves with pink to dusky red colouration. It grows rapidly, and with regular trimming and replanting side shoots are easily formed to grow colourful mid-ground bushes.
It is easy to grow, requiring moderate to intense lighting (this will affect vibrancy of colour) and regular micronutrient fertilisation. CO2 is not required, making this plant an excellent choice for both low-tech and high tech aquariums.