Question

Coralloid roots are associated with

• A. Pinus
• B. Cycas
• C. Gingko
• D. Equisetum

Hint:

Coralloid roots are a distinguishing feature of Cycas (a cycad), primarily due to their unique morphology and symbiotic relationship with nitrogen-fixing cyanobacteria.

Answer 1

The Correct Option is B

Step 1: Define coralloid roots.
Coralloid roots are specialized roots found in certain plants. They are unique in their morphology, typically growing negatively geotropically (upwards, away from gravity), branching dichotomously, and having an irregular, branched, coral-like appearance. Their most significant feature is their symbiotic association with nitrogen-fixing cyanobacteria (blue-green algae), such as \textit{Nostoc} or \textit{Anabaena}, which reside in a specific zone within the root cortex. This symbiosis provides the host plant with fixed nitrogen. Step 2: Evaluate each option for the presence of coralloid roots.
(A) Pinus: \textit{Pinus} (pine trees) belongs to the conifers, a group of gymnosperms. Pines are well-known for forming mycorrhizal associations (symbiotic relationships with fungi) in their roots, which aid in nutrient absorption. However, they do not possess coralloid roots.
(B) Cycas: \textit{Cycas} is a genus belonging to the cycads, an ancient group of gymnosperms. Cycads are famously characterized by the presence of coralloid roots. These roots develop near the soil surface and contain nitrogen-fixing cyanobacteria, providing the plant with a source of usable nitrogen.
(C) Ginkgo: \textit{Ginkgo biloba} is another unique gymnosperm, often referred to as a "living fossil." It has a distinct fan-shaped leaf morphology. While it has a well-developed root system, it does not form coralloid roots.
(D) Equisetum: \textit{Equisetum} (horsetails) are part of the pteridophytes (fern allies). They have rhizomes and adventitious roots for anchorage and absorption. They do not possess coralloid roots. Step 3: Conclude the association.
Based on botanical knowledge, coralloid roots, with their symbiotic association with nitrogen-fixing cyanobacteria, are a characteristic feature of Cycas.