Marine & AlgaeAdvanced🌤️ Bright indirect

Shaving brush plant

Penicillus sp. · also called Shaving brush, Shaving brush algae, Merman's shaving brush, Penicillus, Neptune's shaving brush

🐾 Pet-safe

Generally non-toxic to cats and dogs.

Penicillus is a calcified green macroalgae that grows as a single stalk topped with a brush-like tuft of filaments, exactly like a shaving brush, rooted into sand. It is decorative but, like other Caribbean calcified algae, it needs a mature deep sand bed and stable mineral chemistry.

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Quick facts

Category	Marine & Algae
Family	Udoteaceae
Native origin	Tropical western Atlantic and Caribbean seagrass beds and sandy lagoons
Care difficulty	Advanced
Light	Bright indirect
Pet toxicity	Pet-safe

Light

Moderate-to-strong reef lighting (medium-high aquarium light / good PAR) to support its calcified structure. Display reef or strong refugium LEDs are suitable; poor light leads to decline. Mapped to bright lighting needs.

Water

Reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. As a calcifier it draws calcium (~400-450 ppm), alkalinity (8-11 dKH), and magnesium (~1300 ppm) - keep these stable and replenished. Prefers mature, low-to-moderate-nutrient systems. No CO2 (marine).

Soil & potting

Roots into the substrate with a buried bulb/rhizoid holdfast, so it REQUIRES a deep, established live sand bed to anchor and feed; it cannot simply be wedged on rock. Plant the stalk base into the sand. No aquasoil or root tabs - it relies on the live sand bed.

Environment — humidity, temperature, placement

Submersed only. No CO2 (marine). Gentle-to-moderate flow; strong current can damage the delicate brush. Best in a display or refugium with an established deep sand bed, placed on the sand in the foreground/midground. A sensitive species better suited to experienced reefkeepers.

Propagation

Spreads by sending up new stalks from its rooted base and rhizoids through the sand bed; not easily fragmented by cutting because of its single calcified stalk-and-brush form. Usually left to multiply naturally in the sand bed.

Toxicity detail

Reef-safe and non-toxic; its calcified, somewhat unpalatable tissue means most herbivores ignore it, so it survives in tangs/herbivore tanks. Not invasive or regulated in the hobby. Remove any bleached/dying brushes to avoid nutrient release.

Growth stages

How this plant changes through its life — each stage often has its own care, diet and space needs.

Photo coming soon

Spore / recruit

Aquatic plants and macroalgae establish from spores, seeds, or drifting fragments that settle and attach to substrate or rock. Many freshwater aquarium plants and marine macroalgae also spread readily from a detached piece that takes root or holdfast.

Photo coming soon

Young growth

Young growth puts out its first blades, fronds, or leaves and anchors with roots or a holdfast. Submersed plants may look different from their emersed form, and growth speeds up as the plant adapts to the water's light and nutrients.

Photo coming soon

Mature

A mature aquatic plant or macroalga reaches its full size and characteristic shape, forming the dense growth, runners, or fronds typical of the species. Established plants spread to fill space and can be divided or trimmed to propagate.

Sources

Penicillus (alga) - Wikipedia (encyclopedia)
Penicillus (Shaving Brush) & Caribbean Calcified Macroalgae - Reef2Reef (care guide)