Propagating Nitella flexilis: Splitting the Smooth Stonewort

How to propagate Nitella flexilis, a soft, fine-branched charophyte alga, by gentle fragmentation and oospores — a delicate stonewort anchored by rhizoids, not roots.

Overview

Nitella flexilis, the smooth or slender stonewort, is a freshwater charophyte green alga that occurs on every continent except Australia. It is robust in length, growing up to about a metre on slender axes around 1 mm wide, with branchlets in whorls divided once or twice, giving the fine, translucent, forked look that distinguishes it from the calcified Chara. It is an alga, not a vascular plant, and is anchored by rhizoids rather than true roots.

Propagation Method

Propagation is primarily vegetative through fragmentation: a separated portion of the thallus re-anchors with rhizoids and grows on. As a charophyte it also reproduces sexually via oospores, the resting zygotes typical of the Charales, which can establish new growth. Its large cells and ease of cultivation, which made it a laboratory model organism, also make fragments quick to take hold in the aquarium.

Fragmentation / division — separate a healthy tuft gently and let it re-anchor with rhizoids.
Oospores — sexual resting spores that can germinate into new thalli.

Step-by-Step

Pick a healthy tuft with bright, intact, finely forked whorls.
Tease off a portion by hand; the soft tissue tears easily, so work slowly and gently.
Set the fragment in contact with the substrate so new rhizoids can anchor it.
Keep it under medium light in clean, soft to moderately hard water to encourage growth.
Leave it undisturbed until rhizoids hold and fresh feathery whorls extend.
For sexual increase, let a mature stand fruit so oospores can seed new growth.

Conditions for Healthy Growth

Provide cool to moderate temperatures around 12–24 °C, pH about 6.0–8.0 and GH 4–18, under medium light. Unlike Chara it does not depend on heavy calcification, so it tolerates soft to moderately hard water, which suits coldwater and shrimp tanks. No added CO2 is required.

Maintenance

Keep the water clean and lighting steady, and thin the tufts when they grow dense. Because the strands are delicate, remove any torn or decaying pieces promptly so they do not break down and cloud the water. Handle the alga as little as possible to avoid shredding the fine whorls.

Common Challenges

Fragile whorls shredding under rough handling or strong flow.
Decaying fragments fouling the water if torn pieces are left in place.
Smothering by debris or faster plants on its fine, soft strands.
Confusing it with calcified Chara and pushing hard alkaline water it does not need.