The correct answer is (2) Scytonema. False branching of the thallus occurs when a trichome breaks due to cell death or decay, often near a heterocyst, and the fragments emerge from the mucilaginous sheath, mimicking branches.

Option Analysis

(1) Rivularia

Rivularia forms hemispherical or spherical colonies of heteropolar, unbranched or facultatively false-branched trichomes with basal heterocysts and tapered hairs. It typically lacks prominent false branching, as new filaments develop parallel via intercalary heterocysts without sheath breakage.

(2) Scytonema

Scytonema shows classic false branching in its filamentous thallus, where trichomes fragment at heterocysts or necridia, and broken ends protrude from the sheath, often in pairs. This is a defining feature in Cyanophyceae exams.

(3) Oedogonium

Oedogonium, a Chlorophyceae alga, has unbranched filamentous thalli that reproduce via fragmentation, zoospores, or akinetes, with no false branching.​

(4) Volvox

Volvox forms spherical colonies of biflagellate cells undergoing inversion during embryogenesis, lacking any filamentous thallus or branching.​

False branching of thallus is a key algae morphology concept in competitive exams like NEET and GATE Life Sciences, distinguishing filamentous Cyanophyceae from others.​

In Scytonema, false branching arises from trichome breakage at intercalary heterocysts or decayed cells (necridia), with fragments slipping out of the mucilaginous sheath to form apparent branches, often paired. This differs from true branching, involving changed cell division planes.

Rivularia shows radial, tapered trichomes in colonies but minimal or facultative false branching via parallel filament separation.

Thallus Comparison Table

This feature aids nitrogen fixation in harsh environments, relevant for plant sciences and microbiology studies.​