Dichotomaria

Dichotomaria · also called Flat-Branched Pink Thicket, Galaxaura marginata

Dichotomaria is a calcified red macroalgae closely related to Galaxaura, with branches that fork repeatedly. D. marginata forms a rounded ball of flat, white-tipped branches in reddish pink. It draws down calcium and alkalinity, and one reference says it rarely stays alive for long in aquariums.

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Quick facts

Category	Marine & Algae
Family	Galaxauraceae
Native origin	Tropical and subtropical seas, including Hawaii and the Indo-Pacific
Care difficulty	Advanced
Light	Medium light
Pet toxicity	Toxicity unknown

Light

Keepers have little experience with its light needs. Its relative Galaxaura is kept under bright light, so moderate to bright reef lighting, raised slowly, is a fair start. The white tips are a normal feature of D. marginata and are not by themselves a sign of bleaching.

Water

Standard reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. Its somewhat calcified structure needs balanced calcium (~400-450 ppm), alkalinity (8-11 dKH) and magnesium (~1300 ppm), and it competes with corals for them. Keep these levels steady.

Soil & potting

Grows attached to hard surfaces in rocky intertidal and subtidal zones, not in sand, and it mostly reaches tanks riding on coral bases. Leave it on its original rock or coral fragment if you can. Otherwise tie a small ball to rubble and keep its base clear of debris.

Environment — humidity, temperature, placement

One reference asks for moderate water movement, which suits a rounded plant that could otherwise trap debris. Place it on rock in a display at standard reef temperature, 23-27 C (74-80 F), and keep it off corals. Keepers have little experience with it, so watch it closely.

Propagation

Keepers have little record of propagating it. Survival in tanks is uncommon, so treat a healthy plant as a specimen and avoid cutting it at first. If it thrives, a small branch could be removed and tied to rubble, but no reliable method has been described.

Toxicity detail

No toxicity data for tank animals was found, so the rating stays unknown. A related species, Galaxaura filamentosa, damaged corals on contact, so do not let this one rest against corals. Calcified tissue tends to be less palatable to fish. One reference lists it as likely reef suitable.

Varieties & cultivars

Natural forms are the wild species; cultivars are selectively-bred colour or variegation forms of the same plant.

Natural forms1

Flat-Branched Pink Thicket

Dichotomaria marginata. A reddish-pink alga that forms a rounded ball of flat branches tipped with white. It is a close relative of Galaxaura.

Little is recorded about its care, so keep conditions stable and change lighting gradually.