Halimeda species (family Penicillus) are a single stem plant whose tissues contain calcium carbonate. They are sometimes referred to as Cactus algae due to their overall shape. They are a mid sized single stem plant ranging from 2-4" tall, and will have a full root section. Can be planted in the main aquarium, as fish typically don't snack on them. They do like a broad spectrum lighting with moderate flow, and the root ball needs to be buried in sand. They are a great addition to any display tank or refugium. As with most macro algaes, these are great at reducing nitrates and phosphates. They will benefit from calcium and iron supplements.