basically, macro algae lacks a true vascular system (roots, veins, etc.). i know that's way oversimplified, but that's how i look at it. maybe a true "plant weenie" can go further in the explanation.
that being said, the most commonly used macros are from genus
Caulerpa and
Chaetomorpha.
most folks relegate "
Cheato" to their sumps/refugia because it basically looks like a green brillo pad. it grows well, doesn't really "go sexual" like many of the
Caulerpa species, and harbors pods like crazy.
we use several species of
Caulerpa and others in many of our DT's. there are some species/variants of
Caulepra that are labled as noxious weeds, and are illegal in some states in order to keep them out of the ocean where they would impact the local ecosystem due to their quick growth. IMHO, if one is diligent in destroying any prunings (freeze for at least 24 hrs prior to disposal, they present little threat. personally, i freeze everything i don't re-use, noxious or not.
as for recommendations, it's kind of all about preferences. some folks like the look of certain species. i sort of do a "add a few species that i like, where i want them and see what takes hold". i say this because i have some systems where certain macros will grow, but the same macro may not grow in others.
all Caulerpa species are green, altho some of the red macros, such as
Botryocladia sp. are referred to as "Red <insert descriptive name, such as "Grape">
Caulerpa".
the best thing to do is look at lots of pix of macro as well as their requirements and size, and decide what you like.
this is an example of one of our SH tanx. it contains Codium, C. racemosa (green grape), Botryocladia (red grape), i forget the name of the red stringy stuff in the center, but the SH love it for pod hunting, and pink galaxy (a rare calcareous macro). HTH
