Gelidium

Gelidium · also called Purple Palms

Gelidium is a genus of wiry red macroalgae, best known as a source of agar. The kept form, Purple Palms, is reddish purple and changes shape with its surroundings, branching in some tanks and forming thick, stranded clumps in others. Some wiry relatives are nuisance turf in reef tanks.

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Quick facts

Category	Marine & Algae
Family	Gelidiaceae
Native origin	Seas worldwide; wiry turf species are circumtropical
Care difficulty	Intermediate
Light	Bright indirect
Pet toxicity	Toxicity unknown

Light

A reference entry for G. pusillum says it likes bright light, and the kept form shifts its growth with lighting and flow. Give it good reef light and expect it to look different from tank to tank. Hold intensity steady once you like its form, since changes can reshape new growth.

Water

Standard reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. The related G. pusillum thrives in nutrient-rich water, so higher nitrate and phosphate may push growth along. Keep nutrients measurable, and prune if it starts to spread. No other needs are recorded.

Soil & potting

Grows on hard surfaces, and turf species form mats on rock in the intertidal, so it does not belong in sand. Tie a piece to rock or rubble with line. Watch where it settles, because a wiry turf that gets a foothold on display rock can be hard to clear away again.

Environment — humidity, temperature, placement

Related species like very good water movement, so give it moderate to strong flow in a display or macroalgae tank at standard reef temperature, 23-27 C (74-80 F). Flow and lighting decide whether it grows as branches or clumps, so its position matters more than usual.

Propagation

Keepers have little record of propagating the kept form. Trim a section and tie it to fresh rubble. Keep an eye on spread: a reference entry calls G. pusillum a nuisance that can crowd out desired growth and is hard to eradicate, so do not assume the kept form will stay put.

Toxicity detail

No toxicity data for tank animals was found, so the rating stays unknown. The recorded risk is spread: G. pusillum is listed as unsuitable for reef tanks because it can crowd out other growth. No grazing deterrent is recorded. Agar is a food product, which says nothing about tank safety.

Varieties & cultivars

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

Natural forms1

Purple Palms

Gelidium sp. A reddish-purple alga that can branch like Haliptilon or mass into thick, stranded clumps like Chondria. Flow, lighting and other tank conditions decide which form it takes.

Flow and lighting shape its form, so expect it to look different from tank to tank.