Q.2 Which algae shows fungus-like branched, coenocytic and siphonaceous thallus?
- Navicula
- Vaucheria
- Volvox
- Polysiphonia
Vaucheria is the alga that exhibits a fungus-like branched, coenocytic, and siphonaceous thallus, resembling fungal hyphae in its aseptate, multinucleate structure.
Question Breakdown
This question assesses thallus organization in algae, a key botanical classification criterion. “Fungus-like” refers to the non-septate (aseptate), tubular growth; “branched” indicates irregular branching; “coenocytic” means multinucleate without cross-walls; and “siphonaceous” describes the tube-like, vacuolate body typical of Siphonales.
Option Analysis
Navicula
Navicula, a diatom (Bacillariophyceae), has a unicellular, silicified frustule (two-valved shell), not branched or coenocytic. It’s planktonic with golden-brown plastids.
Vaucheria
Vaucheria (Xanthophyceae, yellow-green algae) forms a branched, coenocytic siphonaceous thallus – a single, aseptate filament with peripheral cytoplasm, central vacuole, and nuclei. Anchored by rhizoids, it mimics fungal hyphae and inhabits moist soils or freshwater.
Volvox
Volvox (Chlorophyceae) is a hollow spherical colony of biflagellate cells embedded in gelatinous matrix, not branched or coenocytic individually.
Polysiphonia
Polysiphonia (Rhodophyta, red algae) has a multiaxial, septate filamentous thallus with branched axes, but cells are partitioned by septa, lacking coenocytic nature.
Correct Answer: Vaucheria – Precisely matches all descriptors as a classic siphonaceous example.
The fungus-like branched coenocytic siphonaceous thallus defines Vaucheria algae, a yellow-green alga with a tubular, aseptate body mimicking fungal growth. This structure supports its saprophytic or aquatic habitats, making it essential for algal classification in competitive biology exams.
Thallus Types in Algae
Algal thalli vary from unicellular to complex, with siphonaceous forms unique for lacking septa:
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Coenocytic siphonaceous: Vaucheria – Branched tubes, multinucleate, fungus-like.
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Unicellular: Navicula – Diatom frustules.
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Colonial spherical: Volvox – Flagellated cells in sphere.
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Septate filamentous: Polysiphonia – Multiaxial reds.
Vaucheria’s thallus enables rapid apical growth without cell division, housing discoid chloroplasts for photosynthesis.
Vaucheria’s Distinct Features
Its branched filaments (up to cm long) bear oogonia/anthridia for sexual reproduction, with rhizoids for attachment. Unlike septate algae, coenocytic nature allows cytoplasmic streaming, relevant to your microbiology studies.
Alga Thallus Type Key Traits Navicula Unicellular diatom Silicified valves Vaucheria Branched coenocytic siphonaceous Aseptate, fungus-like Volvox Spherical colony Gelatinous, biflagellate Polysiphonia Septate multiaxial Branched but cellular -
