Plant Anatomy: Understanding Stele Types

Plant anatomy involves studying the internal structure of plants. One key feature is the stele, which is the central core of the stem and root, containing the vascular tissues (xylem and phloem).

Characteristic Anatomical Features (Stele Types)

Let's look at the definitions of the characteristic anatomical features mentioned:

• Prostele: This is considered the most primitive type of stele. It consists of a solid cylinder of xylem tissue in the center, completely surrounded by a cylinder of phloem tissue. There is no pith in the center of a protostele.
• Siphonostele: This type of stele evolved from the protostele with the appearance of a central pith. The vascular cylinder (xylem and phloem) surrounds the pith. Siphonosteles can be continuous cylinders or interrupted by leaf gaps (gaps where vascular tissue diverges into leaves). A medullated protostele is essentially a siphonostele with a pith.
• Eustele: This stele is found in many seed plants (gymnosperms and dicots) and some pteridophytes like Equisetum. It consists of vascular bundles arranged in a ring around a central pith. The vascular bundles are typically discrete, with interfascicular regions between them. Conjoint vasculature means xylem and phloem are on the same radius within a bundle.

Identifying Stele Types in Plants

Now let's match these features to the given plants based on their known anatomical structures:

• Lycopodium (Clubmosses): The stems of many Lycopodium species exhibit a protostele. This matches feature (i).
• Marsilea rhizome: The rhizome (underground stem) of Marsilea (Water Clover, a fern) is known to have a siphonostele with a distinct central pith. This matches feature (ii).
• Selaginella species (Spikemosses): Selaginella stems typically have a protostele, often modified into a plectostele (a type of protostele where xylem and phloem are arranged in alternating plates). While it's a protostele, it doesn't fit the descriptions for (ii) or (iii).
• Equisetum (Horsetails): The stem of Equisetum exhibits a stele that is often described as a siphonostele or, more specifically, a modified eustele. It has vascular bundles arranged in a ring around a large central pith, with distinct canals (carinal and vallecular) associated with the bundles. This structure closely matches the description of eustele with conjoint vasculature on the edges of the pith area, especially when considering the discrete bundles around the large pith. This matches feature (iii).

Based on the anatomical characteristics:

• Feature (i) Prostele matches Lycopodium (A).
• Feature (ii) Siphonostele matches Marsilea rhizome (B).
• Feature (iii) Eustele matches Equisetum (D).

Therefore, the correct matching is i - A; ii - B; iii - D.