Caulerpa mexicana consists of erect fronds with flattened branchlets arising from a creeping stolon with rhizoidal branches attaching it to the substrate. Fronds 15-25cm in height, branchlets 2-4mm in width. Color generally grass-green. Midrib of frond is flat with branchlets oppositely arranged along its axis, branchlets slightly overlapping and pointed upwards with a general feather-like appearance. Similar in structure to C. taxifolia which has a compressed midrib and branchlets that become constricted at the base.