Bryothamnion

Bryothamnion · also called Red Razor, Alsidium, Alsidium triquetrum

Bryothamnion is a firm, branching red macroalgae. B. triquetrum, called Red Razor, carries saw-toothed edges along stiff stems. A 2018 study merged the genus into Alsidium, so newer papers use the name Alsidium triquetrum. It is seldom kept, and keepers have little experience with its care.

Educational only. Some KinStation entries are reviewed by licensed veterinarians, but none can replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.

Quick facts

Category	Marine & Algae
Family	Rhodomelaceae
Native origin	Tropical and subtropical American coasts, including the Caribbean and Brazil
Care difficulty	Intermediate
Light	Medium light
Pet toxicity	Toxicity unknown

Light

Hobby notes suggest it is not fussy, growing under moderate reef lighting and also under brighter light, with color shifting as intensity changes. Keepers have little firm data for Red Razor itself, so start at a moderate level and adjust slowly while watching the color.

Water

Standard reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. No specific needs are recorded. Keep salinity and temperature stable, and leave nitrate and phosphate at measurable levels. Wild plants live in shallow subtidal water on semitropical to tropical shores, so warm, steady reef conditions are a fair match.

Soil & potting

Grows attached to hard surfaces, not rooted in sand. Hobby notes describe fixing pieces to rock or shell with a small dab of super glue, which suits its firm stems. Let the base touch the rock, and keep the branches clear so water can move freely through them.

Environment — humidity, temperature, placement

A shallow subtidal alga from warm American coasts and the Caribbean. Moderate to good flow in a display suits its rigid form, and dead spots should be avoided. Standard reef temperature, 23-27 C (74-80 F), is appropriate. Keepers have little data on it in refugiums.

Propagation

Growth is reported as moderate to slow. Trim a branch and glue or tie it to new rock to start a new plant. Keepers have little firm data on Red Razor, but field cultivation of Alsidium triquetrum has been described, which suggests pieces can regrow when conditions suit them.

Toxicity detail

No toxicity data for tank animals was found, so the rating stays unknown. Lab studies of its extracts looked at rodents and are no guide to aquarium safety. No grazing deterrent or coral smothering risk is recorded. As with any rarely kept macroalga, watch corals it touches.

Varieties & cultivars

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

Natural forms1

Red Razor

Alsidium triquetrum (formerly Bryothamnion triquetrum). A branching red alga with serrated edges along its stems. The saw-toothed outline gives it the name Red Razor.

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