I saw this plant under a Google image search for alternanthera reineckii, but it doesn't look like any that I've seen? Is it a different plant, or just a variety of A.reineckii?
Link to the websiteTo me it looks like A. reineckii 'mini' without enough light. It would help if you provided/read the original website.
Always at least provide the source of a photograph you do not own ( an no images.google.com is not the source). Unless otherwise stated, images are copyrighted and as such you are not allowed to use them without the consent of the copyright owner.